The Andromeda Galaxy is surrounded by a massive halo of gas, according to data collected by the Hubble Space Telescope. This "atmosphere" of Andromeda is 1,000 times more massive, and six times larger than astronomers had predicted, reaching halfway to our own Milky Way galaxy. The feature is believed to contain at least half as much matter as the entire galaxy.
Astronomers believe study of the enormous cloud of gas could reveal previously unknown information about spiral galaxies, such as the Milky Way.
"Halos are the gaseous atmospheres of galaxies. The properties of these gaseous halos control the rate at which stars form in galaxies," Nicolas Lehner, an astrophysicist with the University of Notre Dame, said.
The Andromeda galaxy, also known as M31, is the nearest large galaxy to the Milky Way, and it ranks as the largest member of our own local group of galaxies that includes about 45 other known galaxies. This stellar family contains around 1 trillion stars, roughly twice the number present in the Milky Way. Sitting roughly 2.5 million light years away from our collection of stars, this galaxy is the most-distant object visible to the unaided human eye.
This gas cannot be seen over the vast amounts of space in which it is spread. Astronomers studied the light from 18 distant quasars as it passed through the intervening cloud. Certain wavelengths of light are absorbed by the material within the cloud. By measuring this drop in intensity, astronomers were able to determine the amount of material within the invisible mass.
"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," Lehner said.
If it were possible to see the halo around M31 from Earth, the feature would fill 50 degrees of the sky from one side to another - greater than the angular distance between the horizon and halfway up the sky.
Halos have been seen around other galaxies as well in previous studies. However, this was the first time such a massive feature has been seen in a galaxy so close to Earth. If the Milky Way galaxy also possesses a similar halo, the two galactic clouds may, one day, be in contact with one another in the reaches of deep space. The Milky Way and Andromeda are racing toward one another, and will collide in roughly 4 billion years, producing an even-more massive galaxy.
Discovery of the giant halo surrounding the Andromeda galaxy was published in The Astrophysical Journal.
Photo: NASA Goddard Space Flight Center | Flickr
