io9: when galaxies collide

Andromeda Surrounded By The Remains Of The Dwarf Galaxies It's Killed

Charlie Jane Anders — Thu, 03 Sep 2009 14:30:00 PDT

Our neighboring Andromeda Galaxy may look benign, but it's really a massive cannibal, sitting surrounded by the undigested remnants of the galaxies it's eaten. European scientists have mapped the galaxy anew, and found stars that came from elsewhere.

Writing in the new issue of Nature, the researchers explain that Andromeda is surrounded by a halo of remnants from other galaxies, and this provides evidence for the "hierarchical" model of galaxy development, where bigger galaxies grow by eating smaller ones:

In hierarchical cosmological models1, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound stars surrounding the galaxy, at distances that reach 10–100 times the radius of the central disk2, 3. The number, luminosity and morphology of the relics of this process provide significant clues to galaxy formation history4, but obtaining a comprehensive survey of these components is difficult because of their intrinsic faintness and vast extent. Here we report a panoramic survey of the Andromeda galaxy (M31). We detect stars and coherent structures that are almost certainly remnants of dwarf galaxies destroyed by the tidal field of M31. An improved census of their surviving counterparts implies that three-quarters of M31's satellites brighter than Mv = -6 await discovery. The brightest companion, Triangulum (M33), is surrounded by a stellar structure that provides persuasive evidence for a recent encounter with M31. This panorama of galaxy structure directly confirms the basic tenets of the hierarchical galaxy formation model and reveals the shared history of M31 and M33 in the unceasing build-up of galaxies.

And here's a cool looking picture of Andromeda's orbit that they released:

Image of Triangulum Galaxy from NASA.

One Galaxy Smashes Into Four Others At 2 Million Miles Per Hour

Charlie Jane Anders — Tue, 14 Jul 2009 10:09:33 PDT

Stephan's Quintet sounds like the name of a nice jazz group, but this galactic cluster, discovered 250 years ago, is actually one galaxy passing through four others at nearly 2 million miles per hour. Hence the long tails. [Chandra Observatory]

When Galaxies Collide! And Then Eat Each Other!

grae — Wed, 09 Jan 2008 07:00:45 PST

There are moments when I think that science exists purely to blow my puny human mind. Take galaxy NGC 4622, for example. For years now, astronomers have wondered about the fact that it seemed to be moving in reverse, spinning towards the direction of its spiral arms instead of away from them. Now a new analysis of images of NGC 4622 has revealed that there's more to the galaxy than thought. Namely, it may be deformed because it swallowed another galaxy.

I'll say that again, in case you missed it: Scientists have found a galaxy that might have swallowed another galaxy. The further analysis of images of NGC 4622, you see, revealed that the galaxy actually has another set of arms inside the center, arms that trail in the opposite direction to the known arms. According to New Scientist, that got them thinking:

Scientists still do not understand how the galaxy got its oppositely oriented arms. One possibility is that the inner arms are the result of a struggle with a smaller galaxy that veered perilously close to NGC 4622 and was swallowed. Before being ripped to shreds, the smaller galaxy could have stirred up matter in NGC 4622's inner regions, leading it to settle in a spiral pattern opposite to that in the outer regions.

It's as if the universe saw the last Fantastic Four movie, got upset at their take on Galactus and decided that it could come up with something much more impressive and with a bigger appetite. Of course, this now makes me more optimistic at our odds of finding a real-life Silver Surfer, so it's not all bad news.

Image courtesy NASA

Galaxy's spiral arms point in opposite directions [New Scientist]