Astronomers have discovered a cloud of gas surrounding the Milky Way galaxy, which weighs as much as all of the stars inside it.
The cloud that surrounds our galaxy is also called a halo, and it appears to be enormous as it extends hundreds of thousands of light years across, reports Space.com.
Scientists believe it is mainly made up of hydrogen along with some oxygen and other elements. NASA’s Chandra X-ray Observatory, the European Space Agency’s XMM-Newton space observatory, and Japan’s Suzaku satellite were all used to measure the halo’s temperature, size, and mass.
Researchers believe the mass inside the galaxy’s halo may be the answer to the “missing baryon problem.” Baryons are a class of subatomic particles, which include protons and neutrons. They make up the atoms present inside stars and galaxies.
Theories about the formation and evolution of the universe predict that there should be more baryons than we see. While only half of the baryons predicted have been accounted for, the gas halo could be the hiding spot for the other half. NASA officials wrote about the find:
“Although there are uncertainties, the work by Gupta (Anjali Gupta, lead author of a paper reporting the findings in The Astrophysical Journal) and colleagues 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.”
Business Insider notes that previous studies showed the presence of a “warm” gas halo (measured between 100,000 and more than one million kelvin), but the recent study is the first to indicate a “hot” gas halo.
NASA has also released an illustration of the gas cloud surrounding the Milky Way, showing the Milky Way as a small formation in the center with the Small and Large Magellanic Clouds galaxies nearby.