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I get this question... a lot.

"Since astronomers know that the Universe is expanding, what's it expanding into? What's outside of the Universe?"

The short answer is that this is a nonsense question, the Universe isn't expanding into anything, it's just expanding.

The definition of the Universe is that it contains everything.

If something was outside the Universe, it would also be part of the Universe too.

Outside of that? Still Universe. Out side of THAT? Also more Universe. It's Universe all the way down.

But I know you're going to find that answer unsatisfying, so now I'm going to break your brain.

Either the Universe is infinite, going on forever, or its finite, with a limited volume.

In either case, the Universe has no edge.

When we imagine the Universe expanding after the Big Bang, we imagine an explosion, with a spray of matter coming from a single point. But this analogy isn't accurate.

A better analogy is the surface of an expanding balloon. Not the 3 dimensional balloon, just its 2 dimensional surface.

If you were an ant crawling around the surface of a huge balloon, and the balloon was your whole universe, you would see the balloon as essentially flat under your feet.

Imagine the balloon is inflating. In every direction you look, other ants are moving away from you. The further they are, the faster away they're moving.

Even though it feels like a flat surface, walk in any direction long enough and you'd return to your starting point.

You might imagine a growing circle and wonder what it's expanding into. But that's a nonsense question. There's no direction you could crawl that would get you outside the surface. Your 2-dimensional ant brain can't comprehend an expanding 3-dimensional object.

There may be a centre to the balloon, but there's no center to the surface. Just a shape that extends in all directions and wraps in upon itself.

And yet, your journey to make one lap around the balloon takes longer and longer as the balloon gets more inflated.

To better understand how this relates to our Universe, we need to scale things up by one dimension, from a 2-d surface embedded in a 3-d world, to a 3-d volume embedded within a 4-d universe.

Astronomers think that if you travel in any direction far enough, you'll return to your starting position. If you could stare far enough into space, you would be looking at the back of your own head.

And so, as the Universe expands, it would take you longer and longer to lap the Universe and return to your starting position.

But there's no direction you could travel in that would take you outside or "off" of the Universe.

Even if you could move faster than the speed of light, you'd just return to your starting position more quickly.

We see other galaxies moving away from us in all directions just as our ant would see other ants moving away on the surface of the balloon.

A great analogy comes from my Astronomy Cast co-host, Dr. Pamela Gay.

Instead of an explosion, imagine the expanding Universe is like a loaf of raisin bread rising in the oven.

From the perspective of any raisin, all the other raisins are moving away in all directions.

But unlike a loaf of raisin bread, you could travel in any one direction within the bread and eventually return to your starting raisin.

Remember that our entire comprehension is based on 3-dimensions. If we were 4-dimensional creatures, this would make much more sense.

For a much deeper explanation, I highly recommend you watch my good friend, Zogg the Alien explain how the Universe has no edge.

After watching his videos, you should totally understand the possible topologies of our Universe.

I hope this helps you understand why there's no answer to "what is the Universe expanding into?"

With no edge, it's not expanding into anything, it's just expanding.

Host: Fraser Cain
Guests: David Dickinson, Amy Shira Teitel, Jason Major, Nicole Gugliucci

David:
The Geminid meteors
China landing on the Moon
Space Station Coolant Issues

Fraser:
The Year in Space Calendar Giveaway on Universe Today
Kerbal Space Program game on sale on Steam TODAY!
UT's Phases of the Moon App on iOS is FREE Monday, 12/16/2013

Jason:
Jets on Europa
Star not a star
Lakes on Titan

Amy:
Exoplanet with the biggest orbit

Nicole:
New Cosmoquest Android App -- Earth or not Earth?
Molecular cloud M51

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page.

Read more: http://www.universetoday.com/107162/w...

We owe our entire existence to the Sun.

Well, it and the other stars that came before.

As they died, they donated the heavier elements we need for life.

But how did they form?

Stars begin as vast clouds of cold molecular hydrogen and helium left over from the Big Bang.

These vast clouds can be hundreds of light years across and contain the raw material for thousands or even millions of times the mass of our Sun.

In addition to the hydrogen, these clouds are seeded with heavier elements from the stars that lived and died long ago.

They're held in balance between their inward force of gravity and the outward pressure of the molecules.

Eventually some kick overcomes this balance and causes the cloud to begin collapsing.

That kick could come from a nearby supernova explosion, collision with another gas cloud, or the pressure wave of a galaxy's spiral arms passing through the region.

As this cloud collapses, it breaks into smaller and smaller clumps, until there are knots with roughly the mass of a star.

As these regions heat up, they prevent further material from falling inward.

At the center of these clumps, the material begins to increase in heat and density.

When the outward pressure balances against the force of gravity pulling it in, a protostar is formed.

What happens next depends on the amount of material.

Some objects don't accumulate enough mass for stellar ignition and become brown dwarfs - substellar objects not unlike a really big Jupiter, which slowly cool down over billions of years.

If a star has enough material, it can generate enough pressure and temperature at its core to begin deuterium fusion - a heavier isotope of hydrogen.

This slows the collapse and prepares the star to enter the true main sequence phase.

This is the stage that our own Sun is in, and begins when hydrogen fusion begins.

If a protostar contains the mass of our Sun, or less, it undergoes a proton-proton chain reaction to convert hydrogen to helium.

But if the star has about 1.3 times the mass of the Sun, it undergoes a carbon-nitrogen-oxygen cycle to convert hydrogen to helium.

How long this newly formed star will last depends on its mass and how quickly it consumes hydrogen.

Small red dwarf stars can last hundreds of billions of years, while large supergiants can consume their hydrogen within a few million years and detonate as supernovae.

But how do stars explode and seed their elements around the Universe? That's another episode.

We recently interviewed Dr. Kevin Grazier, on of the scientist who has worked extensively on the Cassini mission. Here's what he had to tell us about that mission's discoveries.
"My name is Kevin Grazier. I am a planetary scientist, and for my research I do long-term integrations or simulations of early solar system evolution. I'm a former scientist on the Cassini mission and a consultant to several TV series such as Defiance, Falling Skies, the movie Gravity, and formerly, Battlestar Galactica."
What are Cassini's most amazing discoveries?
"Cassini has essentially rewritten the book on the Saturn system. I was on the spacecraft team for 15 years. I worked as a science planner and as the Investigation Scientist on the ISS instrument. (That's Imaging Science Subsystem, not International Space Station.) And of the discoveries we found, I'm trying to think of what I'd call or classify as the most exciting."
"One was predicted -- the fact that it was believed that there could be ice volcanoes on Enceladus. And as a matter of fact, there are volcanoes on Enceladus, or active venting, however you want to look at that. Those vents create the "E" ring, so we have a ring created by material vented off Enceladus. That's pretty exciting, because we see an active object venting material, and there aren't a lot of active objects in the solar system."
"The surface of Titan is really fantastic. We have open oceans or seas of hydrcarbons on Titan. We have the possibility of an open ocean underneath the crust, just like we believe is under the surface of Europa."
"We have one image which seems to capture what might be a volcanic eruption. That's important, because in the outer solar system, planetary science considers ice a rock. What a rock is defined as depends on where you are in the solar system. So in the outer solar system, ice is a rock. All of the moons in the outer solar system except Io have icy crusts. Now, if you have a volcanic eruption on Titan, we have an eruption of magma, and if ice is a rock, that eruption is water. So we have evidence of magma chambers which could be cauldrons of life-giving water."
"How cool is that? How counter-intuitive is that? How science-fiction-y is that? That one of the most interesting places to look for is a lava chamber or magma chamber that could be suitable for sustaining life. I think that's really exciting."
You can follow Dr. Kevin on Twitter here: https://twitter.com/kevingrazier

Read more: http://www.universetoday.com/?p=10799...

The Universe is expanding. Distant galaxies are moving away from us in all directions.

It's natural to wonder, is everything expanding?

Is the Milky Way expanding?

What about the Solar System, or even objects here on Earth. Are atoms expanding?

Nope.

The only thing expanding is space itself.

Imagine the Universe as loaf of raisin bread rising in the oven.

As the bread bakes, it's stretching in all directions - that's space.

But the raisins aren't growing, they're just getting carried away from each other as there's more bread expanding between them.

Space is expanding from the Big Bang and the acceleration of dark energy.

But the objects embedded in space, like planets, stars, and galaxies stay exactly the same size.

As space expands, it carries galaxies away from each other.

From our perspective, we see galaxies moving away in every direction.

The further galaxies are, the faster they're moving.

There are a few exceptions.

The Andromeda Galaxy is actually moving towards the Milky Way, and will collide with us in about 4 billion years.

In this case, the pull of gravity between the Milky Way and Andromeda is so strong that it overcomes the expansion of the Universe on a local level.

Within the Milky Way, gravity holds the stars together, and same with the Solar System.

The nuclear force holding atoms together is stronger than this expansion at a local scale.

Is this the way it will always be?

Maybe. Maybe not.

A few decades ago, astronomers thought that the Universe was expanding because of momentum left over from the Big Bang.

But with the discovery of dark energy in 1998, astronomers realized there was a new possibility for the future of the Universe.

Perhaps this accelerating dark energy might be increasing over time.

In billions years from now, the expansive force might overcome the gravity that holds galaxies together.

Eventually it would become so strong that star systems, planets and eventually matter itself could get torn apart.

This is a future for the Universe known as the Big Rip.

And if it's true, then the space between stars, planets and even atoms will expand in the far future.

Is this going to happen?

Astronomers don't know.

Their best observations so far can't rule it out, or confirm it.

And so, future observations and space missions will try to calculate the rate of dark energy's expansion.

So no, matter on a local level isn't expanding.

The spaces between planets and stars isn't growing.

Only the distances between galaxies which aren't gravitationally bound to each other is increasing.

Because space itself is expanding.

Imagine a really bad day. Perhaps you're imagining a day where the Sun crashes into another star, destroying most of the Solar System.

No? Well then, even in your imagination things aren't so bad... It's all just matter of perspective. Fortunately for us, we live in out the boring suburbs of the Milky Way. Out here, distances between stars are so vast that collisions are incredibly rare.

There are places in the Milky Way where stars are crowded more densely, like globular clusters, and we get to see the aftermath of these collisions. These clusters are ancient spherical structures that can contain hundreds of thousands of stars, all of which formed together, shortly after the Big Bang.

Within one of these clusters, stars average about a light year apart, and at their core, they can get as close to one another as the radius of our Solar System.

With all these stars buzzing around for billions of years, you can imagine they've gotten up to some serious mischief. Within globular clusters there are these mysterious blue straggler stars. They're large hot stars, and if they had formed with the rest of the cluster, they would have detonated as supernovae billions of years ago.

So scientists figure that they must have formed recently. How?

"Hi, I'm Professor Mark Morris of the University of California at Los Angeles in the Department of Physics and Astronomy."

Astronomers think they're the result of a stellar collision. Perhaps a binary pair of stars merged, or maybe two stars smashed into one another.

"When you see two stars colliding with each other, it depends on how fast they're moving. If they're moving at speeds like we see at the center of our galaxy, then the collision is extremely violent. If it's a head-on collision, the stars get completely splashed to the far corners of the galaxy. If they're merging at slower velocities than we see at our neck of the woods in our galaxy, then stars are more happy to merge with us and coalesce into one single, more massive object."

There's another place in the Milky Way where you've got a dense collection of stars, racing around at breakneck speeds... near the supermassive black hole at the center of the galaxy. This monster black hole contains the mass of 4 million times the Sun, and dominates the region around the center of the Milky Way.
Stars whip around it, like comets dart around our Sun, and interactions are commonplace.
There's another scenario that can crash stars together. The Milky Way mostly has multiple star systems. Several stars can be orbiting a common center of gravity. Many are great distances, but some can have orbits tighter than the planets around our Sun.

When one star reaches the end of its life, expanding into a red giant, It can consume its binary partner. The consumed star then strips away 90% of the mass of the red giant, leaving behind a rapidly pulsating remnant.

What about when galaxies collide? That sounds like a recipe for mayhem.
Surprisingly, not so much.

Read more at http://www.universetoday.com/107244/c...
Thanks to Professor Mark Morris at UCLA - visit the Physics and Astronomy program homepage at http://www.pa.ucla.edu/.