Thanks to the Hubble Space Telescope, new observations of Andromeda's galactic halo have been discovered, and they're massive.
The telescope was able to observe our neighboring galaxy, Andromeda or M31, using different quasars to map out its galactic halo. Sitting at roughly 2.5 million lightyears away, Andromeda is the closest galaxy to ours, the Milky Way, and so can be observed in clear detail.
The findings were published in the Astrophysical Journal on Thursday.
"This is groundbreaking for capturing the complexity of a galaxy halo beyond our own Milky Way," said Nicolas Lehner in a NASA statement, who is an astrophysicist at the University of Notre Dame in Indiana.
"This is truly a unique experiment because only with Andromeda do we have information on its halo along not only one or two sightlines, but over 40."
These sightlines are active black holes within the heart of the galaxy, called quasars. They help scientists study how gasses in the halo absorb light, which sheds light on the galactic halo itself.
In order to do this, the Hubble telescope pointed its focus to these 43 quasars past Andromeda, which mapped out what was in the halo. By understanding what lies in this galactic halo, scientists believe it'll help them to better comprehend our own galaxy's halo, which is tricky to study from within the same galaxy.
Upon observing Andromeda's halo, the researchers discovered that the halo stretched far further than they previously imagined: a massive 1.3 million lightyears away from the galaxy. It even reaches 2 million lightyears away in certain spots.
The team also discovered more information about the halo's structure, which turns out to be far more complex than they thought.
Lehner explained "We find the inner shell that extends to about a half million light-years is far more complex and dynamic. The outer shell is smoother and hotter."
The team was able to discover all of this thanks to Hubble's ultraviolet light capabilities.