Chandra Observatory Shows Milky Way Enveloped in Gas
“The mass of the Milky Way gas envelope is comparable to the combined mass of the rest of the galaxy and, if confirmed, could explain the “missing baryon” problem in physics.”
Astronomers at NASA’s Chandra X-ray Observatory have found evidence that the entire Milky Way Galaxy is surrounded by a sheath of hot gas extending for hundreds of thousands of light years in all directions. The mass of this envelope is comparable to the combined mass of the rest of the galaxy and, if confirmed, could explain the “missing baryon” problem in physics.
Baryons are the sub-atomic particles, comprised of quarks, that make up about 99.9% of the mass of the universe. Notable examples of baryons are protons and neutrons, which in turn are the most common baryons. Electrons are not formed from quarks, and as such are made up of leptons instead of baryons. Observations of extremely distant galaxies and gas halos show that scientists cannot account for about half the baryons observed in those far-off objects in our own time period.
A recent study by five astronomers used information from Chandra, the European Space Agency’s XMM-Newton space observatory, and Japan’s Suzaku satellite to measure the temperature and size of the halo of gas. By measuring the X-rays absorbed by sources located hundreds of millions of light years from the galaxy, they were able to determine that the temperature of the gas surrounding the galaxy clocks in somewhere between 1 and 2.5 million kelvins, several hundred times hotter than the surface of our sun. This is much hotter than earlier measurements of the gas surrounding the galaxy, and this evidence points toward the conclusion that the gas halo is much more massive than previously thought.
“According to these measurements, the mass of the gas could be greater than that of more than 10 billion suns, or could even reach a mass as large as 60 billion suns.”
“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.”
According to these measurements, the mass of the gas could be greater than that of more than 10 billion suns, or could even reach a mass as large as 60 billion suns. This uncertainty depends on certain factors that are not yet measured, such as the amount of oxygen relative to hydrogen, the most common element in the gas cloud. The estimated density of this cloud is very low, however, which is why it had escaped detection until relatively recently.
For more on NASA’s findings on the Milky Way, head over to their website.