A strange shield of supercharged gas protects dwarf galaxies from being torn apart by the Milky Way’s gravitational pull, 30 years of observations by the Hubble Space Telescope reveal.
For years, astronomers have struggled to explain why the Big and Small Magellanic Cloudstwo tiny galaxies orbiting Milky Wayform again stars. The two dwarfs galaxies have been orbiting our galactic home for billions of years, according to research, during which the much more massive Milky Way’s gravitational pull pulled gas from the two smaller galaxies, creating a trail in their wake. In theory, this loss of gas should stifle star birth, but small satellite galaxies have still managed to maintain vigorous star formation.
“A lot of people were struggling to explain how these streams of material could be there,” said Dhanesh Krishnarao, an assistant professor at Colorado College, in a statement. “If this gas was removed from these galaxies, how do they still form stars?”
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This has led astronomers to theorize that the Large and Small Magellanic Clouds may be shielded by a cosmic “shield” – called the Magellanic Corona – made up of supercharged gas with temperatures of half a million degrees.
So far, evidence for Magellanic corona sightings has been elusive, but new research based on 30 years of observations by the The Hubble Space Telescope and the now retired Far Ultraviolet Spectroscopic Explorer (FUSE) satellite may have changed that.
While analyzing the data, Krishnarao and his colleagues discovered that the Large and Small Magellanic Clouds – known collectively as the Magellanic System – are indeed surrounded by a shield of supercharged hot gas that envelops the clouds. dwarf galaxies, preventing their star-forming gas from being siphoned off. through the Milky Way. This, in turn, helps them continue to form stars.
“Galaxies wrapped themselves in gaseous cocoons, which act as defensive shields against other galaxies,” Andrew Fox, an astronomer at the Space Telescope Science Institute in Maryland, who was part of the team, said in the statement. .
This cosmic shield was difficult to detect because despite stretching the Magellan system for 100,000 Light years, the crown of Magellan is almost invisible. If not, it would cover much of the southern sky.
The team believe galactic coronas like the recently discovered Magellanic corona are the remnants of primordial gas clouds that undergo gravitational collapse and form galaxies. These coronas have been spotted around other galaxies, but have never been seen around one so close to the Milky Way and therefore in such detail.
“There are many predictions from computer simulations of what they should look like, how they should interact over billions of years,” Krishnarao said. “From an observational point of view, we can’t really test most of them because dwarf galaxies are usually too hard to detect.”
Scouring the Hubble/Fuse data, the astronomers were specifically looking for ultraviolet observations of quasars located billions of light-years behind Magellan’s corona.
At the heart of many galaxies are active galactic nuclei (AGNs), some of which are quasars powered by gas-eating supermassive black holes. When they swallow this material, black holes emit so much energy that they shine brighter than all the stars in their respective galaxy combined.
The team therefore reasoned that the invisible corona protecting the foreground galaxy (from the observer’s perspective) should make itself apparent through the effect it has on the quasar light passing through it, appearing as a distorting fog obscuring and absorbing distinct patterns of bright light from background quasars.
Astronomers examined ultraviolet light patterns from 28 different quasars, which allowed them to characterize the material surrounding the Large Magellanic Cloud.
The quasar light spectrum was found to contain the elemental “fingerprints” of carbon, oxygen and silicon in a halo of hot plasma surrounding the Large Magellanic Cloud indicating the presence of the Magellanic Corona.
“It’s a perfect telltale signature that this crown is really there. It really envelops the galaxy and protects it,” Krishnarao said.
The astronomer also explained how a thin cloud of gas could protect a galaxy.
“Anything that tries to pass through the galaxy has to pass through this material first, so it can absorb some of that impact,” he said. “Also, the corona is the first material that can be extracted. By giving up some of the corona, you protect the gas that is inside the galaxy itself and is capable of forming new stars. “
The team’s research is published in the September 28 edition of the journal Nature (opens in a new tab).
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