Labeled Image of Galactic Halo
This artist's illustration shows an enormous halo of hot gas (in blue) around the Milky Way galaxy. Also shown, to the lower left of the Milky Way, are the Small and Large Magellanic Clouds, two small neighboring galaxies. The halo of gas is shown with a radius of about 300,000 light years, although it may extend significantly further. Data from NASA's Chandra X-ray Observatory was used to estimate that the mass of the halo is comparable to the mass of all the stars in the Milky Way galaxy. If the size and mass of this gas halo is confirmed, it could be the solution to the "missing-baryon" problem for the Galaxy.
(Credit: NASA/CXC/M.Weiss; NASA/CXC/Ohio State/A Gupta et al;)