For billions of years, the Large and Small Magellanic Clouds, the largest satellite galaxies of the Milky Way, have undergone perilous journeys. Orbiting each other as they pull toward our home galaxy, they begin to unravel, leaving behind a trail of gaseous debris. remains and active star formation is underway.
“A lot of people have had a hard time explaining how these streams of material are there,” said Danesh Krishnarao, an assistant professor at the University of Colorado. How is it still forming stars if removed from
With the help of data from NASA’s Hubble Space Telescope and a retired satellite called the Far Ultraviolet Spectrometer (FUSE), a team of astronomers led by Krishnarao finally found the answer: hot supercharged gas. This would cocoon the two galaxies, preventing their gas supply from being siphoned off by the Milky Way and allowing them to continue forming new stars.
This discovery, just published in Nature, addressing new aspects of galactic evolution. “Galaxies are wrapped in gaseous cocoons that act as defensive shields against other galaxies,” said co-investigator Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland.
Astronomers predicted the existence of the corona years ago. “Including the corona in our simulation of the Magellanic Cloud falling into the Milky Way shows that for the first time we can explain the mass of the extracted gas,” explained university collaborator Elena Dongia. Wisconsin – Madison. “We knew the Large Magellanic Cloud was big enough to have a corona.”
But the corona, which extends over 100,000 light-years from the Magellanic Clouds and covers much of the southern sky, is practically invisible. Mapping it would have required him to scrutinize 30 years of archival data for the right measurements.
Researchers believe that the galaxy’s corona is the remnant of a primordial gas cloud that collapsed into the galaxy billions of years ago. Corona was seen farther away, dwarf galaxyastronomers have never been able to probe in such detail.
“There were many predictions computer simulation We study what they should look like and how they should interact over billions of years, but dwarf galaxies are usually too hard to detect, so observationally test most of them. You can’t. The Magellanic Cloud provides an ideal opportunity to study how dwarf galaxies interact and evolve.
Seeking direct evidence for the Magellan corona, the team combed through the Hubble and FUSE archives and made ultraviolet observations of quasars billions of light years behind it. A quasar is a very bright core of a galaxy that hosts a massive active black hole. The team reasoned that while the corona is too dim to be seen in isolation, it should appear as a kind of fog that obscures and absorbs distinct patterns of bright light from background quasars. Observations have been used in the past to map the corona surrounding the Andromeda galaxy.
By analyzing the pattern of ultraviolet rays From 28 quasars, the team was able to detect and characterize material surrounding the Large Magellanic Cloud and confirm the presence of a corona. The carbon, oxygen, and silicon that make up the plasma halo are imprinted with distinct features.
Detecting the corona required a very detailed ultraviolet spectrum. “Hubble and FUSE resolution were very important for this study,” he explains Krishnarao. “Corona gas is very diffuse and almost non-existent.” Additionally, it mixes with other gases, such as streams drawn from the Magellanic Clouds and material from the Milky Way.
By mapping the results, the team also found that the amount of gas decreases with distance from the center of the Large Magellanic Cloud. Krishnarao said it was “perfect proof that this corona really exists.” “It really envelops and protects the galaxy.”
How can such a thin shroud of gas protect the galaxy from destruction?
“Anything trying to enter the galaxy must first pass through this material, so it can absorb some of its impact,” Krishnarao explained. “In addition, corona is the first substance that can be extracted. corona, inside the galaxy itself, protecting gas that can form new stars. ”
Dhanesh Krishnarao et al, Observations of the Magellanic Corona, Nature (2022). DOI: 10.1038/s41586-022-05090-5
Quote: Hubble Detects Protective Shield Guarding Pair of Dwarf Galaxies (September 28, 2022)
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