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To Catch a Galactic Thief
Narrator: A big bully of a galaxy has been caught stealing. You might think a galaxy would steal planets or stars or something pretty. But it's actually taking something more valuable – gas.
I'm Whitney Clavin with a podcast from NASA's Jet Propulsion Laboratory.
With us here today to talk about this cosmic caper is Patrick Ogle of the California Institute of Technology. He and this team used a NASA space telescope, called Spitzer, to make their discovery.
Ogle: It's good to be here Whitney.
Narrator: Now, why would a galaxy want to steal gas?
Ogle: The gas is a precious commodity in the sense that it can form new stars. It's basically raw materials, construction materials for a galaxy.
Narrator: So, this galaxy that's stealing the gas – is it making stars out of it?
Ogle: Well, currently the gas is very hot in this particular galaxy. It is so hot that it appears it is not making stars because of that.
Narrator: Will it eventually make stars?
Ogle: It's likely that once the gas cools down to temperatures below 100 degrees or so, it will become cold enough to condense and form new stars. That process will probably take about 10 million stars.
Narrator: Wow. Do you think planets and even life could be forming in this galaxy?
Ogle: Well certainly. We think that planet formation is a natural consequence of star formation. Many planetary systems are being discovered around stars in our own galaxy, so it's very likely that new planets will form once new stars form in this galaxy. We know of at least once example, the Earth, where life has formed on a planet.
Narrator: So, this galaxy is stealing gas. Who is it stealing the gas from?
Ogle: It's stealing the gas from a smaller galaxy that has wandered too close. The galaxy came close enough that it could feel the gravitational forces from the big galaxy very strongly. And the gas gets stripped off of the small galaxy, falling basically downhill toward the massive stars in the big galaxy the same way that water would float downhill here on Earth.
Narrator: So, literally the gas is going down a slope?
Ogle: Correct. It's just like dropping something towards the Earth, rolling down a hill, or rocks falling from space and hitting the Earth. When the gas rolls down into the other galaxy, it heats up to a high temperature because of all the energy it's gained from falling into that galaxy.
Narrator: How hot is the gas?
Ogle: The hottest gas observed with Spitzer is hot enough to melt aluminum here on Earth.
Narrator: Do we have anything that hot on Earth?
Ogle: Yes, in fact, molten lava is hotter than the gas we observed with Spitzer.
Narrator: So, this galaxy is a billion light-years away. Spitzer is actually seeing the gas being stolen?
Ogle: We have an image of the two galaxies, and we can see that stars are actually being stripped from one galaxy and falling toward the other galaxy – something called a tidal tail. So, it's a pathway where material is flowing downhill from one galaxy to the other. So, we can infer that the same thing is happening to gas from the smaller galaxy. And it explains very well why we see this whole large mass of hot gas in the center of the big galaxy.
Narrator: What will happen to the small galaxy, the one that has had all its gas stolen?
Ogle: The small galaxy, once all of its gas is gone, will not be able to form any new stars. Eventually, it will spiral in to the larger galaxy and get gobbled up.
Narrator: Nothing will be left of the small galaxy?
Ogle: They'll have to share all their gas and stars.
Narrator: Are there other scenarios in the universe like this that we know about?
Ogle: Galaxy collisions and mergers are quite common in the universe. And we expect our closest neighbor galaxy, big galaxy, the Andromeda galaxy, to someday collide with our own galaxy hundreds of millions of years from now. It's a very important process for shaping galaxy and determining how they evolve and how many stars they'll form eventually.
Narrator: Are these galaxies like the Milky Way?
Ogle: The big galaxy is about the same mass as the Milky Way. And the smaller galaxy is about half the mass. The reason that we looked at these galaxies is that they have supermassive black holes at the center shooting out relativistic jets of particles. We were interested in studying the black holes. They basically served as a signpost that led us to the energetic phenomenon that we're seeing. And it's likely that the bigger galaxy is stealing gas from the smaller one, and some fraction of that gas is actually falling onto the black hole and generating the jets that we see.
Narrator: And what do you mean by relativistic jets?
Ogle: When matter gets very close to a black hole, it can basically be slingshot at very high speeds away from the black hole, speeds approaching the speed of light. And that's relativistic.
Narrator: But not the speed of light. Is that correct? Nothing can go the speed of light?
Ogle: It can get very close to the speed of light. And, in fact, the jets we see in these galaxies approach 99.999 percent the speed of light. But there is a cosmic speed limit, and that's the speed of light.
Narrator: What if another galaxy got in front of this jet? Would the jet torch the galaxy?
Ogle: That is actually seen in some cases, where the jet runs into another galaxy. And it can have a big impact on the gas that's in the galaxy, that's unfortunate enough to wander by.
Narrator: What excites you the most about this discovery?
Ogle: I think we're seeing a potentially very important stage of galaxy evolution. We've known for a long time that galaxies can merge and come together. But we've never really seen what happens to the gas in them when that happens. Spitzer provides us a new tool for observing this process in detail, and understanding how the gas gets heated up and how it eventually cools off and is able to form new stars out of the remnants of the two original galaxies.
Narrator: It almost sounds like these galaxies are these evolving, blobby creatures.
Ogle: They are very dynamic systems. And they have a life cycle of their own. Gas gets formed into stars. The stars die. They eject the gas back into space, and that gas can start all over again, collect together and form new stars.
Narrator: So, how did you first become interested in astronomy?
Ogle: I actually started out as an amateur astronomer. My father was an amateur astronomer and he had telescopes, and we joined the LA Astronomical society and would go out on weekends and look at galaxies.
Narrator: What were your favorite targets?
Ogle: My favorite thing was to look at the really distant stuff. The faraway galaxies and galaxy clusters. I just thought that was great and amazing that we could see so far. It's very exciting to be able to look toward the edge of the universe and the beginning of time to see how galaxies were formed, and stars and planets and eventually life.
Narrator: Well, thanks for speaking with us.
Ogle: It was my pleasure, Whitney.
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