Credit: X-ray: NASA/UMass/D.Wang et al.; Optical: NASA/HST/D.Wang et al.

Hot Galactic Halo

A long-standing controversy regarding our own Milky Way Galaxy is the origin of the diffuse X-ray emission which seems to extend throughout the Galaxy. It's difficult to determine the exact 3-dimensional distribution of this hot X-ray emitting gas since it's difficult to determine the distance to the extended gas. Many astronomers have suggested that some of this hot gas exists in a large halo around the Milky Way, and a new observation with the Chandra X-ray observatory of a spiral galaxy called NGC 4631 helps support this idea. Using Chandra's exquisite resolution, astronomers have seen that some of the X-ray emission from this galaxy originates in a diffuse cloud of hot (2-7 million degree) gas which surrounds the galaxy. The image above show the Chandra observation of the hot gas halo (seen in blue-white in this false color image) superimposed on an image of the galaxy taken by the Hubble Space Telescope. The Hubble image (in orange and white) is dominated by the emission from large groups of stars in the plane of the galaxy, while the X-ray emission seen by Chandra extends far from the galactic plane. It may be that the halo seen by Chandra may be peculiar to NGC 4631, but more observations of other Milky Way-like galaxies will help finally resolve the galactic X-ray halo controversy.

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Page Author: Dr. Michael F. Corcoran
Last modified October 15, 2001