The halo of the Andromeda galaxy borders on that of the Milky Way

Thanks to the Hubble telescope, NASA scientists have managed to map the immense halo of gas surrounding the Andromeda galaxy. This one is so gigantic that it would come into contact with the halo of the Milky Way

Andromeda, our closest galactic neighbor, is twice the size of our own galaxy. It is located at such a small distance from the Milky Way that if its luminosity was sufficient, we would see it occupy several times the diameter of the Moon in the night sky ! But its gigantism also extends beyond the borders of the visible: the halo of plasma that surrounds it extends at a distance between 1.3 million and two million light-years from the galaxy itself. It is so large, say the researchers, that it comes, in certain directions, to touch the halo of the Milky Way.

Echo of past stars, reservoir of future stars

Through a program called Amiga ( Absorption Map of Ionized Gas in Andromeda ), researchers were able to map this cosmic giant using data collected by the Hubble Space Telescope . This is indeed able to observe ultraviolet rays , usually absorbed largely by the Earth ‘s atmosphere . By measuring the radiation of 43 quasars located beyond Andromeda, they were able to estimate the dimensions of the halo according to the quantity of light that it allowed through. The team was able to see that it was made up of two main layers.

” We have discovered that the inner layer spans about half a million light years is much more complex and dynamic ,” comments Nicolas Lehner , head of the study published in The Astrophysical Journal . The inner layer is smoother and warmer. This difference is likely the result of the impact of the activity of a supernova in the galaxy’s disk, more directly affecting the inner part of the halo. This hypothesis could be confirmed by the detection of heavy metals , signature of the recent death of a star.

Discover Andromeda to understand the Milky Way

It is difficult for us to analyze the signature of the halo of the Milky Way from inside the galaxy. However, researchers believe that it could be similar to the Andromeda halo, which bears many similarities to our galaxy. In four and a half billion years, scientists predict that the two spiral structures will collide to form a single giant elliptical galaxy . “ The Amiga project also gave us a glimpse into the future, ” adds Lehner.

“  Understanding the immense halos of gas surrounding galaxies is crucial ,” says co-author Samantha Berek. This gas tank contains the fuel necessary for the formation of future stars inside the galaxy, and the products of events such as supernovas. It contains many clues concerning the past and the future evolution of the galaxy, and we are finally able to study it in all its details in our galactic neighbor

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