Fermi bubbles: two giant structures of hot gas
Above and below the plan of the Milky Way, Fermi Bubbles extends into space for more than 25,000 light-years each. Hints of their presence were already discovered by the Rosat X-ray telescope in the 1990s. But their existence was confirmed in 2010. By a team of scientists working with the Fermi telescope.
Also read: Two giant bubbles in the heart of our galaxy created by a supermassive black hole
The Fermi telescope, the full name Fermi Gamma-ray Space Telescope, was launched in June 2008 by NASA. its goal? Study some of the most violent phenomena that take place in space. Such as blazers produced by supermassive black holes or gamma-ray bursts. This telescope works within gamma rays, classified among the most powerful rays in the universe.
It was by analyzing the diffuse gamma radiation produced by the interaction between the accelerated electrons in the interstellar medium and low-energy photons that they discovered the Fermi bubbles.
These two huge patches, resembling a dumbbell, emit gamma rays on either side of the galactic plane. The latter is produced by electrons that are accelerated to 500 gigaelectron volts. Although their origin remains unknown, several hypotheses have been formulated! A rapid release of an incredible amount of energy from the supermassive black hole Sagittarius A at the center of the galaxy. Or the result of what astronomers call a “starburst.” That is, the formation and explosion of many massive stars at the same time.
Fermi bubbles, which are invisible to the human eye, contain very hot gases and heavy metallic elements. These are probably silicon, aluminum and carbon.
Fermi’s high speed clouds are bubbling
In astronomy, a high-velocity cloud is a mass of gas whose particles can reach speeds of over 200,000 km / h. Scientists have discovered one in the galactic halo that encloses the Milky Way. These gas clouds can be massive, as they can reach millions of times the mass of the Sun in certain galaxies.
Previous research has shown that Fermi bubbles, which are also gas sheaths, contain high-velocity gas clouds with temperatures of up to 8 million Kelvin. These formations at the base of the Fermi bubbles have been named Fermi Bubble High Velocity Clouds. Until the publication of this research in Nature astronomy, little work has been done to try to understand the composition of these gas clouds.
For many astronomers, these hot gas formations in the Fermi bubbles consist of material thrown up by the growth disk. This orbits at phenomenal speeds around the supermassive black hole in the center of the galaxy. Others believe that these gas clouds are produced by matter emitted directly from the black hole.
As part of this new study, the researchers tried to understand the composition of these high-velocity gas clouds of Fermi bubbles.
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Determine the metallic percentage to understand the origin of these gas clouds
Researchers from the Space Telescope Science Institute in Baltimore, North Carolina State University, and researchers from several other universities across the United States tried to determine the percentage of metals present in these high-speed clouds.
In order to confirm that these metallic elements come from the immediate environment, i.e. from the accretion disk or from that which is rejected by the black hole, the metallic proportions must be relatively dense. If these proportions are far apart, astronomers will have to come up with a different theory to explain the origin.
As astronomers analyzed new and old data received by several telescopes studying these high-speed clouds, to their amazement, astronomers found that in most cases there was no correspondence. This therefore indicates that the material or part of the material included in the composition of these gaseous clouds comes from a more distant place.
Scientists already have their own idea of the external origin of this matter: the galactic halo. It is a large area of hot gas that surrounds the Milky Way. All galaxies are surrounded by a galactic halo. They are considered by astronomers as important elements in the study of the universe. Why ? Because they can provide significant information about the formation of galaxies. Some astronomers also suspect them of containing baryonic substance.
Also read: The Magellanic Current may collide with the Milky Way much earlier than expected
Source: Ashley, T., Fox, AJ, Cashman, FH et al., “Different Metallicities of Fermi Bubble Clouds Indicate Dual Origin in the Disc and Halo”. Nature Astronomy, (2022), https://doi.org/10.1038/s41550-022-01720-0