Scientists from the University of Notre Dame have discovered a massive halo of gas surrounding Andromeda, the galaxy nearest to Earth, which space experts believe could hold the secret to understanding the structure and evolution of spiral galaxies in the universe.

Nicolas Lehner, an astrophysicist from Notre Dame, led a team of researchers in studying a gaseous atmosphere located around 1 million light-years away from Andromeda. They were able to identify the phenomenon through the use of the Hubble Space Telescope operated by the National Aeronautics and Space Administration (NASA).

"The properties of these gaseous halos control the rate at which stars form in galaxies," Lehner said.

The galaxy of Andromeda, also known as Messier 31 or M31, is considered to be the largest member of a cluster of galaxies called the Local Group. This collection of galaxies includes the Milky Way as well as 45 other galaxies identified by scientists so far.

Messier 31 is estimated to contain a trillion stars in its sector, which is twice the number of stars in the Milky Way. The galaxy, located 2.5 million light-years away, is also believed to be 25 percent brighter than the Milky Way.

The researchers said the colossal halo could potentially contain enough mass in its diffuse gas equivalent to half of the stars found in the galaxy of Andromeda.

According to their findings, the halo serves as an important part of Andromeda. Despite being 100 times larger than the diameter of the moon, the gas constituting the halo is "invisible."

Lehner and his team studied the bright objects surrounding Andromeda that are affected by the halo's intervening gas. The researchers particularly noted quasars because of their highly luminous feature. The prevailing gas being sucked in by gigantic black holes in the area has caused the quasars to shine brightly.

"As the light from the quasars travels toward Hubble, the halo's gas will absorb some of that light and make the quasar appear a little darker in just a very small wavelength range," J. Christopher Howk, an associate professor from Notre Dame and a member of Lehner's team, said.

"By measuring the dip in brightness, we can tell how much halo gas from M31 there is between us and that quasar."

NASA's Hubble Space Telescope has allowed scientists to study various occurrences in space, including the formation of halos in distant galaxies.

The discovery of the halo around Andromeda marks the first massive one they have observed near the Earth beyond the Milky Way.

The University of Notre Dame study is published in The Astrophysical Journal.

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