02 April 2008

Globular Cluster or Dwarf Galaxy

A few years back when doing research on the mass of dwarf galaxies I asked my advisor what the difference was between a globular cluster and a dwarf galaxy. I was more-or-less scoffed at, as the "obvious" textbook answer is that globulars consist of only old stars and don't have any gas, while galaxies of any sort will have stars of varying ages and will have gas.

New research using Hubble and Gemini South shows the question isn't quite as clear-cut as textbooks like to put it. Our Milky Way galaxy has all these globular clusters orbiting it, but we've also got some dwarf galaxies like the Large and Small Magellenic Clouds. There's this one strange globular cluster, Omega Centauri, which has got multiple generations of stars and a large mass (causing its fast spin), but doesn't seem to have any gas. And now they've discovered that there's an intermediate mass black hole in the center, implying that that Omega Centauri is probably a dwarf galaxy, not a globular cluster after all. Huh, go figure.


Matthew S. Urdan said...

What's really interesting, is in recent months on the science channel, they did a whole series on black holes and their roles in galaxies. It seems that black holes are key to galaxy formation, but they also are a byproduct of the creation of galaxies. As the infant galaxy condenses and spins and the black hole at the center grows more and more massive, eventually there comes a point between event horizon and the speed of the spinning stars and gas surrounding the blackhole that creates a no man's land or neutral zone. Stars outside the neutral zone continue to revolve aroundthe black hole, but don't come close enough to get sucked in. So in between the blackhole at the center of the galaxy and the stars closest to center, is almost a void in space, resulting in a stable galaxy. I thought that was pretty cool.

Good luck on our Battle!

cube said...

The more we know, the more we realize just how little we do know.