Galaxy Study Reveals That The Big Eat the Small To Grow
An extensive study of galaxies reveals that the big ones grow primarily from cannibalizing the smaller ones. Small galaxies, on the other hand, are very efficient at creating new stars from scratch right up until they get gobbled up.
This is just one of the fascinating results of a 7 year study by 90 scientists of a whopping 22,000 galaxies. These scientists were as prolific it seems as the small galaxies they studied since their effort has paid off with 60 publications and 180 more still in the pipeline.
The latest issue of the journal Monthly Notices of the Royal Astronomical Society focuses on just one study though, about how galaxies get bigger. The biggest galaxies of course have deep gravity wells that allow them to suck in all sorts of smaller galaxies, our very own Milky Way has done this in the past. We can tell by examining the unusual tangential motions of a handful of stars in our diffuse halo. These stars are believed to be the remnants of other galaxies that are now orbiting at the outskirts of this halo thousands of light years beyond the edge of the galaxy proper.
In fact, the Milky Way may be balanced at the edge of becoming one of those big galaxies that no longer efficiently collects and condenses gas to create stars. Our primary method of growing now is likely due to eating other smaller galaxies. Why this transition happens is controversial but it is thought that it may be due to the fact that gas in the galaxy is cooked near the nucleus to temperatures too high to later form stars. Small galaxies do not have this problem and therefore have plenty of gas to collect and collapse.
In the far future we will almost certainly consume the nearby dwarf galaxies, the Large and Small Magellanic clouds. This galactic cannibalism cuts both ways however since our nearby and more massive partner galaxy, Andromeda will consume us in 5 billion years to form a new galaxy called the Milkomeda. There’s still plenty of time though to change the address on your business cards.
Image Credit: Simon Driver and Aaron Robotham, ICRAR.