Our galaxy contains more than just a spiral disk of stars and gas. Like most galaxies there is a large extended halo of material containing stars and dark matter. In the last few years, astronomers have been studying a rarer component in between, wispy hydrogen clouds that lie outside the disk. Now, astronomers have discovered their origin.
H. Alyson Ford led this research as part of her PhD thesis using the Galactic All-Sky Survey taken with the Parkes Telescope in New South Wales, Australia. She, along with Felix J. Lockman of the National Radio Astronomy Observatory and Naomi Mclure-Griffiths of CSIRO Astronomy and Space Science looked at the populations of such clouds in two different regions of the Milky Way.
One such region was right above the tip of the bar of the galaxy. Don't get your hopes up, it's not that kind of bar. A galactic bar is a structure containing stars and gas, similar to a spiral arm, but cutting through the center of the disk. Star formation is much more prevalent here than in the second region studied, and it also had three times as many hydrogen clouds above it, with a higher average height above the plane.
The region of intense star formation creates very massive stars which have strong stellar winds and explode as supernovae at the end of their lives. A series of these going off together creates a "galactic wind" which sends gas out of the plane to later rain down and encourage star formation in another part of the disk. Therefore, these wispy clouds are intimately tied to stellar and galactic evolution.
Though wispy, these clouds contain the mass of hundreds of suns, and hundreds were found in each region studied. They reside 400 to 15,000 light years above the plane of our galaxy which, as Monty Python tells us, "out by us is just 3,000 light years wide." Galactic evolution in general will have to take these into account, and our galaxy is a perfect place in which to study them.
Image Credit: Artist's conception shows Milky Way regions studied, with hydrogen clouds more abundant in region above area where central bar merges with spiral arm. Bright point at bottom center is location of our Solar System. Bill Saxton, NRAO/AUI/NSF
Tags: Astronomy, Dark Matter, Galaxies
comments ( )