A group of scientists has discovered a massive halo of gas encircling the Andromeda galaxy, the nearest major galaxy to our own Milky Way.

The scientists used NASA’s Hubble Space Telescope to spot the ring, which extends out about a million light-years beyond Andromeda, about half the distance to the Milky Way, according to an International Business Times report.

The Andromeda galaxy is the largest galaxy in what is called the Local Group, a collection of galaxies that includes the Milky Way as well as 45 other galaxies. Andromeda has a trillion stars and is about 25 percent brighter than the Milky Way.

This discovery of a gas halo could help astronomers understand the structure and formation of giant spiral galaxies — both Andromeda and the Milky Way are considered spiral galaxies.

The study, which was published in the Astrophysical Journal recently, found that the halo has 100 times the diameter of the moon, and the gas is invisible, so scientists had to use quasars — distant star-like objects that shine brightly due to gas falling into a supermassive black hole — to make their observations.

Nicolas Lehner, the lead author of the study and an astrophysicist at the University of Notre Dame, said that halos are essentially the gaseous atmospheres of galaxies, and they control the rate of star formation within galaxies.

Scientists believe that the Andromeda Galaxy will collide with the Andromeda galaxy in about five billion years. By that time, massive galaxies in the universe will have stopped making their own stars and will rely on consuming other galaxies in order to grow.

If the Milky Way has a similar halo to Andromeda’s, the halos of both galaxies could merge much sooner than the galaxies themselves, creating one big elliptical galaxy.