Astronomers have determined the age of the Fermi bubbles – giant structures observed in the central zone of the Milky Way. It is assumed that 2.6 million years ago, a supermassive black hole experienced a burst of activity lasting 100 thousand years, which gave rise to two jets that injected high-energy particles into the medium of the Milky Way.
What are the Fermi Bubbles?
In 2010, the Fermi Gamma-Ray Telescope discovered a new structural element in the Milky Way called the Fermi Bubbles. They are located perpendicular to the plane of the galaxy, radiate in the microwave, X-ray, and gamma-ray ranges, and have huge dimensions – the total length is estimated to be almost half the diameter of the Milky Way.
It is assumed that they could have arisen due to the activity of a supermassive black hole at the center of the Milky Way or due to a burst of star formation.
In December 2020, the first version received new confirmation when the Spektr-RG X-ray observatory using the eROSITA telescope discovered other bubble-like structures in the center of our galaxy, the morphology of which was remarkably similar to Fermi bubbles.
Scientists may have found an explanation for the bubbles in the center of the Milky Way
A team of astronomers led by Karen Yang of National Tsinghua University set out to understand the nature of the Fermi bubbles and eROSITA using 3D computer simulations of the energy release in the central zone of the Milky Way.
The scientists considered two possible hypotheses for the origin of the bubbles – the lepton jet model, which is associated with recent black hole activity, and the cosmic ray proton acceleration model due to shock waves or turbulence, which suggests star formation and supernova explosions inside the bubbles.
The scientists concluded that both types of bubbles and microwave radiation from the central region of the Milky Way can be explained by a single activity event of the central supermassive black hole, which led to a bipolar jet that injected protons of cosmic rays responsible for gamma radiation into the Milky Way’s medium.
This phenomenon began 2.6 million years ago and lasted 100 thousand years. At the same time, due to the large pressure contrast in the jets with respect to the environment, the jet matter expanded into a pair of bubbles, similar to radio bubbles observed in galaxy clusters, so the surfaces of the eROSITA and Fermi bubbles correspond to the forward shock wave.
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Sources:
• Choi, C. Q. (2022, March 9). Giant radiation bubbles created by Monster Black Hole Feeding Frenzy, new study suggests. Space.com.
• O’Neill, M. (2022, March 9). Gigantic bubbles at center of milky way caused by powerful jet of energy from supermassive black hole. SciTechDaily.
• Starr, M. (n.d.). Giant bubbles expanding from the milky way could be explained by a single event. ScienceAlert.
• University of Wisconsin-Madison. (2022, March 9). Massive bubbles at center of milky way caused by supermassive black hole. News.
• Yang, H.-Y. K., Ruszkowski, M., & Zweibel, E. G. (2022, March 7). Fermi and EROSITA bubbles as relics of the past activity of the galaxy’s central Black Hole. Nature News.
