BEIJING, Sept. 25 (Xinhuanet) -- Using NASA’s Chandra X-ray Observatory, astronomers have found evidence that the Milky Way galaxy is enveloped by a halo of hot gas extending for hundreds of thousands of light years, according to a paper published in the September issue of the Astrophysical Journal.
The mass of the gas cloud is estimated to be comparable to the mass of all the stars in the galaxy.
"The Chandra observations imply a huge reservoir of hot gas around the Milky Way,” said Smita Mathur, astronomy professor at Ohio State University and co-author of the paper.
A team of five astronomers using data from the Chandra, the European Space Agency’s XMM-Newton space observatory, and Japan’s Suzaku satellite, have determined that the temperature of the absorbing halo is between 1 million and 2.5 million kelvins, or a few hundred times hotter than the surface of the sun.
To answer the question of how large and how massive the halo is, the astronomers supplemented Chandra data on the amount of absorption produced by the oxygen ions with XMM-Newton and Suzaku data on the X-rays emitted by the gas halo.
They were also able to estimate that the mass of the gas is equivalent to the mass in more than 10 billion suns, perhaps as large as 60 billion suns.
The study provides the best evidence yet that the galaxy's missing baryons have been hiding in a halo of million-kelvin gas that envelopes the galaxy, a mystery that has puzzled astronomers for more than a decade.
Baryons are particles, such as protons and neutrons, that make up more than 99.9 percent of the mass of atoms found in the cosmos.