Galactic halos are both more massive and more complex than scientists realized, according to new observations from Hubble Space Telescope.
The revered telescope looked at the neighboring galaxy Andromeda, using dozens of different quasars to map the galactic halo. Andromeda, more officially known as M31, is a spiral galaxy of approximately the same size as Milky Way a galaxy in which we live, with about 1 trillion stars. Cosmically, it is next door, only 2.5 million light-years away, which means that Hubble can study its halo with unprecedented detail.
“This is truly a unique experiment, because with Andromeda alone we have information about its halo in not just one or two views, but over 40,”
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These lines of observation are made up of active black holes located in the heart of galaxies on the opposite side of Andromeda. These objects, the so-called quasars, produce a lot of light, and it is easier for scientists to study how the gases in a halo absorb some of that light than to study the halo itself. So Hubble focused his ultraviolet gaze on 43 different quasars beyond Andromeda and analyzed their light to map the gaseous carbon, silicon, and oxygen in the halo.
The Andromeda Galaxy the halo is not just a convenient target; scientists also believe that given the other similarities between our neighbor and our own galaxy, the halo of Andromeda may teach us about the Milky Way’s own halo, which is difficult to explore from the galaxy.
“Understanding the vast halos of the galaxies surrounding the gas is extremely important,” said Samantha Berek, who worked on the study as a student at Yale University in Connecticut, in a statement. “This gas tank contains fuel for future star formation in the galaxy, as well as leaks from events such as supernovae. It is full of clues about the past and future development of the galaxy, and we are finally able to study it in great detail in the nearest our galactic neighbor. “
Researchers have found that the halo itself extends far beyond space, as expected, a whopping 1.3 million light-years from the galaxy – and in some places more than 2 million light-years. If human eyes can see it, it will be three times wider than The big bear, according to NASA. More clearly, the halo of Andromeda covers more than half the distance between Andromeda and the Milky Way, suggesting that the two halos mix.
The new study also found that the structure of the Andromeda halo is also more complex than expected so far, with two separate layers. “We find that the inner shell, which extends to about half a million light-years, is far more complex and dynamic,” Lehner said. “The outer shell is smoother and hotter.”
Lehner and colleagues suspect that the two-component structure of the halo may have been caused by stellar explosions called supernovae in Andromeda’s main disk, which would have a more dramatic effect on the inside of the halo, shaking it than on the outside. Supernova are also a key mechanism for the propagation of heavy elements, such as those identified by researchers in this study, into space.
The study relies on Hubble’s ability to see in ultraviolet light, a rare talent among current space telescopes. But even Hubble can create such a detailed map of the halos of very close galaxies; most other galaxies do not have enough visible quasars lurking in their distant lands for the telescope to focus on them.
But if we look at just one galactic halo, it may overlap with our own. And eventually we will be even closer to the halo of Andromeda, as our two galaxies slowly eject into each other and collide in a few billion years.
The study is described in paper published August 27 in The Astrophysical Journal.
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