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In the beginning was the Big Bang. From that came everything - galaxies, stars, planets, you and me. But how did it all happen?

Dr Graham Phillips
Wouldn't it be wonderful if you could just kick back and watch a movie of the life of the universe and actually see how everything unfolded? Well, thanks to a new scientifically accurate computer simulation, you kind of can.

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This is the Illustris program - the most advanced computer model of the universe. On a supercomputer, it took three months to run. That's equivalent to more than 2,000 years on your home computer. It was created by a large international team of astrophysicists. One of them was Boston's Paul Torrey.

Dr Paul Torrey
The Illustris simulation is our attempt to simulate a slice of the universe from soon after the Big Bang until the present day.

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The program's made its mark around the world including here in Melbourne.

Dr Graham Phillips
How impressive is this simulation?

Dr Alan Duffy
I think, as you can see, it's incredibly impressive, and seeing really is believing.

Dr Michael Brown
The Illustris simulation is really getting a lot of detail there that wasn't present in previous simulations.

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And it not only gets the detail - it models a huge chunk of the universe, a cube 350 million light-years across that encompasses tens of thousands of galaxies. To appreciate why the simulation is so good, you first need to know a little about our universe's majestic inhabitants - galaxies. They're so beautiful, I put one on the lounge wall.

Dr Graham Phillips
This is the Sombrero Galaxy. Stunning, isn't it? But imagine it as an Impressionist painting made up of billions of little dots. Now, each one of those dots is a star.

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There are about 100 billion stars in a typical galaxy and there are many billions of galaxies in the observable universe.

Dr Graham Phillips
Space is really, really big.

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Our star, the sun, is in the Milky Way.

Dr Paul Torrey
The Milky Way is a spiral galaxy that actually is a fairly common galaxy within the local universe. We think that about 70% of local galaxies are star-forming discs that have spiral arms of some sort.

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Star-forming is one of the key jobs of a spiral galaxy. It's currently happening in our Orion Nebula. This is an enlarged image of it taken by the Hubble Telescope.

Dr Graham Phillips
It's a pretty amazing facility.

Dr Michael Brown
It is. You get to walk inside the Orion Nebula and see it in Hubble detail.

Dr Graham Phillips
I can see a little black smudge over there. What's that?

Dr Michael Brown
So, that black splodge is a solar system being born. A new star being formed and a disk of dust and gas that's gonna collapse and form planets.

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While our galaxy is a spiral, the other major type is elliptical.

Dr Michael Brown
Elliptical galaxies are the largest galaxies in the universe. These galaxies are sort of football-shaped or soccer ball-shaped, and they don't really have much star formation within them.

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So why do galaxies come in these two very different varieties? To find out brings us back to the Illustris simulation. It begins just a few tens of millions of years after the Big Bang. There were no stars or galaxies then, just a universe filled with gas made of ordinary matter, and dark matter.

Dr Alan Duffy
Dark matter is invisible, it doesn't interact with light, so we can't see it.

Dr Michael Brown
There's lots of it, it holds galaxies together, but exactly what it is, what kind of particle it is, still remains a mystery.

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But it does have gravity. In the early universe, Illustris depicts dark matter as blue, and gravity causes it to gradually clump together, forming a vast scaffold for the ordinary-matter galaxies to form around. It's in the high-density spots the first galaxies appear. Zoom into one and you see why Illustris is so impressive. Incredible detail has been modelled and realistic-looking galaxies have been produced.

Dr Paul Torrey
Here we're zooming in on one galaxy which actually happens to have a lot of properties similar to our own Milky Way galaxy. We see that is has blue star-forming arms and that it has an overall disc-like structure.

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And remarkably, Illustris also produces the other kind of galaxies, the ellipticals.

Dr Paul Torrey
I think the most novel aspect of the simulation is the formation of both disk-like systems and elliptical systems side by side. That had been really hard to do in the past.

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Elliptical galaxies form from spirals.

Dr Alan Duffy
This is when two massive galaxies collide together and they just essentially cause a train wreck, a gravitational train wreck where all of the nice structure of spirals, everything like that, is just obliterated and we find this slightly elongated structure forming essentially an elliptical blob of light on the sky, hence the name.

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And to make things personal, racing towards to us right now is the spiral Andromeda Galaxy. It's travelling at 120km per second.

Dr Alan Duffy
It really is a Jaws moment. It's gonna take a few billion years, but there's a bit of a collision coming.

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When Andromeda collides with us, it could look a bit like this.

Dr Paul Torrey
What happens is that two galaxies first come close to one another, they go by for one first passage and that's a very strong interaction that they have there.

Dr Alan Duffy
Gonna swing back towards each other and slosh around a little bit.

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Remarkably, while the galaxy's structure changes completely none of the billions of the stars in either galaxy is likely to hit another, because there's so much space between the stars.

Dr Michael Brown
So when the two galaxies collide, the stars will actually pass by each other and there will be very few collisions between the stars.

Dr Paul Torrey
It's unlikely that the sun or even the Earth will be disturbed by this merger. Eventually, the stars come together and mix in such a way that in fact we can't distinguish the two galaxies from one another.

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At that point, our spiral Milky Way will have become an elliptical. To see another example of Illustris's realism wind time forward to about five billion years after the Big bang. These bubbles are enormous outpourings of energy that spread matter from galaxy to galaxy. They come from supermassive black holes.

Dr Michael Brown
Almost every large galaxy has a supermassive black hole. Our galaxy has a black hole that weighs millions of times the mass of the sun, and there's black holes out there that way a billion times the mass of our own sun.

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When some unsuspecting matter falls into one of these black holes, huge jets of energy shoot out. Illustris actually allows us to visualise these gigantic bubbles spreading through the cosmos.

Dr Graham Phillips
Now, while the realistic details Illustris produces are pretty impressive, perhaps the most convincing demonstration of its realism is a single picture.

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The Hubble Space Telescope took this picture of deep space several years ago. Those tiny splodges are entire galaxies.

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Paul's team put a mock Hubble in their simulation and took a virtual picture in their virtual universe.

Dr Paul Torrey
We gave our mock Hubble Space Telescope the same camera, the same lens size and the same filters, so that the image should be really analogous to what's actually seen in the real Hubble Space Telescope image.

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On the left is the real Hubble image. On the right is the one from the mock Hubble. The two were extraordinarily similar. Illustris shows we do now understand the basics of our universe evolved. If you'd like to look at the full Illustris simulation, go to our website.

STORY CONTACTS

Dr Paul Torrey 
Astrophysicist
Massachusetts Institute of Technology

Dr Michael Brown 
Astrophysicist
Monash University

Dr Alan Duffy 
Astrophyscist
Swinburne University of Technology
Melbourne