The Large and Small Magellanic Clouds are the two closest galaxies to the Milky Way. And when they were gravitated toward our galaxy, billions of years ago, as they orbited each other, they tore apart, leaving trails of gaseous debris behind, RT reported.
These dwarf galaxies are still intact and undergoing active star formation, which baffles astronomers.
“A lot of people have been struggling to explain how these streams of material might exist,” said Danesh Krishnaraw, an assistant professor at the College of Colorado. “If this gas is removed from these galaxies, how do stars still form?”
With the help of data from NASA’s Hubble Space Telescope and a retired satellite called the Ultraviolet Spectrograph Explorer (FUSE), astronomers led by Krishnarau finally found the answer: the Magellan system is surrounded by a “coron” (or halo), a shield from Supercharged hot gas.
This shield limits the Small and Large Magellanic Clouds, preventing the Milky Way from withdrawing its gas supplies, thus allowing them to continue forming new stars.
The discovery, which was recently published in the journal Nature, addresses a new aspect of galactic evolution. “Galaxies enclose themselves in gaseous cocoons, which act as defensive shields against other galaxies,” said study co-author Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland.
Astronomers predicted the existence of the corona several years ago. “We knew that the Large Magellanic Cloud would have to be massive enough for a corona to occur,” explained Elena Dungia, a research associate at the University of Wisconsin-Madison.
However, although the corona extends more than 100,000 light-years from the Magellanic Cloud and covers much of the southern sky, it is virtually invisible. The mapping required searching for 30 years of archived data to make appropriate measurements.
Scientists believe that the galaxy’s corona is the remnant of the primordial gas cloud that collapsed to form the galaxy billions of years ago.
Although the halo has been seen around distant dwarf galaxies, astronomers had never before been able to observe one in such great detail.
“There are a lot of predictions from computer simulations about what they should look like and how they should interact over billions of years, but in terms of observation we can’t really test most of them because dwarf galaxies are usually very difficult to detect,” Krishnaraw explained. Right on our doorstep, the Magellanic Clouds provide the perfect opportunity to study how dwarf galaxies interact and evolve.
Looking for direct evidence of Magellan’s corona, the team combed the Hubble Archives and the Ultraviolet Spectroscopic Explorer for ultraviolet observations of quasars billions of light years behind.
Quasars, or quasars, are the extremely bright cores of galaxies that harbor massive active black holes.
The team concluded that although the corona would be too faint to be seen on its own, it should be visible as a kind of haze that blocks and absorbs distinct patterns of bright light from background quasars.
Hubble’s observations of quasars have been used in the past to map the corona surrounding the Andromeda galaxy (our neighbor’s Andromeda galaxy).
By analyzing the patterns in ultraviolet light from 28 quasars, the team was able to detect and characterize the material surrounding the Large Magellanic Cloud and confirm the presence of the corona.
As expected, the quasar’s spectra are imprinted with distinctive fingerprints of carbon, oxygen and silicon that make up the halo of hot plasma that surrounds the galaxy.
The team also discovered that the amount of gas decreases with distance from the center of the Large Magellanic Cloud. “It’s a perfect stimulus signature that this corona is really there, it’s really the cocoon of the galaxy and its protection,” Krishnaaru noted.