An international team of astronomers has mapped the gas halo of the Andromeda galaxy. They used radiation from 43 quasars in it to analyze the deflection of light as it passes through streams of gas using a spectrograph on the Hubble telescope. It turned out that this shell of our neighboring galaxy is huge and stretches for millions of light years.
With a detailed study, scientists have found out that the Andromeda galaxy has two gas shells. The inner one, stretching for half a million light years, is constantly exposed to the black hole in the center of the galaxy, so it is very dynamic and has a complex structure, various as yet unexplored processes take place in it. The outer shell, on the contrary, is cold and calm, but it is several times larger than the inner one, its dimensions vary in the range of 1.3-2 million light years.
Two million light-years is such a great distance from the center of the Andromeda galaxy that its gas halo in this region of space already intersects with a similar gas envelope of the Milky Way. The galaxies themselves will not collide very soon, but their distant gas layers are already actively pressing against each other, so with a reservation, the process of collision of galaxies can be called launched. While this is practically not manifested in any way, but scientists cherish the hope in the future to extract a lot of useful data, observing process.