Multimedia Gallery
Milky Way Hydrogen Clouds
Artist's conception showing regions of the Milky Way studied by researchers, with hydrogen clouds more abundant in the region above the area where the central bar merges with the spiral arm; bright point at bottom center is location of our solar system.
The discovery of gas clouds in and above the Milky Way that have preferred locations has given astronomers a key clue about the origin of such clouds, which play an important part in galaxy evolution.
More about this Image
The discovery of these abundant hydrogen gas clouds was made by H. Alyson Ford of the University of Michigan, whose Ph.D. thesis research from Swinburne University formed the basis for this work. Ford worked in collaboration with Felix Lockman of the National Radio Astronomy Observatory (NRAO) and Naomi Mclure-Griffiths of Commonwealth Scientific and Industrial Research Organisation (CSIRO) astronomy and space science.
"We've concluded that these clouds are gas that has been blown away from the galaxy's plane by supernova explosions and the fierce winds from young stars in areas of intense star formation," said Ford.
Ford and the team studied gas clouds in two distinct regions of the Milky Way and located between 400 and 15,000 light years outside the disk-like plane of the galaxy. The disk contains most of the galaxy's stars and gas, and is surrounded by a halo of gas more distant than the clouds the astronomers studied.
First detected with the National Science Foundation's Robert C. Byrd Green Bank Telescope, the clouds are in a transitional area between the disk and the halo, and their origin has been uncertain. The research team used data from the Galactic All-Sky Survey, made with CSIRO's Parkes Radio Telescope in Australia.
When comparing the observations of the two regions, the astronomers saw that one region contained three times as many hydrogen clouds as the other. In addition, that region's clouds are, on average, twice as far above the galaxy's plane. The astronomers believe this difference is due to the fact that the region with more clouds lies near the tip of the galaxy's central "bar," where the bar merges with a major spiral arm. This is an area of intense star formation, containing many young stars whose strong winds can propel gas away from the region. The most massive stars also will explode as supernovae, blasting material outward. In the other region they studied, star formation activity is more sparse.
The clouds consist of neutral hydrogen gas, with an average mass equal to that of about 700 suns. Their sizes vary greatly, but most are about 200 light years across. The astronomers studied about 650 such clouds in the two, widely separated regions of the galaxy. (Date of Image: 2010)
SORRY: THIS IMAGE IS NOT AVAILABLE IN HIGH RESOLUTION FORMAT
Credit: Bill Saxton, NRAO/AUI/NSF
Images and other media in the National Science Foundation Multimedia Gallery are available for use in print and electronic material by NSF employees, members of the media, university staff, teachers and the general public. All media in the gallery are intended for personal, educational and nonprofit/non-commercial use only.
Images credited to the National Science Foundation, a federal agency, are in the public domain. The images were created by employees of the United States Government as part of their official duties or prepared by contractors as "works for hire" for NSF. You may freely use NSF-credited images and, at your discretion, credit NSF with a "Courtesy: National Science Foundation" notation.
Additional information about general usage can be found in Conditions.
Also Available:
Download the high-resolution JPG version of the image. (419 KB)
Use your mouse to right-click (Mac users may need to Ctrl-click) the link above and choose the option that will save the file or target to your computer.