Hubble Helps Astronomers Observe Massive, Luminous Halo Around Andromeda Galaxy

The Hubble Telescope helped astronomers make an intriguing observation about our Milky Way Galaxy and neighbor, the Andromeda Galaxy.

According to NBC News, Hubble noticed a "halo" surrounding Andromeda extends about a million light years beyond its borders. The astronomers reasoned that if the Milky Way has such a halo, it may well be partly blended with Andromeda's.

The researchers published their work in the Astrophysical Journal.

"Halos are the gaseous atmospheres of galaxies," study lead author Nicholas Lehner, an astrophysicist at the University of Notre Dame (UND), said in a press release. "The properties of these gaseous halos control the rate at which stars form in galaxies.

"This is a new milestone because typically only one quasar is used to probe the halos of galaxies beyond the Local Group.

"Here we have assembled a large sample of quasars that directly demonstrate the true extent of the halo of a single massive galaxy."

These halos are also difficult to spot, but astronomers have been looking for them around other galaxies in the Local Group.

"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," study co-author J. Christopher Howk, associate professor of physics at UND, said in the release. "By measuring the dip in brightness, we can tell how much halo gas from M31 there is between us and that quasar."

The astronomers said the halo would appear 100 times larger than the moon if it was visible from the surface of the Earth. It would also appear quite luminous as well, containing as many stars as Andromeda has within it.

"Previous observations had only one target beyond each galaxy, and with a large sample of galaxies, they could infer that the gas could extend quite far from the galaxies," Lehner told NBC News. "However, these galaxies have different masses and stellar activities. Our observations show for the first time for a single galaxy that it has a massive halo as predicted by galaxy models."