You may have seen Andromeda galaxy (M31) without realizing it. The vast spiral galaxy appears as a gray, spiral bubble in the night sky, visible to the naked eye in perfect condition. It is the largest galaxy near us, and astronomers have studied it a lot.
Now astronomers have been using the Hubble Space Telescope to map Andromeda’s vast hot gas.
Scientists call the halo of the gas around the galaxy the circular medium (CGM). CGM is contagious, almost invisible. But as scientists acquire the technology to study it more closely, they begin to understand the key role it plays in the evolution of the galaxy. They think that CGM is an important source of star-forming material and that it regulates the distribution of gas in a galaxy.
In a new study, a team of researchers used Cosmic Origins Spectrograph Using the Hubble Space Telescope (HST) to create a CGM map of Andromeda (COS). Title of the study “Project AMIGA: Andromeda’s Circular Media.The main author is Nicola Lehner from the University of Notre Dame in Indiana. The study was published in The Astrophysical Journal.
Study shows that the halo of Andromeda is the largest object in the night sky, which we cannot see. It extends 1.3 million light-years from the center of Andromeda, about halfway to our galaxy. In some directions, it extends further up to 2 million light years. The halo of Andromeda is actually colliding with the halo of the Milky Way.
The CGM has more details than the researchers thought. It has two layers: the inner shell of the gas is built into the outer shell. The inner shell is very dynamic, and the outer shell is hot and soft. The team of researchers believes that the inner shell is very dynamic and turbulent as it exits supernovae.
“The inner shell, which lasts about half a million light years, is very complex and powerful,” explained Nicola Lehner, head of research at the University of Notre Dame in Indiana. “The outer shell is softer and warmer. This difference directly affects the inner halo as a result of the impact of supernova activity on the galaxy,” Lehner said. News release.
This is not the only dynamic state of the inner halo that points to supernovae. It is also a mixture of gas. The team discovered several heavy elements in the gas that are formed in the hearts of massive stars, and they propagate into space by exploding supernovae.
The gas in the CGM automatically releases some energy, but it is very difficult to see. The researchers studied ultraviolet light from distant quasars as it passed through the halo. That ultraviolet light is absorbed by the Earth’s atmosphere so it cannot be seen from the ground. But Hubble can see it from its position in low-Earth orbit (Leo.).
In our view the team discovered 43 quasars that were “behind” Andromeda. Because they are scattered across the width and breadth of the galaxy, researchers have been able to study the halo in many places. They observed how UV light is absorbed differently from distant quasars in different parts of the CGM. The team used Hubble’s COS to detect ionized gas from carbon, silicon and oxygen.
This is not the first time that leading researcher Lehner Andromeda has observed light from distant quasars. In 2015 he and his colleagues published a pilot study of Andromeda based on light coming from six quasars. That study showed how big and huge CGM Andromeda is, but it did not reveal all the problems. That work ”Evidence for a massive, expanded circular medium around the Andromeda Galaxy”And also published in The Astrophysical Journal.
“Previously, the galaxy had the lowest information in 1 million light-years — only six quasars. This new project provides additional information about this inner part of Andromeda’s halo, ”said J. J. Notre Dame, co-researcher. Christopher Hoag explained. “It is important to study the gas at this radius because it indicates the influence of a gravitational force on the andromeda.”
The team also measured the velocity of the gas in the inner and outer haloes. They determined that the inner shell was more powerful than the outer shell. The inner shell shows many velocity components, while the outer shell shows only one velocity component. Velocity measurements allowed to determine whether the outer halo was gravitationally bound to the andromeda.
Samantha Perek, a co-researcher at Yale University in New Haven, Connecticut, explained: “Understanding the vast gases surrounding galaxies is very important. “This gas reservoir contains fuel for future star formation within the galaxy, as well as for eruptions from supernova-like events. It is full of clues about the past and future evolution of the galaxy, and finally it can be read in detail in our nearest galaxy neighborhoods. ”
Andromeda is really the only opportunity to study things like a CGM in detail. Our position within the Milky Way makes it possible to study the Milky Way’s own CGM. No other large galaxy is capable of studying our current technology in this way. Distant galaxies appear to be very small due to the lack of adequate background quasars for spectroscopy. Each quasar behind a galaxy provides scientists with a line of sight.
“This is truly a unique experiment because with Andromeda only information about its halo contains not one or two views, but more than 40,” Lehner explained. “It’s amazing to capture the problem of a galaxy beyond our own Milky Way.”
Although we cannot directly read the CGM of the Milky Way, the researchers say that they can speculate on some of its properties based on this study. In their study, they write, “MW may contain similarly cold and hot-hot ionized CGM,” and the CGM of the Milky Way and Andromeda “often interacts with each other.”
As it stands now, Andromeda is the only galaxy that can be explored in this way. But in the future, that will change. Such as future UV space telescopes Play (Large UV / Optical / IR Surveyor), with its massive 15m mirror, should allow scientists to read the CGMs of galaxies outside our local group. In that sense, this study gives us an overview of some of the possible outcomes in the future.
“So the plan Amika It also gives us a vision of the future, ”Lehner said.