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The Fermi bubbles are two huge balls of gas and cosmic rays that tower over the Milky Way and cover an area that is about the size of the Milky Way itself. These gigantic room bubbles can be fed by a strong outflow of matter from the center of the Melkweg. | Credit: NASA Goddard
Two of the strangest structures in the Melkweg became even stranger.
Ballooning above and below the center of the Melkweg as a huge hourglass, the mysterious Fermi Bubbles looms up over our Melkweg. These huge double orbs of overheated plasma have been flowing from the galactic center for millions of years. Nowadays they include around 50,000 light years from point to point, which means that they are together half as long as the Milky Way is long.
Now scientists who study the confusing bubbles with the US National Science Foundation Green Bank Telescope in West Virginia have discovered slightly shocking: deep in the Superhot bubbles are gigantic clouds of cold hydrogen gas that have unexplained in an extreme environment.
According to the researchers, these bewildering clouds are probably the remains of much larger structures that were blown out of the center of the Galaxy a few million years ago.
“Think about it as dropping an ice cube in boiling water: a small melt quickly, but a larger one lasts longer -even if it dissolves,” said head study -author Rongmon Bordoloi, university teacher in the Department of Physics on North Carolina State University, live science. “We believe that these clouds can be remains of much larger structures that are currently being eroded by the galactic wind.”
The discovery could indicate that the central black hole of our Galaxy recently experienced a violent outburst of matter than previously thought, Bordoloi added. The research described by the clouds was published on July 7 in the Astrophysical Journal Letters.
Hide hydrogen gas clouds in the Fermi bubbles. | CREDIT: NSF/AUI/NSF Nrao/P.Toen
Astonishing bubbles
Hogging over the galactic center, the Fermi bubbles were discovered in 2010 by NASA’s Fermi Gamma-Ray Space Telescope. Although they are similar to our galaxy in size, the bubbles are only visible in gamma rays, and they overlap each other with a equally mysterious X -ray counterpart that is known as the EOTITA Bubbles.
These bubbles are incredibly hot, with the plasma that forms the Fermi bubbles that reach more than a million Kelvins (almost 2 million degrees Fahrenheit). It is thought that the bubbles are probably the result of an old, violent eruption from the central black hole of the Melkweg, which spit twin rays of matter above and below the galactic level at the same time, plunging in the process near the nearby matter and throwing it out in space.
According to the authors of the study, the newly discovered cold hydrogen clouds can be remains of part of that matter. Spotted with the Green Bank Telescope, the cold clouds vary from approximately 13 to 91 light years, making it many times larger than our solar system.
For those cold clouds to survive in the Superhot environment where they were discovered in the Fermi bubbles, about 13,000 light years above the center of the Galaxy must have been considerably larger when they were swept in the hanging of the bubbles for the first time, Bordoloi said.
“In principle, these clouds should not have survived that long,” he added. “Yet they exist, which gives us a kind of clock: their survival implies that the black hole in the center of the Melkweg broke out only a few million years ago. In cosmic terms that is an instant.”
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This discovery could help to resolve a great mystery about the Fermi bubbles by considerably limiting how old they are. This age, in turn, hints that the Monster Black Hole of our Galaxy, can experience violent, sporadic eruptions when large amounts of material fall into it, where the latter takes place more recently than previously thought. However, the precise schedule of outbursts in black holes in our Milky Way remains an open question.
“What is clear is that functions such as the Fermi bubbles – and more recently, the bubbles of the Erasta – suggest that the center of the Melkweg has been much more active in the recent past than we ever believed,” concluded Bordoloi.
