Over my four years at Indiana University, I got to know Samantha via mutual interests in baking and extragalactic astronomy. While we hadn’t studied the exact same research questions, I knew that she had a deep passion for the “Green Peas”. I’d learned of her interest in these strange galaxies when I attended the Department of Astronomy’s honors colloquium during my junior year of college. A fellow Salzarian undergraduate had worked with Samantha to understand their properties. The following academic year, I learned that Samantha had gotten time on the Hubble Space Telescope (HST) to study the Green Peas. Since she was doing science with a famous telescope, I knew that I had to get the low down on her current research.

What is a “Green Pea”?

So, what is a “Green Pea”? I’m sure that the first thing that comes to your mind is the legume that sometimes gets served with meals. However, in astronomy, this term takes on a new meaning that references their nutritious namesake. Green Peas are galaxies that appear as green, compact objects without much structure in their optical images, and despite their compact nature and small appearance in ground-based images, they come in a variety of sizes, including both dwarf galaxies and normal sized galaxies. Scientists first discovered Green Peas in the well-known citizen science project called Galaxy Zoo. They started Galaxy Zoo in 2007 as a way to save professional astronomers research time by enlisting the general public to aid them in the simple task of morphologically (in layman’s terms, by form or structure) classifying hundreds of thousands of galaxies.

While participating in Galaxy Zoo, some citizen scientists discovered these apparent point sources that appeared shockingly green in their images. In astronomy, galaxies exhibiting green colors are incredibly unusual. Objects, such as stars, usually emit light in a range of wavelengths…kind of like viewing the rainbow of colors exiting a prism after shining white light onto it, with blue on the short end of the spectrum and red on the long end. The ultimate color that we see is based on where in the spectrum the peak emission exists.

However, when you have a collection of such objects (like a galaxy), you will find that the overall color of the aggregate object will usually either be red (when longer wavelengths dominate), blue (when shorter wavelengths dominate), or white (when the shorter and longer wavelengths are about equal in their dominance). As such, to find galaxies that strongly emitted green light was a surprise. The citizen scientists immediately made a chat to discuss these strange findings. Eventually, one of the astronomers on the Galaxy Zoo project decided to actually investigate the Green Peas. Subsequent research led to the discovery that strong OIII (astronomer speak for “doubly ionized oxygen”) emission–an indicator of star formation–was the main culprit behind their unusual green color.

Love at First Sight

Samantha herself fell in love with these quirky galaxies during her undergrad tenure at the University of Kansas. One year, for her birthday, Samantha’s family gifted her a subscription to Astronomy magazine. It was here that she first discovered mention of the Green Peas in a small blurb. The small blurb was not enough to quell her curiosity. To her good fortune, the mention of the Green Peas also happened to mention an astronomy professor at the University of Kansas who studied them with the HST. During a colloquial department gathering, she approached the professor to inquire more about the Green Peas. What she learned from the professor heightened her interest in them. The information also inspired her to work with him on similar subjects for the rest of her undergrad career.

When she got to grad school, Samantha still harbored interest in the Green Peas, but she wanted to keep her options open because finding projects that exactly fit your research interests right off the bat in grad school is unlikely. However, in a stroke of amazing luck, Samantha was able to find this. While meeting with professors at Indiana University, she fortuitously discovered that Dr. Salzer had some Green-pea-like galaxies in a data set he had acquired for his KPNO International Spectroscopic Survey (KISS). These Green-Pea-like galaxies were at redshifts of 0.3-0.5, so they were slightly farther away than the original Green Peas (redshifts of 0.2-0.4). These redshifts make these KISS galaxies at least a few billion light years away. Though that’s not a cosmically far distance in the grand scheme of things, life there would see Earth as it was when bacteria was the dominant life form! Mind-blowing, right?

Dr. Salzer desired to compare these Green-Pea-like galaxies to the actual Green Peas, so the opportunity to work with galaxies like the ones that had captured Samantha’s imagination added to her eagerness to start research. Her good rapport with Dr. Salzer was the icing on the cake. They wanted to focus on studying star formation in these Green-Pea-like galaxies, so during Samantha’s first year as a grad student, they applied for Hubble time in order to get optical broadband (astronomer speak for a filter that lets in a relatively large range of wavelengths of light) imaging to better resolve the galaxies from the KISS data set and to make color gradients to potentially find out where the star formation was taking place in these galaxies.

A Telescopic Gold Mine

Acquiring Hubble time is like acquiring gold: not easy. Due to a variety of factors, applying for Hubble time is an extremely competitive process, so they didn’t end up getting Hubble time that year. Fortunately, Dr. Salzer and Samantha realized that Green Pea galaxies were also interesting in the ultraviolet (UV, for short) spectrum. For many years, astronomers have had difficulty in understanding how ionizing radiation (which usually appears in the UV) escapes from galaxies. They knew that in the early universe, much of the existing gas was neutral. The young, hot stars produced ionizing radiation that escaped their host galaxies to ionize what’s called the intergalactic medium. Unfortunately, because these early galaxies are far away, it is hard to get clear observations of them.

Fortunately, the Green Peas are simultaneously nearby and like their early universe counterparts: they have lots of star formation, are metal (in astronomer speak, any element other than hydrogen or helium) poor, and have measurable ionizing radiation leaks. By then, astronomers had confirmed that the KISS Green-Pea-like galaxies were indeed Green Pea galaxies. The KISS Green Peas thus provided a fresh set of Green Peas to study.

After their failure to secure Hubble time for their optical research ideas for the Green Peas, studying the KISS Green Peas in the UV seemed like a great avenue to pursue further research into the Green Peas. Thus, Dr. Salzer and Samantha applied again for Hubble time–but in the UV this time instead of the optical. Much to the happy surprise of both of them, Hubble’s time allocation committees granted them the high distinction of being in the 181 successful proposals out of 1,019 total proposals that year (that’s about a 17.8% acceptance rate!). 

Hubble’s Surprising Talents

Alright, I know what you’re thinking. You’re probably thinking, “Hold up a second, Madeline! Isn’t Hubble an optical telescope?” Well, you would be correct in the assertion. Stunning optical observations are what have made Hubble famous to the general public. However, I share your shock that Hubble does much more than taking many of NASA’s pretty pictures. One of Hubble’s surprisingly many talents is doing UV spectroscopy with the Cosmic Origins Spectrograph (COS) instrument. COS is a UV spectrograph, an astronomical instrument used to measure the properties of light–particularly to determine the chemical makeup of an object. This particular spectrograph provides astronomers with both UV images (used to help Hubble acquire objects for observation) and UV spectra. Astronomers can then see the object as it appears in the UV and examine the chemical makeup of the object. 

Perhaps more shocking than the existence of Hubble’s UV capabilities, it’s the only US-based telescope able to make UV observations. The UV part of the electromagnetic spectrum is actually blocked by our atmosphere. While fortunate for our skin due to UV light’s ability to damage skin, this is unfortunate for UV astronomers. This scientific fact means that if astronomers want UV observations, they must be done from space. Thus, Hubble’s COS instrument fills in a much needed gap in observing capabilities.

However, Hubble is an aging telescope at 30 years young. Due to orbital decay, it is expected to reenter the atmosphere some time in the 2030s or 2040s. Astronomers across the field naturally want to make the most of this world-class telescope before it dies a fiery death. Therefore, Hubble’s unique UV capabilities and impending demise by orbital decay give astronomers with UV projects an edge in acquiring precious Hubble time.

An Astronomical A-Team

Samantha and Dr. Salzer were awarded 25 orbits of Hubble time–5 orbits each of the KISS Green Peas they wanted to observe. To make use of her Hubble time, Samantha assembled an A-Team like no other to tackle the job. First, of course, was Dr. Salzer. Besides already being familiar with the galaxies to be observed due to his work with KISS, Dr. Salzer is, among other things, an expert in extragalactic astronomy generally, optical spectra, emission line galaxies, and surveys. The emission line galaxy expertise and his specific extragalactic star formation experience was particularly useful. This is because of the OIII prominence in Green Pea spectra and their connection to extreme star formation.

Next, she invited Professor Danielle Berg of UT Austin to join the team. Professor Berg is an expert at working with COS data and UV data in general. Samantha had met Professor Berg when she gave a colloquium at Indiana University about COS while she and Dr. Salzer were writing their second Hubble proposal. They knew Professor Berg’s expertise would be invaluable in helping them decode the data from COS, so they invited her to join them.

Finally, Samantha recruited Professor Aparna Venkatesan of the University of San Francisco. Professor Venkatesan is a theorist specializing in how ionizing radiation escapes galaxies and interacts with the mediums it encounters. Samantha had also met her before as she was a collaborator of Dr. Salzer’s, but Samantha had never had the opportunity to work with her prior to this project. She and Dr. Salzer knew that including Professor Venkatesan would allow them to attack the question of how ionizing radiation escapes from observational standpoints and theoretical and modeling perspectives. 

Eyes on the Sky and Eyes on the Future

With her powerhouse trio, Samantha is currently unlocking the extragalactic secrets encoded in the UV spectra from COS. Many questions remain about the Green Peas. These questions include questions about their structure, the spatial nature of their star formation, why the OIII emission dominates, and their appearances in the cosmological present. For now, though, Samantha and her team are focusing primarily on how the UV ionizing radiation escape rate changes related to the masses, emission line strengths, and star formation rates of the Green Pea galaxies. As of this article, the team still has only gotten observations for four out of five of their galaxies. Therefore, they’ve got lots of work before they get a clearer picture of the KISS Green Peas.

However, you can stay tuned for glimpses of their Hubble research (and other ground-breaking Hubble research). You can do this by following @spacetelelive and @nasahubble on Twitter for sneak peeks into what they’re studying before they release their findings.

The post Green Pea Galaxies | More Than Just a Photographer of Pretty Faces appeared first on Space Tonight.

I met Laura during the fall of my junior year of my undergraduate career with Indiana University studying Astronomy. Back then, she was a first year graduate student in the astronomy department…rarefied air for astronomy enthusiasts in an era where increasingly, there were more astronomy students than graduate positions available. A self-proclaimed extrovert, I naturally introduced myself to her like I had to many of the other department members and found that we had several interests in common besides the obvious love of things beyond the Earth’s atmosphere. The department had always been a close-knit one, so like with Laura, I had easily gotten to know many of my peers, professors, and graduate students. Because of this close-knit relationship between members of the department, it had always been fairly easy to celebrate the success of others. As such, one day, while casually browsing through some department news, I saw that Laura had been awarded time on the VLA. To think that someone not that much older than myself could successfully solicit time from a well-known telescope was mind-blowing. I reached out to Laura, hoping to learn all about her opportunity first hand, and she thankfully agreed to share about her work and experiences.

First things first, you may be wondering: what is the VLA? In the astronomical community, it is a well-known telescope, but to the general public, maybe not so much. For those in my audience who are unfamiliar with the VLA, the VLA is a radio telescope in Socorro, New Mexico–little more than an hour from the New Mexican metropolis of Albuquerque. Despite its identity as a telescope, if a casual observer were to happen upon the VLA, they might not recognize it as a telescope. For one, the VLA doesn’t look like the telescope of your average backyard astronomer. There’s no long optical tube, no tripod, and definitely no eye piece. Rather than looking like a classic optical telescope, the antenna of the VLA are more like old-fashioned radio dishes literally a la the 1997 science fiction film Contact. But that’s not the only way the VLA doesn’t look like a classic telescope. As hinted at by my use of “radio dishes” in the plural, the VLA isn’t just one radio dish: there are actually twenty-seven radio dishes total arranged in a y-shaped configuration…hence the name, “array”. These twenty-seven radio dishes can be moved closer or farther apart with a minimum array size of about 1 km across and a maximum array size of about 36 km across. The combination of many radio dishes plus the size of this array effectively makes the VLA one giant telescope. This is in stark contrast to most modern telescopes as many telescopes around the world are mere meters across. This greater telescopic “diameter” of the VLA allows for a better resolution of astronomically small objects which is incredibly important given the types of galaxies in Laura’s sample.

Laura’s VLA sample was primarily gas-rich dwarf galaxies in the local universe. This description means that these galaxies have lots of neutral atomic hydrogen, are smaller than normal galaxies, and are within 5 Mpc (or for a more digestible unit of distance, roughly 16 million light years) of the Milky Way galaxy. For her graduate research, she chose to do a multiwavelength study of 45 such galaxies to analyze the correlation between recent star formation and turbulence in the interstellar medium (ISM). To do this, she has to study the neutral atomic hydrogen–or HI (pronounced “H one”), as astronomers call it–and its movements because HI is considered a marker of a region’s potential to form stars due to HI clouds being reserves of material for active star formation.

This is where the VLA comes in. In astronomy, it is common knowledge that different ions and molecules emit light at different wavelengths. HI emits light at the wavelength of 21 cm which is in the radio part of the electromagnetic spectrum. Since 21 cm is within the  VLA’s wavelength range, this makes the VLA well suited for observing HI clouds. In order to study the turbulence of the HI, Laura and her collaborators created 2-dimensional images called moment maps. The 0th moment is a map of where the HI is in the galaxy. The 1st moment is a map of how the HI in question is moving. The 2nd moment is a map of the velocity dispersion of the said HI. If the idea of ‘moments’ is confusing, think of this simple analogy from basic physics: The 0th moment is similar to displacement. As we learn in basic physics, displacement quantifies how far an object is from the origin of the reference frame the object in question exists in. Similarly, the 0th moment shows where HI is in the galaxy in question…though it also shows how much HI there is in different parts of the galaxy. For the 1st moment, the analogy is more direct. The 1st moment is like the physics concept of velocity. Where velocity quantifies the rate of change of position for any object, the 1st moment similarly quantifies the rate of change of position for the HI in a galaxy. The 2nd moment, however, does not have such an easy analogy as the 0th and 1st moments. However, given that the 2nd moment corresponds to velocity dispersion, this means that the 2nd moment refers to how much the velocity of the HI changes from the average velocity of the gas at a specific location in the galaxy.

Now, why study these pint-sized galaxies? If you’ve ever had the pleasure of gazing upon images of dwarf galaxies, you’ll know that they often don’t look nearly as photogenic as their gigantic cousins and that trying to locate them in scientific images is like playing a cosmic game of Where’s Waldo?. However, as it turns out, smaller galaxies have an incredibly important property that aids in studying the events surrounding star formation: solid body rotation. Solid body rotation is like riding a merry-go-round. If you and your best friend were sitting on a merry-go-round at different distances from the center, you would rotate at different speeds, and if you and your friend were also in a straight line, you would remain in that straight line. Solid body rotation therefore allows the different parts of an object to rotate together as one unit. This has important implications for studying the events of star formation in galaxies. When things rotate–especially things that aren’t solid–mixing of constituent materials often is involved. Star formation generally happens over cosmologically short time scales, and when mixing happens, regions with different star formation histories inevitably mix together. Like mixing milk into tea or creamer into coffee, it becomes harder and harder to separate out the different components of the mixed region as mixing happens. While not usually problematic when studying galaxies globally, when studying localized regions of galaxies as Laura and her collaborators do, this becomes a problem very quickly. Fortunately, solid body rotation minimizes this mixing and thus makes it easier to sleuth around a galaxy and figure out what happened.

While her current research project is still ongoing, Laura has many aspirations for the potential of her project. Her primary aspiration for the project is that it will shed more light on the evolution of galaxies. She hopes that by understanding the connections between star formation and turbulence, astronomers will be able to understand on what time scales star formation adds energy to the HI reserves of a galaxy. In addition, since stellar feedback (i.e. supernovae, hot stellar winds from post-main sequence stars) is thought to be a primary driver of turbulent motion in the ISM, she hopes to also contribute to the understanding of how stellar feedback affects the ISM. By understanding these processes, astronomers will be able to make better models of galaxies and their inner workings. However, regardless of whatever she and her collaborators end up discovering about the intra-galactic turbulence, we will be one step closer to understanding how this universe we live in works.

The post Hunting Down Correlations Between Star Formation and Gas Turbulence: The Thesis Work of Laura Congreve Hunter appeared first on Space Tonight.

The observable universe, the part of the universe that we can see, is approximately 93 billion light years in diameter. This means that the distance between us and the edge of the observable universe is about 46.5 billion light years in any direction.

What is the “observable” universe?

Now, some of you may be wondering, what is the observable universe and how does this answer the original question? The observable universe is the only part of the universe that we have access to; beyond it is more of the same, but we cannot see it because light has not had enough time to reach us from those great distances.

Not only this, but the universe is expanding, which adds a further complication to the definition of “observable.” Any question about the size of the universe can really only be answered in terms of the observable universe, at least with any hope of accuracy.

Before we delve into a discussion of how the size of the universe was determined, we have to talk about some basic assumptions in cosmology. First of all, it is important to know that the speed of light in a vacuum is constant. This is key to the definition of cosmic distances; one light year is the distance light can travel in one year.

Secondly, the idea that the universe is expanding is crucial to determining the size of the universe. As was discussed in our look into dark energy, Edwin Hubble determined that distant galaxies are moving away from us. His observations and ones that followed lead to the realization that the universe is expanding.

The last thing to know is that the rate at which the universe is expanding is increasing. Originally discovered in the late 20th century, scientists realized that the universe isn’t just expanding, it’s accelerating its growth. 

What is the distance to the edge of the universe?

Now that we have the tools to solve the problem, how do we determine the size of the universe? In order to understand the size of the universe, its critical to distinguish between the concepts of proper and comoving distances.

The proper distance between two objects in space is a measurement of their separation at some instant in time. This is the definition of distance that you are familiar with, but there is a slight complication. Since light travels at a finite speed, we can never know the actual distance to a moving object in the instant we observe it. This is because light takes time to travel from a source to us, and in this time, the source may have moved. This means that the proper distance of an object can never be observed, but it can be calculated.

The comoving distance between two objects is one that takes the expansion of space out of the equation. In a static universe, where nothing is in motion, the comoving distance and the proper distance would be the same, since there would be no expansion to account for. In our universe, however, the relationship between the constant comoving distance and the proper distance is a quantity known as the scale factor. This value changes over time to account for the variable rate of expansion of the universe. Currently, this scale factor is equal to 1. Therefore, right now, the comoving distance and proper distance are the same. 

If you are confused, that is completely understandable! They are both hard to visualize;  the comoving distance is a purely cosmological measure of distance, and the proper distance is impossible to actually see. The really confusing part is that the distances to everything we can see, from the Moon to the most distant galaxy, are facades of the actual distance. As mentioned previously, it has to do with the speed of light in combination with the expansion of space. To clear up this ambiguity, we will look at a brief example.

The most distant objects we can see are about 13.4 billion light years away. Except they aren’t actually; they are much farther away. The light from those objects traveled for 13.4 billion years, which in a static universe would mean the proper distance of the objects was 13.4 billion light years, since they could not have moved as the light traveled to us.

However, given that our universe is not static, the light left those objects when they were much closer to us, and that light took 13.4 billion years to reach us through continuously expanding space. In other words, the light left when the objects were much closer to us than they are now, but the space through which it traveled expanded to 13.4 billion light years across as it traveled through it. This gives us the illusion that the objects are 13.4 billion light years away. 

In reality, these objects are much farther away: about 32 billion light years according to the latest cosmological models. Their proper distance when the light left them was much smaller than 13.4 billion light years and now it is 32 billion light years.

Therefore, the distance to the edge of the universe appears to be approximately 13.8 billion light years, but its proper distance is actually about 46.5 billion light years.

How are these different types of distance determined?

To put these varying definitions of distance into more concrete terms, it would be as if someone threw a ball at you, and as they threw it, the space between you and the person throwing it grew. As it grows, the ball takes longer to reach you, and the person ends up being much farther away from you than when they threw the ball.

The only problem with this analogy when compared to the situation with the most distant objects is that the speed of light is the cosmic speed limit. It is the speed at which information is transmitted to us, and nothing can go faster (as far as we know).

Therefore, it would be as if the person throwing the ball was invisible and we could only determine where they were based off of the ball. If we didn’t realize space was expanding, we would assume the person was much closer than they really were, just like the illusion created by the most distant objects in the observable universe. 

So, how do we determine how far the light from any object has traveled? The short answer is by using the Doppler effect. This effect, which you might be familiar with, is what explains the change in the pitch of the siren on an emergency vehicle as it drives past you.

As it speeds towards you, its pitch increases, and as it goes away from you, the pitch drops. This is due to the velocity of the vehicle causing a shift in the frequency of the sound wave. Motion towards you causes the frequency to increase and motion away causes it to decrease. The same effect happens with light.

A distant galaxy that has some sort of recessional velocity due to the expansion of the universe will emit light that gets redshifted as it travels to Earth. This term “redshifted” refers to the decrease in the frequency of the light as caused by the Doppler effect. Since red is the lowest frequency of visible light and blue is the highest, we use the terms redshifted and blueshifted to describe the change in frequency. 

But, how do we know the frequency is shifted? Using a spectrograph, which breaks down the constituent wavelengths in light to reveal the composition of a source, scientists can find a specific signature of an element and match it to those in a distant object.

They measure the frequencies of the same element in the laboratory, where it is at rest with respect to the spectrograph. Then, when they compare this measurement to the one taken from the distant object, they can determine how fast the object is moving away from us. 

Using this information, in combination with Hubble’s law, which tells us that the distance to an object and its recessional velocity are directly related, we can determine how far the light had to travel, and, from this, calculate the age of the observed object. 

In fact, you might be wondering why there is such a large difference between the proper distance of the most distant visible objects and the edge of the universe as compared their apparent distances. This is due to the Doppler effect; for instance, an object 13.2 billion light years away is much less redshifted than one 13.3 billion light years away.

What is beyond the edge of the observable universe?

Perhaps the most mind-boggling implication of current cosmological models is that there are objects in the universe that we will never be able to see. We know that the proper distance to the edge of the observable universe is about 46.5 billion light years. We also know that it is rapidly expanding. In fact, objects that are currently beyond 13.8 billion light years (give or take a few million) away right now have a recessional velocity greater than the speed of light. 

Wait a minute. Isn’t the speed of light supposed to be the cosmic speed limit? Yes. It still is; these objects aren’t moving away from us at that speed, its just that the space between us and them is expanding so fast that it appears that they are.

Try not to mistake traditional translational velocity with the expansion of space; this is critical to understanding the “mind-boggling” part. In other words, there is a difference between an object being propelled to velocities at or above the speed of light and the distance between two objects increasing at a similar rate due to the expansion of space. The former violates the laws of physics, the latter does not.

Objects that are so far away that space is expanding faster than the speed of light lie outside of what is called the Hubble sphere. This sphere has a radius of 13.8 billion light years, which exactly corresponds with the age of the universe.

As mentioned before, many objects, particularly those that appear near the edge of the sphere, actually now lie outside the sphere. That is, their proper distance is much farther than the edge of the sphere. It’s just that the light from their distant pasts lies inside of it.

So, objects that lie outside the Hubble sphere reside in space that is expanding at a superluminal rate (faster than light). The crazy part is that light leaving these objects right now will eventually fall within the Hubble sphere and then be visible from our part of the universe (after traveling a long time, of course). 

Eventually, when the universe expands to a radius of about 62 billion light years, we will reach what is called the cosmic event horizon. This means that light emitted from objects beyond that distance will never fall inside of the Hubble sphere. This is because the space between the object and the edge of the sphere will be expanding too fast for it to reach the edge. In other words, we will never be able to see these objects. Consider yourself sufficiently “mind-boggled.”

An even more intense consequence of the expansion of the universe is that at some distant point in the future, even the closest objects to us will be so distant that they will be moving away faster than light. This means that eventually, all of our galactic neighbors may be invisible to us (assuming there is still an “us” at that point). Not to worry, of course; according to our current understanding of cosmology and dark energy, this won’t happen for a long time. 

Clearly, understanding the size of the universe is not as simple as you might have originally thought. The universe is full of unintuitive and mysterious phenomena, and the edge of it is no exception. In dealing with the immense size and time scales that come up frequently in cosmology, it is no wonder that we find ourselves as a species to be, at best, a small and insignificant part of something much grander. 

The post How Big is the Universe? appeared first on Space Tonight.

A black hole is a source of gravity so strong that nothing, not even light, the fastest thing in the universe, can escape. More formally, a black hole is a singularity (or “tear”) in the fabric of spacetime itself. They are some of the most mysterious and paradoxical phenomena in the universe. To this day, there is a great deal that scientists do not know about black holes.

What is the history of black holes?

Black holes originated from the field equations of Einstein’s theory of general relativity in the early 1900’s. Initially, they were just a mathematical phenomenon (solutions that cause a zero denominator) in the equations. However, in the years that followed, scientists began to theorize that if a star with a sufficiently large mass died, it would crush its entire mass down into a singularity.

A singularity is the beating heart of a black hole. It is a point in space as small as an atom that contains an extreme amount of mass; some black holes are many times the mass of the Sun. The implications of an object with this property were mind-boggling. Not only would it be an object of immense gravitational pull focused at a small point in space, but it would also be powerful enough to prevent light from escaping it. Due to this, it would be completely invisible to any observer, hence its name. 

Scientists also began to discover some important properties of black holes, such as their size and the mass of a star required to create one. The former prediction implied that there would be an event horizon, a spherical boundary around the singularity through which light cannot escape. The latter determined that only the most massive stars could collapse into a black hole. 

Another key discovery about black holes was made in the 1970’s, by the late theoretical physicist, Stephen Hawking. He claimed that black holes were not immortal, as they were originally thought to be. Hawking showed that black holes slowly leaked radiation off of their event horizon that caused them to lose mass at an increasing rate over time. This quantum phenomenon became known as Hawking radiation and is now a crucial factor in determining the future of the universe. 

In the 1960’s, astronomers detected a strong source of x-rays from a star in the constellation Cygnus. This source was eventually determined to be the first black hole discovered by humans. The black hole was named Cygnus X-1 and is a black hole of about 15 times the mass of the Sun. The system it belongs to is about 6000 light years away from Earth.

Even more recently, in 2019, astronomers working at the Event Horizon Telescope (EHT) announced that they had successfully photographed a supermassive black hole in the center of a large elliptical galaxy over 55 million light years away. This black hole is much larger than Cygnus X-1, with an estimated mass of about 6.5 billion times the mass of the Sun. Although the image without context is unimpressive and blurry, it is the first of its kind and provides visual evidence that black holes actually exist.

What are some properties of black holes?

Black holes are the remnants of once bright and massive stars. As these stars begin to run out of fuel, they collapse in on themselves until the element iron is fused. At this point, the science behind nuclear fusion (the smashing of atoms together) dictates that the star begins to lose energy. In other words, up until iron, for every element fused, the star gains energy. But, as soon as iron is reached, the star no longer makes profit on the energy required to fuse it together. So, the star which has been burning for millions of years, quickly loses the battle against gravity. The outer layers collapse in on the dead core of the star at such a rapid rate that a singularity, and thus a black hole, is formed.

One of the prominent properties of black holes that scientists have predicted and observed is the way black holes interact with other matter. Specifically, when black holes “eat” matter, some of it does not fall into the hole and instead orbits around it. Eventually, this extra highly energetic matter forms what is called an accretion disk around the black hole. Scientists predict that this kind of disk is common in systems containing a black hole and one or more stars. The black hole slowly feeds off of the matter in the outer layers of the companion stars, creating an accretion disk of hot gas and dust.

Black holes come in all different sizes. Their size depends heavily on the mass of the star that collapsed to create it. However, scientists have discovered black holes with masses much greater than any one star. They have concluded that black holes can grow if they encounter one another. This type of interaction is predicted to be part of galaxy formation, as the center of galaxies is the perfect place for black holes to run into each other. Black holes of this type are called massive and supermassive black holes, depending on their mass.

Supermassive black holes at the center of galaxies seems to be an ordinary thing in the universe. Scientists now believe that there is one in the center of every galaxy; they may be a requirement for galaxies to form. The Milky Way is no exception. Astronomers have detected radio signals coming from the center of our galaxy in the constellation Sagittarius, which is an indicator of black hole activity. This, in addition to the sporadic and rapid movement of stars in the nucleus of the Milky Way, seems to point towards the existence of a supermassive black hole in the center.

What would happen if you fell into a black hole?

One of the most important consequences of Einstein’s theory of general relativity is the effect gravity has on the passage of time. General relativity says that the presence of mass or energy causes spacetime to curve, which in turn tells other masses how to move. The key takeaway from this definition is the idea that gravity not only manipulates space, but time too. Essentially, the more powerful the gravitational force on an object, the slower it’s time moves relative to some other object that’s at rest (or close to rest, like the Earth). 

Does this mean that a person near a black hole moves in slow motion? Well, close, but not quite. You see, for that person, a second feels like a normal second, but compared to an observer on Earth, they would find that for each one of those seconds near the black hole, much more time on Earth has passed. Can you use black holes to travel through time? The quick answer is sort of. One of the fundamental principles of Einstein’s theory is that while time can be slowed and sped up, it cannot be reversed. In other words, while you could travel to the future by slowing down your time relative to Earth, you cannot go to the past. Believe it or not, this is not even the strangest aspect of a journey to a black hole.

If you find yourself passing through the event horizon of the black hole, it will appear to anyone watching your perilous adventure that you are frozen on the boundary of the hole. Perhaps even crazier, in your point of view, you will watch the entire lifetime of the universe play out in front of you in a single instant. You will see everything happen that will ever happen, all at once. As far as what happens inside the black hole, there is no way to know for sure, at least not yet. Since we know of nothing that can travel faster than light, there is currently no way for scientists to probe inside of a black hole and look at the singularity.

Another consequence of the immense gravitational pull of black holes is that any object close to the event horizon will stretch out to unimaginable lengths. This process is often referred to as “spaghettification”. Each unit of distance closer to the event horizon corresponds to an inordinate change in the strength of the local gravity. It would be like if the gravity on the second floor of an office building was half of the gravity on the first floor. 

Due to this stretching and the science behind general relativity, the stretched object would also appear to get redder in color. The source of this color change is the Doppler effect, where the wavelengths of light reflecting off the object change after they pass through the gravitational field of the black hole. Unfortunately (or maybe fortunately), any human astronaut caught up in the pull of a black hole would almost certainly pass out and die before they even got close to the event horizon. The g-forces one would experience as they got close would be thousands to millions of times the livable amount. Thankfully, there are no black holes near Earth, so we are safe for now.

What do black holes tell us about the universe?

I mentioned earlier that Hawking radiation, which causes black holes to die slowly, helps scientists determine the future of the universe. While there are an enormous amount of basic factors to take into account, physicists predict that the universe will eventually be entirely composed of black holes and stray particles of light. In fact, the universe will likely live most of its lifetime without any matter; all the stars, planets, and nebulae in the universe will live and die in only a small fraction of the entire lifetime of the universe. 

Perhaps even scarier, eventually these black holes will die and the universe will slowly become a great void of nothingness. However, the fate of the universe could end up being drastically different than this if even a few of the assumptions scientists make are wrong.

Some physicists predict that black holes are just passageways to other parts of the universe and that all of the matter that they eat is tossed out the other end at some “white hole.” There has been no evidence to support this, but our knowledge of black holes is so limited, so we cannot discount it. Almost more fantastical is the claim by some that black holes lead to other universes entirely. One thing is certain: understanding the paradoxical nature of black holes could answer important questions we have about the fate of the universe and our existence in it. 

The post What is a Black Hole? appeared first on Space Tonight.

Galaxies are gravitationally–bound systems of stars, nebulae, interstellar dust, gas, and dark matter. There are countless galaxies in the universe, all different ages, sizes, and types. And, on average, each of these galaxies contains billions upon billions of stars and planets. At this immense scale, the universe seems unfathomable and infinite. However, scientists have learned a lot about galaxies, from the closest ones to those at the edge of the observable universe. Despite their vast knowledge, like many scientific endeavors, scientists have discovered more questions than answers about the cosmos. 

How were galaxies discovered?

The term “galaxy” comes from the Greek word galaxías, which means “milky”. Since galaxies were thought to be similar to our own, the Milky Way, it made sense to name them accordingly. The Milky Way’s name comes from its appearance in the night sky, as if someone spilled milk across the sky. 

Up until the turn of the 20th century, scientists did not know that galaxies existed. Although some of the larger and closer galaxies were charted by astronomers, they were classified as nebulae, clouds of interstellar gas in which stars are born. In fact, in the 18th century, Charles Messier, known for his catalogue of these types of objects, called the first galaxies he saw in his telescope “spiral nebulae.” Unbeknownst to him, these mysterious objects were much larger and farther away than regular nebulae.

By the early 1900’s, developments in astronomical techniques enabled astronomers to determine the distances to these “nebulae.” Because of this, the idea of what we now know as a galaxy was born. Due to the uncertainties in the calculations of these distances, some still argued that these spiral nebulae were inside our own galaxy, the Milky Way. However, an American astronomer, Edwin Hubble,  accurately determined the distances to a number of nearby galaxies, thus solidifying the idea that they were well beyond the Milky Way. 

What are the different types of galaxies?

Galaxies are classified by what is known as their morphology. There are three main morphological types: elliptical, irregular, and spiral. Each of these classifications has sub-classes, such as “barred” for spiral galaxies. In addition to the four main types, there are dwarf galaxies, which actually account for most of the galaxies in the universe. Dwarf galaxies can be classified as elliptical (sometimes called spheroidal), irregular, and spiral. Other types of galaxies include lenticular, peculiar, and ultra-diffuse, among others. 

The types, as you might expect, were originally developed to correspond with the appearances of the galaxies. Irregular galaxies look like a randomly distributed cloud of stars and gas. Elliptical galaxies, unsurprisingly, look like ellipsoids. Spiral galaxies, probably the most well-known type, have spiral arms and a central nucleus. Dwarf galaxies are similar to the other types, but, as their name suggests, they are much smaller in overall size. Lenticular galaxies are often classified as a cross between elliptical and spiral galaxies.

In terms of differences between morphological types, there is more than just shape and size. One of the main differences between the classes is their overall stellar composition and age. In general, elliptical galaxies have older, redder stellar populations, whereas irregular galaxies usually have younger, bluer stellar populations. Spiral and lenticular galaxies lie somewhere in between; spiral arms are sources of star formation, whereas nuclei contain older stars. 

How do galaxies evolve?

Another important part of morphology is galactic evolution. Initially, astronomers thought that elliptical galaxies evolved into spiral and lenticular galaxies. We now know that this is not correct. Today, there are two opposing theories of galactic evolution. The “top-down” or monolithic collapse model, suggests that galaxies as they appear now formed directly from dust and gas. The “bottom-up” or hierarchical clustering model suggests that there were intermediate phases in the size and morphology of galaxies.

The top-down model suggests that all galaxies formed from a universe-wide cloud of dust and gas, just as stars and planets form in star systems. This would explain why stars and globular clusters (large spherical clusters of stars) in the halo of spiral galaxies are older and contain fewer heavy elements than those in the disk of the galaxy. One of the main problems with this is that developments in cosmology have shown that the existence of such a cloud of dust is highly improbable. In essence, this theory does not work with the current model of cosmology.

The bottom-up model suggests that larger galaxies form through the collisions of smaller dwarf galaxies. Essentially, sometime after the Big Bang, the universe formed stars and globular clusters, which coalesced into the first dwarf galaxies. These dwarf galaxies eventually followed suit and formed some of the larger galaxies we see today, even our own. Current evidence points to this model of galactic evolution as being correct, or at least more so than the previous one.

A key principle of astronomy is “look-back time,” which essentially says that the farther you look in space, the farther back in time you are looking. This is a factor of the speed of light being finite; it takes time for the light to get from the object to you. With this in mind, astronomers can see how galaxies evolved over time by simply looking farther away. What they discovered was that galaxies are smaller and less developed the farther they look. This suggests that the bottom-up model is right. The theory also incorporates dark matter, which makes it more compatible with modern cosmology. The theory suggests that the first galaxies began to form about 13 billion years ago. Due to this fact, the bottom-up model is the predominant theory of galactic evolution. 

How do galaxies interact with each other?

As mentioned in our discussion of the bottom-up model of galaxy formation, galaxies collide with one another. We have observational proof of this process, which astronomers often refer to as galactic cannibalism. In fact, evidence suggests that our galactic neighbor, the Andromeda Galaxy, is on a collision course with the Milky Way. Since Andromeda is about 2.5 million light years away, the event won’t start for at least a few billion years—so I wouldn’t worry about it too much! In this type of galactic dance, some stars from the galaxies involved are thrown out into intergalactic space. Fortunately, the odds of stars colliding with one another are slim because of the vast amount of space in between them. 

Galaxies organize themselves according to the large-scale structure of the universe and local gravitational interactions. We know that the Milky Way is part of a local neighborhood of about a few dozen galaxies, succinctly called the Local Group. This group of galaxies is located in the Virgo Cluster, a larger group of around 1000 galaxies, the majority of which lie in the direction of the constellation Virgo. This cluster is on the outskirts of an even larger cluster called the Virgo Supercluster, which is also found in Virgo. The supercluster contains thousands of galaxies and is about 110 million light years across. 

It does not stop there. The Virgo Supercluster is part of a larger galaxy cluster, the Laniakea Supercluster, which is part of the Pisces-Cetus Supercluster Complex, a filament of galaxies. This is one of many filaments that make up the observable universe. These filaments represent the largest type of organized structure of matter that we know of. Each of them contain billions of galaxies, which together form the large-scale structure of the universe, the “cosmic web.” 

Galaxies are a fundamental structure in the universe, just as stars are fundamental in galaxies, and planets in star systems. Overall, the observable universe is about 92 billion light years across, and, as modern estimates suggest, contains more than a trillion galaxies. In other words, there are more galaxies in the cosmos than there are grains of sand on Earth.

The post What is a Galaxy? appeared first on Space Tonight.

The closet planet to the Sun, Mercury, has been observed by NASA in two different ways. The first was the Mariner 10 spacecraft which flew by Mercury three times from 1974 to 1975. This spacecraft took photos of the small planet but captured only half of its surface. This probe’s mission was to fly by Mercury and Venus and was the first time any probe had done flybys of more than one planet. 

30 years passed until we visited the planet again, but this time we stuck around a little longer. The Mercury Surface, Space Environment, Geochemistry, and Ranging spacecraft (commonly known as MESSENGER) began its 4-year orbit of Mercury in 2011 with the mission of observing the planet in depth. MESSENGER has provided us with most of what we know about the planet, including mapping the planet completely. When the spacecraft finally ran out of fuel in 2015, lasting 3 years longer than originally intended, it crashed into the surface of Mercury and created a new crater. 

Mythology

Mercury is named after the Roman messenger god Mercury. In Greek mythology, this god is called Hermes. A prominent trait of this god was his speed, which suits the fastest planet in the Solar System perfectly. Mercury was visible from Earth in the time of the ancient Greeks twice a day, so it was originally thought that Mercury was two different planets. They called the morning planet Apollo and the afternoon planet Hermes. When it was later discovered that the two planets were the same, the name Hermes (or Mercury) was chosen over Apollo. 

Mercury also has a role in astrology. Similar to the messenger god in Greek and Roman mythology, astrology views Mercury as the planet of communication. The style of communication, or “your Mercury”, is determined by where Mercury was at the time of your birth. 

Mercury has had quite an influence on pop culture as well. The planet has acted as a muse for composers like Gustav Holst who composed a movement in his orchestral suite The Planets entitled “Mercury, The Winged Messenger.” It has also appeared as a setting or subject for countless science fiction books, poetry, films, tv shows, and other forms of media.

How big is Mercury and its orbit?

Mercury is the smallest planet in our solar system at a diameter of just 3,032 miles (4,880 kilometers), a little less than the distance from New York to Ireland. Its mass is 1/18 of Earth’s mass, at about 3.3×10²³ kilograms, and has a surface area of 28.88 million square miles. 

While the Earth takes 365 days to complete one full orbit around the Sun, Mercury only takes 88. Mercury is the fastest planet in the Solar System, orbiting the Sun at 29 miles (47 kilometers) per second. Mercury is, on average, 1/3 the distance of Earth from the Sun. Its path of orbit around the Sun is the most elliptical of all the planets which means that its distance from the Sun ranges from 29 to 43 million miles (46 to 70 million kilometers). 

Geology of Mercury

The geology of Mercury is our window into the history of the planet. This desolate planet was not always so bland. In the early years of our solar system Mercury was a geologically active planet. As its core cooled, the surface of the planet contracted to form daunting cliffs and long narrow ridges. The young planet also had volcanic activity which helped form its solid crust. Although all geological activity ceased about 3.5 billion years ago, the core of the planet, which is about the size of our moon, is said to still be partly molten. 

There are theories about why Mercury’s core is so large in comparison to the other inner planets. Some think that the crust of the planet was originally much thicker but was destroyed by impacts from very large celestial bodies early in its life. Others think that the young Sun may have stripped it of its outer layer with violent solar wind. 

Now, the most abundant surface feature on the planet are thousands of impact craters. These craters are up to 68 miles (110 kilometers) in diameter. These craters can be much larger than those found on other terrestrial planets because Mercury does not have a thick, protective atmosphere. 

What would it be like to live on Mercury?

Mercury’s absence of a developed atmosphere causes a few problems when it comes to habitability. First, and most important, you cannot breathe on Mercury as there is only a thin layer of hydrogen, helium, and oxygen. Second, without a thick atmosphere, the planet cannot regulate its heat. At night, the temperature gets as low as -300 degrees Fahrenheit (-184 degrees Celsius) and during the day it reaches 800 degrees Fahrenheit (427 degrees Celsius). These intense temperature changes and lack of breathable air make living as we know it on this planet impossible. 

Other aspects of life on Earth, like seasons and length of a day, are also different on Mercury. Seasons, like summer and winter, are caused by the tilt of a planet’s axis of rotation. Mercury’s axis only tilts by 2 degrees, compared to Earth’s 23.5 degrees, so technically it shouldn’t experience seasons. However, since Mercury’s orbit is so elliptical, there is a form of summer and winter. Unlike the predictability of seasons on Earth, Mercury moves so fast in its orbit that it is hard to tell when one season ends and the other begins. There is also some form of weather beyond just hot and cold days. Usually the magnetic field of a planet will protect it from solar radiation, but Mercury does not have a very strong one. When its magnetic field fails, tornadoes of solar wind plasma, a gas-like substance, spiral down to the surface of the planet. Unfortunately, these tornadoes don’t lead to Oz. 

Have you ever felt like the day drags on forever? On Mercury, it certainly does. One day-night cycle, a solar day, on Mercury lasts for 176 Earth days. The planet’s solar day lasts so long because the planet is moving on its orbit as well as spinning on its axis. It only takes the planet 59 days to spin on its axis, known as a sidereal day. Once it has completed a sidereal day, the planet must further rotate to face the Sun again for a solar day to be completed. This would mean that the Sun would rise and set twice during one Mercury day. Maybe two sunrises a day doesn’t sound too bad but, on this planet, the Sun is 3 times larger and 7 times brighter than it appears on Earth.  

What is it like to stand on Mercury? Mercury is gray and dusty, like our moon. During its long nights, it would be incredibly dark due to the absence of any moons. Mercury has a little over a third of Earth’s surface gravity. This means if you weighed 100 lbs on Earth, you would way a little over 33 lbs on Mercury. It also means that if you jumped off a chair on Mercury, you would fall two thirds slower making for a much gentler landing. 

There is some evidence for water on Mercury. Evidence found by the MESSENGER spacecraft suggests that there is some scarce water in the form of ice. The adjacent image shows highlighted spots on the north pole of Mercury where water ice is speculated to be found. The quantity and form that the water is said to be in is not sufficient enough to survive on. That being said, if there was any place to live on Mercury, this pole would be it. 

The Future of Exploring Mercury

As of now, there are no plans of visiting Mercury within the next 5 years. Since Mercury is uninhabitable and geologically inactive, scientists might be aiming up and out to learn more about other mysterious aspects of our solar system and universe. 

The post Mercury: the Ultimate Guide appeared first on Space Tonight.

Dark energy is a concept in modern cosmology that is best defined as the intrinsic energy in empty space, or “vacuum energy.” This energy contributes to an outward pressure that causes space to expand. In turn, the expansion creates more space, which then creates more dark energy, and thus expands space further and faster. This paradoxical interaction in which energy is seemingly created out of nothing is what scientists theorize is responsible for the accelerating expansion of the universe. 

How did the idea of dark energy come to be?

The history of dark energy originates with Albert Einstein’s famous general theory of relativity. The theory is the most accurate descriptor of gravity and its functionality. It accomplishes this feat through what are known as the Einstein field equations. These equations explain that gravity is the effect of massive and energetic objects curving the fabric of space (and time).

In 1917, after Einstein first developed the equations, he included an additional term called the cosmological constant. The sole purpose of this constant was to ensure that the equations described a static universe. We now know that the universe is not static; it was created in a massive explosion, the Big Bang. This term now represents dark energy, as seen in the image below.

Einstein, however, formulated the field equations before the Big Bang theory became the prevalent theory of the origins of the universe. Therefore, the cosmological constant was initially meant to act as an outward pressure, or “negative gravitational force” in empty space, thus preventing massive objects from crushing space in on itself. Einstein calculated the constant in such a way so that this outward pressure would only be enough to keep the universe from changing size. 

In 1929, Edwin Hubble, an American astronomer for whom the famous space telescope is named after, discovered that galaxies outside our own were moving away from us. He noted that the farther away the galaxy was, the faster it was moving away. This indicated to Hubble and the scientific community at the time that the universe was expanding. To clarify, consider for a moment that the universe is a chocolate chip cake with chips representing galaxies. When the cake is baked in an oven, it expands. Each chocolate chip moves away from the others as the space between them expands.

This is exactly what happens with the universe; the space between galaxies expands, with the effect being that the farther away a galaxy is, the faster it is moving away from us. Hubble formalized this principle in what is now known as Hubble’s law. 

After Hubble’s discovery, Einstein retracted the idea of the cosmological constant and considered it one of his biggest blunders. From then on, it was accepted that the constant had a value of zero. However, in 1998, Einstein’s supposed blunder became relevant once again when scientists discovered that the rate at which the universe was expanding was accelerating. His idea of vacuum energy was the perfect explanation for an accelerating universe. Since then, scientists have calculated a positive, non-zero value for the cosmological constant to reflect the principle that empty space has energy. 

Why is understanding dark energy so important?

Why is solving the dark energy mystery so critical in modern science? Recent studies of the cosmic microwave background radiation have revealed the mass and energy content of the entire universe. Scientists believe that about 70% of the entire universe is made up of dark energy. Only around 30% of the universe is matter, and about 70% of that figure is dark matter.

Therefore, every galaxy, star, planet, and nebula only account for about 5% of the makeup of the universe. That alone should reveal why it is crucial to modern science that we understand what dark energy is and whether or not it actually exists. 

Dark energy will dictate the fate of the universe. If the cosmological constant has a positive value, then empty space has a positive energy density and therefore exhibits an “anti-gravitational” outward pressure on the universe, causing it to expand. As space expands, more space is created, and therefore the universe has more dark energy with which to push out on itself.

The cosmological constant may not be a constant; this type of dynamic dark energy is often referred to as quintessence. If this value increases over time, then the expansion will accelerate infinitely, and we are left with a “run-away” universe, which will expand until planetary systems and even subatomic particles rip themselves apart; this scenario is commonly known as the Big Rip. If the expansion slows to some constant rate, then objects will move away from each other until they cannot see each other and galaxies are left on their own, isolated from the rest of the universe; this is the Big Freeze.

If the expansion completely stops, then, depending on the critical density of the universe, everything may collapse in on itself in a “reverse Big Bang,” called the Big Crunch. Understanding the eventual fate of the universe depends greatly on our understanding of dark energy. 

Unfortunately, as was the case with dark matter, dark energy is not a perfect theory. While it works perfectly in the field equations, it does not match up with the value for vacuum energy predicted by quantum field theory (QFT). This theory is the modern model of quantum mechanics, a branch of physics that deals with atomic and subatomic interactions.

The Einstein field equations and general relativity as a whole are a classical theory; it does not take quantum theory into account. The discrepancy between a quantum and a classical theory can be seen in the difference of the prediction made by QFT and the cosmological constant. The quantum value is about 10¹²⁰ times larger than the value given by Einstein’s equations. This extreme difference has been dubbed by physicists the “worst theoretical prediction in the history of physics.” 

So, the value is wrong, does this mean that dark energy is not real? Not necessarily. It is quite possible that the field equations need revision to include quantum mechanics, but this does not mean that the cosmological constant and the idea of dark energy would be removed entirely. Perhaps a greater problem for the existence of dark energy lies in our fundamental understanding of gravity. 

General relativity, although the most accurate model of gravitation, does not explain what gravity is, only how it acts. The Standard Model of particle physics, one of the greatest achievements of quantum mechanics, dictates that there must be a force carrier particle, or boson, for each fundamental force in the universe. For the electromagnetic force, the boson is the photon, commonly known as a particle of light.

The boson for the strong nuclear force, the force that binds protons and neutrons together in atomic nuclei, is the gluon. For the weak nuclear force, the force that is responsible for the radioactive decay of atoms, the force carrier particles are the W and Z bosons. Scientists have not discovered the boson for gravity, but it is hypothetically known as the “graviton.” The discovery of this particle will provide valuable insight into the mysterious behavior of gravity. 

As was discussed regarding dark matter, gravity may work differently on large scales, perhaps due to the strange quantum behavior of the theorized graviton. It may be that some gravitational interaction on the distance scales as large as those seen between galaxies is what causes the accelerating expansion of the universe. In order to properly unveil the mysteries of gravity, it will likely require a revolution in quantum mechanics. Such a revolution would undoubtedly provide us with insight into the mystery of dark energy and unveil some of the deepest secrets of the cosmos.

The post What is Dark Energy? appeared first on Space Tonight.

Our solar system is just one of the billions of solar systems that make up the Milky Way galaxy. The Milky Way is a spiral galaxy and the “arms” of the spiral are active star formation regions. We are located near the Orion Arm, or the Orion Spur. This spur is between two more prominent arms of the spiral, Sagittarius and Perseus.  

Our solar system is made up of many objects, much more than just planets and moons. The most massive thing in our solar system is the Sun, consisting of over 99% of the Solar System’s mass. The last percent is made up of all of the planets, their satellites and rings, comets, asteroids, and dust combined.

What is a Solar System?

A solar system is one or more stars that have a celestial object(s) orbiting and bound to them by gravity. Solar systems don’t all look like ours. Some systems have multiple stars which orbit around their center of mass. Some star systems only have one planet where others may have many more than ours. The planets from star systems other than ours are referred to as exoplanets. Since other stars are so far away, it is hard to observe the nuances of their systems. But scientists are working hard to discover new solar systems, especially ones with planets that might be habitable for humans. 

The Discovery of Our Solar System

Theories about our solar system date back to the ancient civilizations. There were many ideas about what the Solar System contained, how it was structured, the cosmos etc. Some thought that the Sun, planets, and other stars revolved around Earth. This idea is called the geocentric model and was widely accepted as correct in the second century and beyond. It wasn’t until the 16^th century that the correct heliocentric model, where the planets revolved around the Sun, was accepted. 

The discovery of most of the planets in our solar system was rather arbitrary. Obviously, we have known about Earth for some time now. But we have also known about some of the other planets in our solar system for just as long, we just didn’t know they were planets. To the unaided eye, planets are very bright and look like big stars. But if you track them, as the ancient Greeks did, you will find that they don’t behave like stars. Stars “move” according to where our planet is in its orbit, this is why you can see some stars in the winter that you can’t in the summer. The Greeks found that 5 stars in particular were not changing with the season but rather exhibiting some strange behavior. These were called wanderers, along with the Sun and the Moon. Where stars moved uniformly, the wanderers appeared to periodically slow down, stop, and even change direction. They are Mercury, Venus, Mars, Jupiter, and Saturn.

What about Uranus and Neptune? They are the two planets furthest from the Sun which is why they are very difficult to see with the naked eye. The other objects in our solar system are too small to see unaided which is why more of our solar system was discovered after telescopes were invented in 1608. In 1781, Uranus was discovered by Sir William Herschel. In 1801, the asteroid belt was discovered by Giuseppe Piazzi. Then in 1846, Neptune was discovered by John Couch Adams. 

Origin of Our Solar System

The formation of the members of our solar system started about 4.5 billion years ago. Everything in the Solar System formed from the solar nebula which originally was a spherical cloud of dust and gas. The solar nebula was composed mostly of hydrogen and helium, which are now the two most bountiful elements in our solar system. The nebula collapsed into a spinning disk which then condensed to form the Solar System.

Most of the nebula condensed to form the Sun but the outer ring did not and revolved around the new star. As the nebula cooled, the cores of the outer four planets started to form as well as many other much smaller cores in the inner Solar System. These smaller cores chaotically collided with each other to form the inner four planets. The inner planets were messy, jagged fragments of collided rock until the gravity they developed pulled these imperfections into a spherical shape.

The remaining pieces of these cosmic rocks had two main fates. One fate was being propelled into the cosmos. Many of these pieces stayed within the orbit of the Sun and formed the spherical Oort Cloud at the edges of our solar system. Some pieces, however, were ejected from our solar system altogether. The other fate was finding a stable orbit around the Sun. One such orbit is located between Mars and Jupiter and is known as the asteroid belt. Another stable orbit is beyond Neptune and is named the Kuiper belt. 

The Planets

There are 8 planets in our solar system: Mercury, Venus, Earth, Mars, Saturn, Jupiter, Uranus, and Neptune. We can classify all planets, including our own, into a few different categories but, for now, we’ll just focus on the inner planets and outer planets of our solar system.

The inner 4 planets are also known as the terrestrial planets. These planets have a heavy-metal core, a solid surface, and are rather dense. Their surfaces can be impacted and shaped by collisions and they have varying levels of atmosphere depending on their size. The inner planets have very few moons in comparison to the outer planets.

The outer planets are somewhat separated into two categories, gas giant and ice giant. The two gas giants are Jupiter and Saturn. They have a low density considering their colossal size and are constructed mostly of their atmosphere. Their cores are theorized to be rocky but, because of the immense pressure that such a massive atmosphere creates, the rock is most likely not in a solid form. Gas giants are composed of the same elements as stars and are sometimes called failed stars because of it. Saturn famously has dazzling bright rings, but Jupiter also has rings, albeit they are faint.

The ice giants are Uranus and Neptune. They have an icy, rocky, core which is much larger than that of the gas giants. The atmosphere of these planets is more elementally complex than the gas giants. These two planets also have rings but, like Jupiter, they are faint. All of the outer planets have dozens of moons.

Another planet you may familiar with is Pluto. Pluto is no longer considered a major planet because it is not able to clear its orbit of celestial objects. There are a few other minor planets in our solar system: Ceres, Haumea, Makemake, and Eris. All of these planets are smaller than Earth’s moon yet have up to 5 moons of their own.

Comets and Asteroids

Comets and asteroids are the leftover bits and pieces from the formation of our planets. Nevertheless, they have differences in composition, orbit, and how they interact with our solar system. The compositions of comets and asteroids have been somewhat unchanged chemically or physically since they first formed. This makes them valuable examples of the chemical structure of the building blocks of our solar system.  

Comets are chunks of frozen gas, rock, and dust. Comets mostly come from the Oort Cloud where there is estimated to be around 10 trillion comets. The Kuiper belt is known for ejecting a comet on occasion. Comets begin their journey around the Sun by being thrown from the Oort Cloud or Kuiper Belt. Comets vary in size and can range from a diameter of a few hundred feet to many miles. When comets come close to the Sun in their elliptical orbit, something spectacular happens. 

The Sun heats up the frozen gas letting it flow to form a vibrant tail that stretches for millions of miles. When a comet comes around the Sun in its orbit, it picks up incredible speed that allows it to slingshot back out into the cosmos. There are around 3,600 known comets flying around in our solar system. Scientists expect many more.

Asteroids are rocky lumps that are vast in quantity and live considerably less spectacular lives than comets. Asteroids primarily reside in the main asteroid belt located between Mars and Jupiter. Over a million asteroids can be found in this belt which spans a width of millions of kilometers. The life of an asteroid becomes a little more interesting when it collides with something. When asteroids collide with Earth, we call them meteorites but most of the time they fail to pass through our atmosphere. An asteroid that burned up before making an impact is called a meteor. 

How Big is Our Solar System?

It is sometimes difficult to comprehend just how big our solar system is. It is important to note that we consider the end of our solar system to be the Oort Cloud, not the last planet in the Sun’s orbit, Neptune. On Earth, we measure large distances in feet, miles, meters, and kilometers. We can try to use these same measuring devices with space, but since space is so vast, we have to make some adjustments to keep the numbers from being burdens to work with. 

The kilometer (km) is approximately the length of 9 football fields. We use kilometers to talk about the diameters of planets or asteroids and comets. In the context of space, the next largest measurement is the astronomical unit (AU). One AU is the distance from the Earth to the Sun, which is about 147.1 million kilometers. We use AUs to talk about the distance between planets in our solar system. After AU comes light-years (LY) which is 63,241.1 AU. A light-year is how far light can travel in one Earth year. We use light-years to talk about how far away objects are in our galaxy. 

To measure the distance from the Sun to the Oort Cloud, we will use astronomical units. Since the Oort Cloud is still relatively unexplored, scientists can only estimate how far it is from the Sun. Right now, we think the distance between the Sun and the Oort Cloud is between 2,000 and 100,000 AU. Let’s do some simple math to find that distance in the aforementioned example of football fields. 

A reasonable 50,000 AU, or 0.79 LY, will be used as our distance for this example. 50,000 AU is a whopping 7,500,000,000,000 kilometers, that’s 7.5 trillion kilometers. We said that 1 kilometer was 9 football fields so that’s an incredible 67,000,000,000,000, or 67 trillion, football fields between the Sun and the Oort cloud. This number is just the radius of our solar system. With this estimate, we can say that our solar system is 134 trillion football fields, or 15 trillion km, from edge to edge. Our solar system is undoubtably enormous.

The post The Ultimate Guide to Our Solar System appeared first on Space Tonight.

Constellations, what are they exactly? The chances are you’ve seen them if you have ever glanced up at the sky. From the “Big Bear” to “Orion”, you may even know about a few of them and the ancient myths that they represent. You may even be wondering why they matter and how you can find them while observing the night sky. In this article, I will shed some light on the constellations and offer some tips that may help you with identifying them.

“The stars we are given. The constellations we make. That is to say, stars exist in the cosmos, but constellations are the imaginary lines we draw between them, the readings we give the sky, the stories we tell.“

Rebecca Solnit

When starting off, one of the first hurdles astronomers must overcome is identifying and knowing most of the constellations. This skill is necessary for navigating the night sky effectively and efficiently. After all, you can’t expect to find something like the Hercules Cluster if you can’t find Hercules.

This may sound incredibly difficult at first, but it is easier than you think! To begin with, I will categorize some of the main constellations into three groups based upon the time of year in which they are visible.

The Northern Circumpolar Constellations

The stars and objects in the night sky behave in the exact same way as the Sun. They rise in the east and set in the west every night due to the Earth’s rotation. This means that some constellations will rise and set depending on both the time of the day and the time of the year we try to observe them at. However, when a constellation is “circumpolar”, it lies within close proximity to the nearest polar star and never sets below the horizon. This means that a circumpolar constellation will always be in the sky no matter the time of day or year. That makes these constellations perfect to learn for beginners!

The number of circumpolar constellations that are visible in the sky depends on your latitude north of the equator; however, there are about five that can be seen almost everywhere in the northern hemisphere. These constellations are Ursa Major the Big Bear, Ursa Minor the Little Bear, Cassiopeia Queen of Ethiopia, Cepheus the King, and Draco the Dragon.

Ursa Major – The Big Bear (The Big Dipper)

Perhaps the most famous circumpolar star arrangements that you can see is the Big Dipper. Contrary to popular belief, the Big Dipper is actually a smaller part of the parent constellation known as Ursa Major the Big Bear. We can find it in the northern sky very easily due to the bright stars that it is made of. There are four bright stars that form its “bowl-like” shape. Two of these stars are known as the “pointer stars” Merak and Dubhe. If an imaginary line is drawn through them, the line will always “point” towards the North Star, Polaris. This trick is extremely useful for finding the Little Dipper. Additionally, other constellations will be easier to find by being able to locate the Big Dipper.

Ursa Minor – The Little Bear (The Little Dipper)

Talking about the Little Dipper, this arrangement of stars is in the constellation of Ursa Minor and contains the north star, Polaris. This star has its reputation because it lines up almost perfectly with the Earth’s axis of rotation. This means that the star will always “appear” to be at the same place in the sky as the Earth rotates. We can see the north star at the end of the Little Dipper’s “handle”. This constellation is a very useful reference point for finding other constellations and for knowing where north is when you are without a compass. Depending on the amount of light pollution around you, it may be hard to make out the entirety of this constellation; however, Polaris will still most likely be visible in any condition.

Cassiopeia – Queen of Ethiopia

As one of the easiest to see circumpolar constellations, Cassiopeia is the constellation directly across the north star from Ursa Major. It is easy to make out in the sky because of it’s “W-like” shape that contains a few relatively bright stars and star clusters Messier 57, Messier 103, and the Owl Cluster (NGC 457).

Cepheus & Draco – The King & The Dragon

Cepheus and Draco are the other two main circumpolar constellations and are relatively dim by comparison to the others. They are both found in the space that surrounds Ursa Minor between Cassiopeia and Ursa Major. Cepheus and Draco may be difficult to see if you have a lot of light pollution in your area.

The Winter Sky

By turning our backs on the northern night sky, we can find a group of constellations that changes depending on the time of the year. We’ll first discuss the ones you can see at the end of the year. These constellations come alive during the winter season due to the Earth’s tilt and location in its orbit around the Sun along with the cleaner and dryer air that winter usually brings. While there are many constellations in the winter sky, the primary ones can be found in a group known as the “Winter Circle” or “Winter Hexagon”.

Orion – The Hunter

Orion the Hunter is perhaps the most famous and easiest to see constellations. He can be identified by his “belt” of three stars in close proximity to each other. It resides at the bottom of the Winter Circle. Betelgeuse and Rigel can be seen at the top left and bottom right of the constellation respectively, and are among the brightest stars in this constellation. Orion’s “sword” is made up of a row of three stars that “hang” down from the belt. Interestingly enough, this middle “star” is actually an object called the Orion Nebula. As we look closer, this object will look more like a fuzzy patch of light than a star.

Canis Major – The Great Dog

If we follow the belt’s direction downwards and to the left, we will find Sirius, the brightest star in the night sky. Sirius is the primary star of Canis Major the Great Dog. Canis Major was one of Orion’s hunting dogs along with Canis Minor. This makes it helpful to remember their placement in the night sky, as they can both be seen “following” Orion from behind.

Taurus – The Bull

Again, we return to the belt of Orion. Now following it upwards and to the right. This will lead us directly to the red star “Aldebaran” and its parent constellation, Taurus the Bull. Taurus contains objects such as the Messier 1 “Crab Nebula” and Messier 45 the “Pleiades” cluster, and is easily identifiable by it’s “V-shape”. The Crab Nebula resides between the “horns” of Taurus. The Pleiades, also known as “the Seven Sisters”, lays up and to the right of the bull (where its shoulder would be).

Auriga – The Charioteer

Auriga the Charioteer is the top constellation of the Winter Circle, residing at the tip of the horns of Taurus. The five stars of this constellation represent a man on a chariot holding a goat in his hand. Of these, there is a primary yellow star that is known as “Capella”. This constellation is just under zenith (the point straight above you in the sky). A useful tip for finding Auriga is to find the tip of Taurus’ “upper horn” because they share the same star.

Gemini – The Twins

If we continue counter-clockwise around the Winter Circle from Auriga, we will come across the two stars “Castor” and “Pollux”. These two stars make up the upper part of Gemini the Twins. Another easy way to find this constellation is to draw a line from Rigel through Betelgeuse in Orion upwards to the relatively rectangular constellation. Gemini, like Taurus, is another Zodiac constellation.

Canis Minor – The Little Dog

Made up of two stars, to complete our journey around the Winter Circle we can find Canis Minor the Little Dog. The main one that resides in the Winter Circle, is the white star “Procyon”. Procyon, Betelgeuse (Orion), and Sirius (Canis Major) make up another pattern called the “Winter Triangle”.

Leo – The Lion

Leo the Lion is outside of the winter circle and to the left of Canis Minor. It looks similar to a backward question mark, with its defining blue star known as “Regulus” on the period. It is another one of the well-known “Zodiac” constellations.

Andromeda / Pegasus

Andromeda and Pegasus are combined by four primary stars known as “The Great Square” and are a rather strange-looking grouping of stars. As a part of the upper section of the constellation, there are two separate branches of stars that are the “legs” of Andromeda. The closest galaxy to our own, the Andromeda Galaxy (Messier 31), is right near these legs. It is rather hard to see in places with a lot of light pollution, but it is definitely a sight to see on a clear night. On the other end of the constellation, there are three strands of stars that all make up the front half of Pegasus.

The Summer Sky

The summer sky is hazier and warmer than the brilliant and clear winter sky. These conditions, along with the tilt and position of the Earth in its orbit, make observing the summer sky a little more difficult. It is also dominated by an arrangement of three stars known as the Summer Triangle. These stars are named “Vega”, “Altair”, and “Deneb”. Each resides in their own respective constellations. Knowing the location of the Summer Triangle makes it a little easier to find some of the other constellations that reside in the summer sky.

Lyra – The Lyre

When searching for Lyra the Lyre, it is the most important to know about its most prominent star, “Vega”. This star is the brightest of the three that make up the Summer Triangle; thus, making it the easiest one to find. It lies near the zenith in the Summer sky. While small, Lyra is useful to know because it is one of the three constellations in the Summer Triangle. This means that knowing its placement can assist us in finding the other constellations.

Cygnus – The Swan

The second constellation in the Summer Triangle is Cygnus the Swan. Perhaps the easiest way to find Cygnus is to first find “Vega” in the constellation of Lyra. Draw a line eastward from Vega to find the prominent star “Deneb”. This star, along with four other prominent stars, forms a shape called the “Northern Cross”. If the amount of light pollution is substantially low, the Northern Cross can be seen immersed in the Milky Way.

Aquila – The Eagle

Find the third prominent star of the summer triangle called “Altair” in order to find Aquila the Eagle. One of the easiest ways to do this is by following the Milky Way downwards until Altair comes into view. Aquila’s appearance is similar to that of a diamond-shaped kite with a tail following behind it. This is the final constellation in the Summer Triangle.

Sagittarius – The Archer

By continuing to follow the Milky Way downwards past Aquila, an arrangement of stars called “the teapot” comes into view. It received its nickname due to the close resemblance it has to the shape of an old-fashioned teapot. The parent constellation to the teapot is in fact, Sagittarius the Archer. Sagittarius acts as our marker for the Center of our Milky Way Galaxy; making the constellation quite significant.

Scorpius – The Scorpion

The red star “Antares” can be found by looking right from the Teapot and staying close to the horizon. The parent constellation to Antares is, in fact, Scorpius the Scorpion. Scorpius is yet another one of the famous Zodiac constellations. Antares is also known as “the Heart” of Scorpius, due to its deep red color.

Boötes – The Herdsman

The final major constellation on this list is known as Boötes the Herdsman. This constellation is to the right, or in the westward direction, from Scorpius. It has a kite-like shape to it, with the red star “Arcturus” at its bottom point. My own high school Astronomy teacher taught me a handy phrase: “arc to Arcturus”. This helps me remember to follow an “arc-like” path from Antares westward to find this constellation. Try this out for yourself!

I hope that you have found this article helpful and informative! Now that I’ve acquainted you with some of the constellations of the night skies, it’s time for you to go hunting for them! Soon you will be able to navigate the sky like the back of your hand, with some time and practice of course.

For Additional Information:

• Charts of the Night Sky – A useful application by Dominic Ford that shows you what your night sky looks like depending upon the time and date. Additionally, this site also allows you to select a plethora of options such as star brightness, the locations of planets, etc.
• Star Atlas – A much more in-depth and interactive application that allows you to explore the night sky.
• Star and Planet Locator – Where you can buy your own Star and Planet Locator, a tool that makes it even easier to navigate the night sky.

The post Constellations: What are they and how to find them? appeared first on Space Tonight.

As one of the most classic scenarios of space science fictions, an asteroid impacting the Earth’s surface could potentially create dramatic changes to those living on our planet. Depending on the size of the asteroid or extraterrestrial object, the resulting impact could be potentially alter the Earth’s current orbit around the sun or create a significant explosion that could level out major cities in a 200-mile (320 km) radius.

By looking at craters on the Earth’s surface, we have evidence that asteroids have impacted the Earth in the planet’s 4.5 billion year history. What are the chances of asteroids hitting the Earth in the near future?

What are the chances of asteroids hitting Earth?

First, it is important understand the importance of Earth’s atmosphere, which is not common to all bodies within our Solar System. Earth’s atmosphere causes a lot of the debris from space to burn up before they hit the Earth’s surface at large sizes.

That’s not to say space debris doesn’t reach the earth’s surface. In fact, that’s far from the truth. Everyday, thousands of tiny debris from space hit the earth — typically the size of a grain of sand or small pebble. So to answer the question about asteroids (defined as any inactive, rocky body orbiting the sun) hitting the earth, the chances are 100% on a daily basis.

On the contrary, if you look at the Moon or Mercury, you can see craters everywhere largely due to their lack of an atmosphere that acts as a buffer between their surfaces and any celestial debris.

Have humans been killed by a meteorite or by the after effects of an impact?

According to NASA, there have been known no humans killed in the past 1,000 years by a meteorite or by a meteorite striking the earth’s surface. There is no record of that happening anywhere on the planet.

However, in Ancient China, there are records of such occurrences. An individual’s chance of getting struck or impacted by a meteorite is very small; however, the risk increases when you deal with regional or global catastrophes that result from objects impacting the surface with a surface area of larger than 1 km².

Predictions on upcoming asteroids entering the Earth’s atmosphere

According to the European Space Agency’s Risk Page, they share a number of objects that have a non-zero probability of impacting the Earth’s surface, with the soonest object expected to fly near-Earth in 2020.

• Object Name: 2018VP1
• Diameter: 2.3 meters
• Date: November 2, 2020
• Link for additional information on 2018VP1

• Object Name: 2009JF1
• Diameter: 13 meters
• Date: May 6, 2022
• Link for additional information on 2009JF1

• Object Name: 2008JL3
• Diameter: 30 meters
• Date: May 1, 2027
• Link for additional information on 2008JL3

• Object Name: 2007KE4
• Diameter: 30 meters
• Date: May 26, 2029
• Link for additional information on 2007KE4

• Object Name: 2012QD8
• Diameter: 90 meters
• Date: March 8, 2047
• Link for additional information on 2012QD8

• Object Name: 99942 Apophis
• Diameter: 375 meters
• Date: April 12, 2068
• Link for additional information on 99942 Apophis

• Object Name: 2000SG344
• Diameter: 30 meters
• Date: September 16, 2071
• Link for additional information on 2000SG344

• Object Name: 2019DS1
• Diameter: 26 meters
• Date: February 26, 2082
• Link for additional information on 2019DS1

• Object Name: 2010RF12
• Diameter: 9 meters
• Date: September 5, 2095
• Link for additional information on 2010RF12

• Object Name: 1979XB
• Diameter: 700 meters
• Date: December 14, 2113
• Link for additional information on 1979XB

How many near-Earth asteroids have been discovered in 2019?

According to NASA, the total number of near-Earth asteroids discovered since the beginning of 2019 was around 19,000. On a given week, NASA expects that 30 new asteroids are discovered, making these near-Earth objects a very common occurrence in the grand scheme of things.

The majority of these space rocks have been found as a result of NASA-funded surveys of the skies, mostly by using ground-based telescopes. In 1998, NASA started to actively catalogue these objects.

Potentially hazardous asteroids (PHA)

The qualification of potentially hazardous asteroids, or PHAs, depend on the size of the asteroids. These asteroids measure at least 460 feet or 140 meters across, which large enough to wipe out an entire US state if they were to hit the earth. At the moment, 8,000 PHAs have been discovered and catalogued.

What can we do about asteroids on the path of collision with Earth?

The field of “asteroid impact avoidance” is associated with a number of methods and approaches that can be deployed to divert the path of an asteroid that is on-track to hitting the Earth’s surface. These “near-Earth objects” are referred by acronym as NEOs.

Generally speaking, the two primary strategies focus on either “destruction” or “diversion.”

Destruction of NEOs

Aptly-named, the destruction of near-Earth objects involve breaking the larger body into harmless fragments that may evaporate as they approach the Earth’s surface. These strategies are typically used against larger objects that may require significant force to re-direct using diversion methods.

• Nuclear explosive devices: Large nuclear explosion set off on or near the asteroid to break up the object.
• Concentrated solar energy: Channeling of solar energy to heat an asteroid and vaporize it. Over the span of long durations, this could provide enough energy to deflect the object.
• Asteroid laser ablation: Similar to concentrated solar energy, a high-powered laser could be used to produce a similar effect.
• Mass driver: A system that would eject material from the asteroid into space, giving steady pushes away from Earth as well as allowing mass to avoid the earth.

Diversion of NEOs

These techniques are responsible for delaying the asteroids path or advancing the asteroids path. Essentially, these are techniques used to ensure that the path of the asteroid does not intersect the path of the earth.

By slowing down the asteroid, we can create asteroid avoidance by allowing the Earth to pass by as our planet is constantly orbiting the sun. In the same way, we could also speed up the asteroid, but this is generally more difficult to accomplish.

• Kinetic impact: Hitting an asteroid with another high-mass object to knock it off course.
• Asteroid tractor: This technique involves adding a small bit of thrust on the asteroid over a long duration to ultimately change its trajectory.
• Ion beam shepherd: Another technique that involves using a low-divergence ion thruster that is pointed at the object from another lighter spacecraft hovering alongside.

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