Universe Today

What a gorgeous and immense image! And it's full of stars! An astronomer from Central Michigan University has put together a new high-resolution panoramic image of the full night sky , with the Milky Way galaxy as its centerpiece. Axel Mellinger stitched together over 3,000 images to create this beautiful image, which also comes in an interactive version, showing stars 1,000 times fainter than the human eye can see, as well as hundreds of galaxies, star clusters and nebulae.
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Science observations have begun in earnest for the Herschel Space Telescope, and this spectacular image is the first produced by combining data from two cameras aboard Herschel, the Spectral and Photometric Imaging REceiver (SPIRE), and the Photoconductor Array Camera and Spectrometer (PACS). It shows a tumultuous region in the Southern Cross, visible only because the instruments are tuned to "see" in five different infrared wavelengths. Stunning vistas of cold gas clouds lying near the plane of the Milky Way reveal intense, unexpected activity. The dark, cool region is dotted with stellar factories, like pearls on a cosmic string.
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Chandra has done it again in creating some of the most visually stunning images of our Universe. This time, Chandra's X-ray eyes show a dramatic new vista of the center of the Milky Way galaxy. This mosaic from 88 different images exposes new levels of the complexity and intrigue in the Galactic center, providing a look at stellar evolution, from bright young stars to black holes, in a crowded, hostile environment dominated by a central, supermassive black hole.
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Here are some beautiful Milky Way Galaxy pictures. It's important to remember that we live inside the Milky Way Galaxy, so there's no way to show a true photograph of what the Milky Way looks like. We can see pictures of the Milky Way from inside it, or see artist illustrations of what the Milky Way might look like from outside.

This Milky Way Galaxy picture shows what our galaxy would look like from above. You can see its spiral arms, dense core and the thin halo. The Milky Way is a common barred spiral galaxy. There are billions more just like it in the Universe.

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This picture of the Milky Way was captured by NASA's COBE satellite. This photograph was taken using the infrared spectrum, which allows astronomers to peer through the gas and dust that normally obscures the center of the Milky Way.

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This image of the Milky Way Galaxy was taken with the Chandra X-Ray Observatory, which can see in the X-Ray spectrum. In this view, only high energy emissions are visible, such as the radiation emitted from black holes and other high energy objects.

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Here's an artist's impression of what a galaxy like the Milky Way might have looked like early in its history. This image shows a supermassive black hole with young blue stars circling it.

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This is a mosaic image of the Milky Way captured by NASA's Spitzer Space Telescope. It was built up by several photographs taken by Spitzer, which sees in the infrared spectrum, and can peer through obscuring dust.

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For Big Bang advocates, the most updated answer to the question, "How old is the Universe?" is 13.7 billion years, with an uncertainty of only 1%.

Now, this question is not only a thought-provoking one. If you were to direct it to an advocate of cyclical or oscillatory models of the universe, the query wouldn't make sense at all. Hence, when you ask this question, I would have to assume that you are a believer of the one-beginning-one-end version of the cosmological model known as the Big Bang.

Cyclical or oscillatory models, although also offshoots of the Big Bang, are never ending. In these models, you have a sequence of infinite pairs of Big Bangs and Big Crunches (each pair known as a Big Bounce). So, if the Universe expands and collapses into itself infinitely, then there should be no beginning and no end … subsequently, the definition of age cannot be applied here.

You may of course argue that the age you are referring to is specific to a single Big Bang/Big Crunch pair; i.e., the one in which we live in, or how far in time we have gone from the last Big Bang.

So how have scientists arrived at answers to the question "How old is the Universe?"

One method is by finding the oldest globular clusters, a dense bunch of stars having roughly the same age. Basically, once you've determined their age and picked out the oldest, you'd then be able to set a minimum limit to the age of the Universe. For example, if the oldest globular cluster is found to be 10 billion years, then the Universe can't be any younger than that.

This brings us to the next queston: How to spot the oldest globular cluster?

According to astronomers, you should be looking for the dimmest bunch in the sky. That's because the dimmer a star is, the less massive it is. And the less massive it is, the longer it will burn through its supply of hydrogen fuel. Hence, only the oldest stars can burn dimly.

Another method is by determining the current composition of matter and energy density in the Universe then plugging this information into Einstein's theory of General Relativity to compute how fast the Universe has been expanding. This will allow us to retrace its steps back to the point when time was equal zero.

All the necessary information has been gathered with superb accuracy using the Wilkinson Microwave Anisotropy Probe (WMAP) and is the main reason how scientists were able to arrive at 13.7 billion years.

We've got a few articles that touch on how old is the universe here in Universe Today. Here are two of them:

• Age of the Universe
• 13.73 Billion Years – The Most Precise Measurement of the Age of the Universe Yet

NASA also has some more:

• How Old is the Universe?
• Wilkinson Microwave Anisotropy Probe

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• How Old is the Universe?
• The Big Bang and Cosmic Microwave Background

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What is the ultimate fate of our universe? A Big Crunch? A Big Freeze? A Big Rip? or a Big Bounce? Measurements made by WMAP or the Wilkinson Microwave Anisotropy Probe favor a Big Freeze. But until a deeper understanding of dark energy is established, the other three still cannot be totally ignored.

Ever since scientists proved the Big Bang to be the most plausible cosmological theory, and since it only focused more on how it might have all began, their attention started to shift to how the Universe would end. Thus, all 4 theories mentioned above (Big Crunch, Big Freeze, etc.) are actually offshoots of the Big Bang.

The Big Crunch predicts that, after having expanded to its maximum size, the Universe will finally collapse into itself to form the greatest black hole ever.

On the opposite side of the coin, the Big Freeze foretells of a universe that will continue to stretch forever, distributing heat evenly in the process until none is left to be usable enough. Hence, it is also known as the Heat Death.

A more dramatic version of the Big Freeze is the Big Rip. In this scenario, the Universe's rate of expansion will increase substantially so that everything in it, down to the smallest atom, will be ripped apart.

In a cyclic or oscillatory model of the Universe, there will be no end … for matter and energy, that is. But for us and the Universe that we know of, there will definitely be a conclusion. In an oscillatory model, the Big Bang and Big Crunch form a pair known as the Big Bounce. Essentially, such a universe would simply expand and contract (or bounce) forever.

For astronomers to determine what the ultimate fate of the Universe should be, they would need to know certain information. Its density is supposedly one of the most telling.

You see, if its density is found to be less than the critical density, then only a Big Freeze or a Big Rip would be possible. On the other hand, if it is greater than the said critical value, then a Big Crunch or Big Bounce would most likely ensue.

The most accurate measurements on the cosmic microwave background radiation (CMBR), which is also the most persuasive evidence of the Big Bang, shows a universe having a density virtually equal to the critical density. The measurements also exhibit the characteristics of a flat universe. Right now, it looks like all gathered data indicate that a Big Crunch or a Big Bounce is highly unlikely to occur.

To render finality to these findings however, scientists will need to know the exact behavior of dark energy. Is its strength increasing? Is it diminishing? Is it constant? Only by answering these will they know the ultimate fate of the Universe.

We've got a few articles that touch on the fate the universe here in Universe Today. Here are two of them:

• No "Big Rip" in our Future: Chandra Provides Insights Into Dark Energy
• End of the Universe

NASA also has some more:

• The Life and Death of Stars
• What is the Ultimate Fate of the Universe

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• The End of the Universe Part 1: The End of the Solar System
• The End of the Universe Part 2: The End of Everything

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Much of the measurements made that strive to determine the shape of the Universe point to one picture – we are living in a flat universe. This was first declared by a group of scientists working on the Boomerang project and later on confirmed with sharp accuracy by the WMAP (Wilkinson Microwave Anisotropy Probe).

Both the Boomerang experiment and the WMAP draw their conclusions by mapping out cosmic microwave background radiation (CMBR), a faint background glow that is found to be almost the same in all directions. The presence of the CMBR is the most convincing proof that catapulted the Big Bang way ahead of other cosmological theories.

The Big Bang theory has spewed forth theories that strive to predict the way the Universe will end. Among them are the Big Crunch, Big Bounce, Big Freeze, and Big Rip. All four of them are dependent on a handful of factors, and one of them is the Universe's shape.

That the Universe is flat gives us an idea as to how it may meet its ultimate end. The most plausible scenario is a continuous expansion, albeit with an equally continuous decreasing rate. Thus, this shape supports scenarios such as the Big Freeze, and contradicts extreme ones like the Big Rip and exactly opposite ones like the Big Crunch or the Big Bounce.

Unfortunately, a straightforward conclusion cannot be drawn based on this information alone. You see, if the Universe were flat, it would have followed that the average density of matter inside it would have been equal to what is known as the critical density. Alas, it is lesser. In fact, much much less.

A density lesser than the critical value should have only meant one thing: that the Universe is open. Hence, it would contradict other observations that the Universe is flat. To make matters even more complicated, additional information show that the Universe's rate of expansion is accelerating.

To reconcile the differences in gathered data, an entity which was later on called 'dark energy' was introduced. It is believed to be the reason why the expansion is fastest at regions farthest from us. That is to say, the observations that we are getting now can only be possible if dark energy existed in a flat universe.

Before we end, let us clarify that, yes, even in the absence of dark energy, a flat universe will still expand forever. The characteristics of its expansion, however, would be really different. It would not be accelerated.

Flat universe articles are so hot. It's a good thing we've got a nice collection of them here in Universe Today. Here are two of them:

• Further Evidence Found for Dark Energy
• Dark Energy Dominated Universe

Flat universe articles brought to you by Physics World, here are the links:

• The universe is flat – official
• WMAP gives thumbs-up to cosmological model

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• Before the Big Bang
• The Big Bang and Cosmic Microwave Background

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The closed universe model is one of the offshoots of the Big Bang theory. As more proofs supported one theory as to how our universe began (i.e., the Big Bang), scientist's studying cosmology began to shift their attention to a question on the other end of the line – how will our universe end?

Scientists are suggesting 4 possible ways as to how our universe may end: a Big Freeze, a Big Rip, a Big Crunch, or a Big Bounce. Of course, there are other theories but these 4 are the most widely discussed. To predict the Universe's ultimate fate, scientists need to determine a few important factors. The most significant of which are its density and its shape.

Of all the proposed shapes, 3 models stand out: open, closed, and flat.

In terms of the Friedmann equations, a closed universe is obtained when the density parameter, represented by the capital Greek letter Omega (Ω), is greater than unity or Ω > 1. For comparison Ω = 1 denotes a flat universe, while Ω < 1 denotes an open one. Ω is defined as the ratio of the observed density to the critical density. The currently accepted value for the critical density is about 10^-30 grams per cubic centimeter.

The Friedmann equations were introduced by Alexander Friedmann in order to relate all factors that contribute to the expansion of space based on a homogeneous and isotropic model of the Universe and derived out of Einstein's General Relativity.

Notice how both the density and shape of the Universe are supposed to be closely related. For example, a closed universe should be expected for an actual density greater than the critical density. This would subsequently mean that its future will most likely end in either a Big Crunch or Big Bounce.

A closed universe can be imagined to have a positive curvature, much like a sphere. Hence, if somehow you can travel in one direction for a very long time, you can eventually end up in the same position as where you started. Furthermore, if you have two parallel lines on the surface, they will eventually intersect if you trace their paths over large distances, just like the longitude lines in a globe.

The most accurate measurements made in relation to the Big Bang are being gathered through the WMAP (Wilkinson Microwave Anisotropy Probe). The information is based on accurate measurements of the cosmic microwave background (CMB) fluctuations. Interestingly, WMAP measurements are indicative of a flat universe despite the fact that its own density measurements show values lower than the critical density.

This is where the idea of dark energy, which is believed to provide the driving force for the Universe's increasing rate of expansion, comes from.

We've got a few articles that touch on closed universe here in Universe Today. Here are two of them:

• Density of the Universe
• Early Universe's Rapid Expansion Confirmed

NASA also has some more:

• Foundations of Big Bang Cosmology
• Is the Universe Infinite?

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• What is the Shape of the Universe?
• Questions on the Shape, Size and Centre of the Universe

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Where is the center of the Universe? One of the confusing aspects of the whole Big Bang idea is the notion that the Universe doesn't have a center. You see, if we associate the Big Bang with just about any typical explosion, then we can be tempted to pinpoint the source of the explosion to be the center.

For example, if a firecracker explodes and we take a snapshot of it, then the outermost debris would mark the boundaries of the whole explosion. Looking at the directions of each debris, whether outermost or not, would give us an idea as to where the explosion first started and, subsequently, the center.

Furthermore, if there was a point of origin (the center) of the Big Bang similar to typical explosions, then that point and all regions near it would be comparatively warmer than all others. That is, as you move further from the center of a typical explosion, you would expect to measure cooler temperatures.

However, when scientists point their detectors to all directions, the readings they obtain indicate that the Universe, in general, is homogeneous. No large region is relatively warmer than the rest. Of course, each star is hotter than the regions away from it.

But if we look at many galaxies, and thus including the stars that comprise them, a homogeneous overall picture is painted. If that were so, then that center or point of origin of the explosion cannot exist.

The favorite analogy used by lecturers to simplify the concept of a universe having no center is that of the behavior of dots on the surface of an expanding balloon; for as we know, the Universe is expanding. If we imagine the dots to be galaxies, we can visualize the Universe's expansion by observing how the dots are brought away from one another as air is slowly blown into the balloon.

For us to get a near accurate analogy, it is important that the observation be limited to the surface alone. If we try to interpret the expansion as being manifested by the whole balloon, we will be tempted into interpreting the geometric center of the balloon as the center of the expanding Universe.

Going back, if we just focus on the surface, you'll notice that each and every dot will drift farther away from adjacent ones and that no single dot will appear as the center. Also, if you picture yourself as an ant at the center of a single dot, all the other dots will move away from you as if you were the center, just like in our universe.

We've got a few articles that touch on the center of the universe here in Universe Today. Here are two of them:

• More Evidence Earth is Not Center of Universe
• The Earth Goes Around the Sun

NASA also has some more:

• Big Bang theory
• The Big Bang

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• Where is the Centre of the Universe?
• Questions on the Size, Shape and Centre of the Universe

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One of the features of the Big Bang cosmological model is an expanding universe. That is, starting from a very hot and very dense singularity, the components that evolved into what is now our universe first experienced a cataclysmic event. What followed was a continuous expansion, cooling, and thinning out of these components.

The idea that the Universe is expanding has far-reaching ramifications in the field of physics than simply being another amazing astronomical phenomena. For one, it allows for a unification between those who have spent their lives studying the very small and those who have dedicated theirs with the very large.

I am talking about the particle physicists and the astrophysicists. For a long time, particle physicists toiled in the middle of a particle zoo. The discoveries of quarks, leptons, as well as the strong, electromagnetic, weak, and gravitational forces filled their labs with mixed feelings.

On one hand, they were constantly excited with the wealth of discoveries of these numerous tiny particles and their interactions, while on the other, they were conscious of the fact that the diversity of these forces deviated from the idea that nature was biased towards simplicity. They realized these forces should eventually unite for simplicity to prevail.

From their calculations, this was only possible in the presence of very high energies. But since these energies were not present anywhere in the Universe, then the possibility was useless. This puzzle was solved when scientists studying cosmology realized that the Universe was expanding and as a result, was cooling and becoming less dense.

Scientists analyzed that if this were true, then it could be possible that the Universe was once very hot and very dense. In these conditions, the energies would have been very very high. In fact, probably high enough for the 4 forces to unite. It hasn't been proven yet but we're getting there.

Proofs that the Universe experienced a cataclysmic event and, subsequently, that it is expanding are present.

One of them is the detection of the cosmic microwave background radiation exhibiting a thermal black body spectrum of about 3 K. Another is the collection of red shift observations for galaxies, i.e., the further from us the galaxies are, the greater their measured red-shifts. That means, the outermost galaxies are speeding away much faster than the innermost ones. These two alone support the Big Bang theory.

With the construction of the Large Hadron Collider (LHC) at CERN, the conditions that were present during the Big Bang might just be reconstructed. Particle physicists and even astrophysicists are therefore hoping that the anticipated unification of the 4 forces will soon be observed.

We've got a few articles that touch on the expanding universe here in Universe Today. Here are two of them:

• Will the Universe Expand Forever?
• The Universe Is Not Expanding Uniformly

NASA also has some more:

• Hubble Measures the Expanding Universe
• Expanding Universe

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• What is the Universe Expanding Into?
• Before the Big Bang

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One of the most often quoted scientifically-inspired poems is that of Robert Frost's Fire and Ice that begins with, "Some say the world will end in fire;/ Some in ice." These two lines aptly depict two opposing views of how not only the world but the entire universe would end.

There are many theories as to how the end of the Universe would be. Among the more popular ones are Big Freeze or Heat Death, Big Rip, Big Crunch, and Big Bounce.

Two of the theories support an infinite expansion: the Big Freeze and the Big Rip. In the Big Freeze, the Universe is predicted to expand forever, thinning out and cooling down. The Big Rip is a more dramatic version wherein everything will be ripped apart, including atoms.

As with the two previously mentioned theories, the Big Crunch and Big Bounce are closely related. The Big Crunch pertains to the prediction that the Universe, after expanding, will reach a point wherein the forces that pull it together will be enough to overcome the ones that favor expansion.

What will follow is a shrinking, better known as the Big Crunch. The Big Bounce takes this theory a step further. Advocates of the Big Bounce believe that the Big Bang and Big Crunch are actually part of a repetitive sequence of events manifested by an oscillatory universe model.

The success of these two main sets of predictions are largely dependent on the rate of expansion as well as the density of the Universe. Current measurement favor the former; specifically that of the Big Freeze.

The roots of this prevailing theory, also known as the Heat Death, can be traced to the Second Law of Thermodynamics which states that the entropy of an isolated system will always increase. Now, since the Universe is considered as an isolated system, then this prediction should hold true.

What then are the consequences of a system that has reached maximum entropy? This would basically mean that usable energy would cease to exist. It's as if you've wound a clock and it ticks for a certain period of time. However, once it winds down, for as long as nobody is there to wind it back up, it will no longer function.

Thus, essentially, even if our species can somehow survive, say, the expansion of the Sun that might eventually eat up our planet, time will come when the laws of physics will simply not allow our surviving successors to live on in this universe.

We've got a few articles that touch on the end of the universe here in Universe Today. Here are two of them:

• No "Big Rip" in our Future: Chandra Provides Insights Into Dark Energy
• Entropy

NASA also has some more:

• The Life and Death of Stars
• What is the Ultimate Fate of the Universe

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• The End of the Universe Part 1: The End of the Solar System
• The End of the Universe Part 2: The End of Everything

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Knowing the density of the Universe is essential in understanding how the Universe will end. Whether it will go out in a Big Freeze, Big Rip, Big Crunch, or Big Bounce, relies largely on who will win in the biggest tug-of-war ever: that between its momentum of expansion or the pull of gravity. This in turn is largely dependent on its density.

That is, if the density is less than what is known as the critical density, then the expansion will prevail. Otherwise, if the density is greater, then gravity will emerge victorious. The critical density, or the value that separates the two possibilities, is believed to be about 10^-30 grams per cubic centimeter.

Different measurements made on the Universe such as red shifts of the outermost galaxies indicate that not only is the Universe expanding, but its rate of expansion, particularly on the outer rims, is undergoing acceleration. That is, the galaxies that are farthest from us are moving away much faster than those that are nearer.

Density was first thrust into a major role in this grand event when Alexander Friedmann introduced his Friedmann equations, a set of equations that strive to relate all factors that contribute to the expansion of space based on a homogeneous and isotropic model of the Universe. The equations are based on Einstein's General Relativity.

Measurements of the Universe's density, as with all other objects, is easily obtained once its mass and volume is known. Since it would be impossible to measure these physical quantities directly, scientists improvise by sampling a region larger than the scale on which the Universe becomes homogeneous.

To obtain the volume of the selected region, typically taken as a sphere, the radius has to be known. This is calculated based on the maximum redshift at the edge of the said region. The procedure for obtaining the mass is much more sophisticated, making use of an angular size and again the redshift measurements among others.

Based on data gathered by powerful equipment like the WMAP (Wilkinson Microwave Anisotropy Probe), the total density of matter is believed to be equal to the said critical density. If this is true, then the consequence of which is a spatially flat universe. Much of this is also believed to be composed of what they have called as dark energy.

Dark energy, if the scientist's speculations are correct, provides the driving force that can keep the Universe expanding forever.

We've got a few articles here in Universe Today that are related to the density of the Universe. Here are two of them:

• Building a Map of Dark Energy
• A Supernova that Won't Fade Away

NASA also has some more:

• What is the Ultimate Fate of the Universe?
• Foundations of Big Bang Cosmology

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

• Multiple Big Bangs, Satellite Collisions and the Size of the Universe
• Molecules in Space

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Here are ten interesting facts about your home – well, at least your home galaxy – the Milky Way.

1. It's warped.

The Milky Way is a disk about 120,000 light years across (see the Guide to Space article on the diameter of the Milky Way for more), with a central bulge that has a diameter of 12,000 light years. The disk is far from perfectly flat though, as can be seen in the picture below. What warped it? Two of the galaxy's neighbors – the Large and Small Magellanic clouds – have been pulling on the dark matter in the Milky Way like in a game of galactic tug-of-war. The tugging sets up a sort of oscillating frequency that pulls on the hydrogen gas (of which the Milky Way has lots of). Here's a more in-depth article on Universe Today about How the Milky Way got its Warp.

2. It has a halo, but you can't directly see it.

The Milky Way has a halo of dark matter that makes up over 90% of its mass. Yes, 90%. That means that all of what we can see (with the naked eye or telescopes) makes up less than 10% of the mass of the Milky Way. Now, it doesn't have a halo like those old cartoon characters that die, sprout wings and play a harp in the clouds. The halo is actually invisible, though we know it exists by running simulations of what the Milky Way would look like and how fast stars inside the galaxy's disk orbit the center. The heavier it is, the faster they should be orbiting. If you assume that the galaxy is made up only of matter that we can see, then you get a rotation rate for the stars that is well below what it should be, so the rest is made up of what is elusively called "dark matter," or matter that only interacts gravitationally (so far as we know) with "normal matter".

To see some images of the probable dark matter density distribution in our galaxy, check out The Via Lactea Project.

3. It has over 200 billion stars

As galaxies go, the Milky Way is a middleweight. The largest galaxy known, IC 1101, has over 100 trillion stars, and other large galaxies can have more than a trillion stars. Smaller galaxies like the aforementioned Large Magellanic Cloud, have about 10 billion stars. The Milky Way has between 200-400 billion stars, but when you look up into the night sky the most you can see from any one point on the Earth is about 2,500. We aren't stuck with this many stars forever, though, because the Milky Way is constantly losing stars – through supernovae – and producing stars, netting about seven stars per year.

4. It's really dusty and gassy.

You may not think so by looking at it, but the Milky Way is full of dust and gas. And when I say full of dust, I mean that we can only see out about 6,000 light years into the disk of our own galaxy in the visible spectrum, and the galaxy is about 100,000 light years across! The dust and gas makes up a whopping 10-15% of the "normal matter" in the galaxy, with the remainder being stars. The thickness of the dust deflects visible light, as is explained here, but infrared light can pass through the dust, which makes infrared telescopes like the Spitzer Space Telescope extremely valuable tools in mapping and studying the galaxy. Spitzer can peer through the dust to give us extraordinarily clear views of what is going on at the heart of the galaxy and in star-forming regions.

5. It's made up of other galaxies.

The Milky Way wasn't always as it is today, a beautiful barred spiral. It became its current size and shape by eating up other galaxies. It's still doing so today – the Canis Major Dwarf Galaxy is the closest galaxy to the Milky Way because its stars are currently being added to the Milky Way's disk, and our galaxy has consumed others in its long history, such as the Sagittarius Dwarf Galaxy.

6. Every picture you've seen of the Milky Way from above is either another galaxy or an artist's interpretation.

We can't take a picture of the Milky Way from above (yet) because we are inside the galactic disk, about 26,000 light years from the galactic center. This means that any pretty pictures you see of a spiral galaxy with elegant arms that is supposedly the Milky Way is either a picture of another spiral galaxy, or the rendering of a talented artist. Imaging the Milky Way from above is a long, long way off; however, this doesn't mean that we can't take breathtaking images of the Milky Way from our vantage point!

7. There is a black hole at the center.

Most galaxies have a supermassive black hole at the center. Ours is no exception. The center of our galaxy is called Sagittarius A* (pronounced "A-star"), and it houses a black hole with a mass of 40,000 Suns that is 14 million miles across (about the size of Mercury's orbit). But this is just the black hole itself. All of the mass trying to get into the black hole – called the accretion disk – forms a disk that has a mass of 4 million Suns, and would fit inside the orbit of the Earth. Though like other black holes, Sgr A* tries to consume anything that happens to be nearby, star formation has been detected near this black hole behemoth.

8. It's almost as old as the Universe itself.

The most current estimate for the age of the Universe is about 13.7 billion years. Our Milky Way has been around for about 13.6 billion of those years, give or take 800 million years. The oldest stars in our the Milky Way are found in globular clusters, and the age of the galaxy is determined by taking the age of these stars, and then extrapolating the age of what preceded them. Though some of the constituents of the Milky Way have been around for a long time, the disk and bulge themselves didn't form until about 10-12 billion years ago, and the bulge may have formed earlier than the rest of the galaxy.

9. It's part of the Virgo Supercluster, a grouping of galaxies within 150 million light years.

As big as it is, the Milky Way is part of an even bigger structure called a supercluster. Superclusters are groupings of galaxies on very large scales (100s of millions of light years). In between these superclusters are large voids of space where any space traveler would encounter very little in the way of galaxies or matter. Our close neighbors include the Large and Small Magellanic Clouds, and the Andromeda Galaxy (the closest spiral galaxy to the Milky Way), and along with about 30 other galaxies this group of galaxies makes up what is called the Local Group. But as you get further on out, on the scale of hundreds of millions of light years, the Milky Way can be seen to be just a small part of a large grouping of galaxies 150 million light years in diameter called the Virgo Supercluster.

10. It's on the move

The Milky Way, along with everything else, is moving through space, and puts to shame anything from everyday life that one could compare its speed to. The Earth moves around the Sun, the Sun around the Milky Way, and the Milky Way is part of the Local Group, which is moving relative to the Cosmic Microwave Background radiation – the radiation left over from the Big Bang, which is a convenient reference point to use when determining the velocity of things in the Universe. The Local Group is calculated to move relative to the CMB at about 600 km/s (2,200,000 km/h), which is pretty darn fast!

For many more facts about the Milky Way, visit the Guide to Space, listen to the Astronomy Cast episode on the Milky Way, or visit the Students for the Exploration and Development of Space at seds.org.

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Our Milky Way's black hole is quiet – too quiet – some astronomers might say. But according to a team of Japanese astronomers, the supermassive black hole at the heart of our galaxy might be just as active as those in other galaxies, it's just taking a little break. Their evidence? The echoes from a massive outburst that occurred 300 years ago.
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