A team of astronomers used NASA’s Chandra X-ray Observatory to find evidence that the Milky Way is wrapped in an enormous halo of gas that has a radius of at least 300,000 light years but it could be much bigger. The size of this halo is therefore so big that it includes the Large and Small Magellanic Clouds, two small galaxies near – of course in astronomical terms – the Milky Way.

Five researchers used data from the Chandra X-ray Observatory with two other space telescopes: ESA’s XMM-Newton and Japanese Suzaku to estimate the temperature, the extent and mass of this halo. Chandra observed eight X-ray sources at distances of hundreds of millions of light years. The data revealed that X-rays were absorbed selectively by oxygen ions in the vicinity of the Milky Way. Scientists have determined that the temperature of the absorbing halo is between 1 and 2.5 million degrees Kelvin.

The gas of the halo is regularly hit by cosmic rays and other energy charged radiation and this is the reason why such enormous masses can reach temperatures hundreds of times that of the surface of the Sun.

Other research has shown that there are galaxies shrouded in gas at temperatures between 100,000 and 1 million degrees Kelvin and some studies have indicated the presence of gas with temperatures over 1 million degrees Kelvin. This new research shows evidence that the halo of hot gas surrounding the Milky Way has a mass much greater than those other hot halos.

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To get an estimate of the mass of the halo that wraps the Milky Way data from the space telescopes Chandra, XMM-Newton and Suzaku have been used to evaluate the absorption produced by oxygen ions. The researchers concluded that the mass of gas is more than ten billion times that of the Sun and could reach sixty billion solar masses.

The estimation of the mass depends on factors such as the ratio between oxygen and hydrogen, which is the dominant element. At least for now it’s not very precise but it’s important because for several years astronomers were looking for a large amount of baryonic matter, which is the ordinary one composed of particles such as protons and neutrons. These huge halos may contain the missing baryonic matter and only because of their low density they weren’t identified earlier.

This research is linked to that of dark matter, which may partly hide in these massive halos that surround galaxies. The search continues, also to understand how these halos form. The answer may help us better understand the formation of the “normal” part of the galaxies composed by stars and planets.