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HindustanTimes Sun,31 Aug 2014

Life and Universe

Giant gas cloud surrounds Milky Way galaxy
Agencies
September 27, 2012
First Published: 08:19 IST(27/9/2012)
Last Updated: 12:56 IST(27/9/2012)

The Milky Way galaxy is engulfed by a giant cloud of hot gas which extends for hundreds of thousands of light years, Nasa astronomers have found.

The estimated mass of the cloud, also known as a halo, is comparable to the mass of all the stars in the galaxy. According to astronomers, if the size and mass of the cloud is confirmed, it could unravel the "missing baryon" problem for the galaxy. Baryons are particles, such as protons and neutrons, that make up more than 99.9% of the mass of atoms found in the cosmos.

Five astronomers worked with Nasa's powerful space telescope Chandra X-ray Observatory, the European Space Agency's XMM-Newton satellite, and the Japan Aerospace Exploration Agency's Suzaku satellite, to uncover the new study.

Chandra observed eight bright X-ray sources located far beyond the galaxy. The X-rays from these distant sources are absorbed selectively by oxygen ions in the vicinity of the galaxy. According to scientists, 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.

The mass of the halo is estimated to be comparable to the mass of all the stars in the Milky Way galaxy. (Photo courtesy: Nasa)


Other studies have shown that the Milky Way and other galaxies are embedded in warm gas with temperatures between 100,000 and 1 million kelvins. Studies have also indicated the presence of a hotter gas with a temperature greater than 1 million kelvins. According to this new research, the hot gas halo enveloping the Milky Way is much more massive than the warm gas halo.

"We know the gas is around the galaxy, and we know how hot it is," said Anjali Gupta, lead author of The Astrophysical Journal Letters paper describing the research. "The big question is, how large is the halo, and how massive is it?"

"Our work shows that, for reasonable values of parameters and with reasonable assumptions, the Chandra observations imply a huge reservoir of hot gas around the Milky Way," said co-author Smita Mathur of Ohio State University in Columbus. "It may extend for a few hundred thousand light-years around the Milky Way or it may extend farther into the surrounding local group of galaxies. Either way, its mass appears to be very large."

Although there are uncertainties, this new research indicates that the galaxy embedded in gas haloes, such as the one around the Milky Way, may be the hiding spot for many of the missing baryons.

(With inputs from Nasa)


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