Our Galaxy Could be Mixing With Andromeda's Supersized Halo

The Andromeda galaxy, the nearest spiral galaxy to our Milky Way, is sporting a massive halo of hot gas spanning a million light-years into intergalactic space.

The NASA/ESA Hubble Space Telescope stumbled across this finding after archival data of distant quasars was analyzed.

“Halos are the gaseous atmospheres of galaxies. The properties of these gaseous halos control the rate at which stars form in galaxies according to models of galaxy formation,” said Nicolas Lehner, of the University of Notre Dame, Ind., lead author of the new study published in The Astrophysical Journal.

This halo is a big deal; it is estimated to contain half the mass of all the stars in the galaxy itself and is 1,000 times more massive than previous estimates suggested. Galactic halos are thought to form the same time as their host galaxies and Lehner’s team have determined that Andromeda’s halo is enriched with heavy elements.

These heavy elements came from periods of intense supernova activity — when massive stars run out of fuel and explode — within the galactic disk and powerful stellar winds blew the heavy element-laced gases into intergalactic space, into Andromeda’s halo. It is thought that nearly half of all the heavy elements generated by supernovae over Andromeda’s lifetime can be found in this extended halo.

Interestingly, if our galaxy also possesses a halo comparable to Andromeda’s it is conceivable that both halos are currently in contact and mixing galactic material. Both galaxies are currently on a collision course and expected to merge in 4 billion years time. Therefore, understanding halo dynamics may reveal that, well before galactic mergers, the respective galaxies’ halos merge quiescently.

The discovery of the Andromeda halo’s immense scale and mass came from the study of distant quasars. Over the past 5 years, Hubble has amassed a wealth of quasar data and the researchers were able to focus on quasar data in the direction of Andromeda. As Andromeda’s halo is dark, it was only detectable by the dimming of quasar emissions. As several quasars have been studied beyond Andromeda, a picture of the halo’s landscape could be constructed (as described in the diagram below.

Read more at Discovery News