Andromeda's Halo

[Recusant]

The galaxy Andromeda has a plasma halo, which has been mapped using the Hubble telescope.

"Hubble maps giant halo around Andromeda Galaxy" | PhysOrg

This illustration shows the location of the 43 quasars scientists used to probe Andromeda's gaseous halo. These quasars--the very distant, brilliant cores of active galaxies powered by black holes--are scattered far behind the halo, allowing scientists to probe multiple regions. Looking through the immense halo at the quasars' light, the team observed how this light is absorbed by the halo and how that absorption changes in different regions. By tracing the absorption of light coming from the background quasars, scientists are able to probe the halo's material. Credit: NASA, ESA, and E. Wheatley (STScI)

In a landmark study, scientists using NASA's Hubble Space Telescope have mapped the immense envelope of gas, called a halo, surrounding the Andromeda galaxy, our nearest large galactic neighbor. Scientists were surprised to find that this tenuous, nearly invisible halo of diffuse plasma extends 1.3 million light-years from the galaxy—about halfway to our Milky Way—and as far as 2 million light-years in some directions. This means that Andromeda's halo is already bumping into the halo of our own galaxy.

They also found that the halo has a layered structure, with two main nested and distinct shells of gas. This is the most comprehensive study of a halo surrounding a galaxy.

"Understanding the huge halos of gas surrounding galaxies is immensely important," explained co-investigator Samantha Berek of Yale University in New Haven, Connecticut. "This reservoir of gas contains fuel for future star formation within the galaxy, as well as outflows from events such as supernovae. It's full of clues regarding the past and future evolution of the galaxy, and we're finally able to study it in great detail in our closest galactic neighbor."

[. . .]

Through a program called Project AMIGA (Absorption Map of Ionized Gas in Andromeda), the study examined the light from 43 quasars—the very distant, brilliant cores of active galaxies powered by black holes—located far beyond Andromeda. The quasars are scattered behind the halo, allowing scientists to probe multiple regions. Looking through the halo at the quasars' light, the team observed how this light is absorbed by the Andromeda halo and how that absorption changes in different regions. The immense Andromeda halo is made of very rarified and ionized gas that doesn't emit radiation that is easily detectable. Therefore, tracing the absorption of light coming from a background source is a better way to probe this material.

[Continues . . .]

Only the abstract of the paper is available.

[xSilverPhinx]

Like a galactic ghost.

[No one]

[xSilverPhinx]

Not that ghost. 

[Randy]

[Tank]

Fascinating.