Thursday, February 2, 2023

Study explains the mysterious gamma-ray-producing bubbles surrounding the galactic center

Evidence shows strong outflowing winds responsible for the “Fermi bubbles”.

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The Fermi bubbles are large gamma-ray-emitting structures. They are symmetric about the Galactic Centre (GC), and their creation is attributed to intensive energy injection at the GC.

In this study, a scientist from Tokyo Metropolitan University has shown that large gamma-ray emitting bubbles around the center of our Galaxy were produced by fast-blowing outward winds and the associated “reverse shock.”

The scientist mainly focused on the non-equilibrium X-ray gas structures associated with the bubbles. They show that a combination of the X-ray gas’s density, temperature, and shock age profiles can be used to distinguish the energy-injection mechanisms.

Numerical simulations accurately reconstructed the temperature profile that an X-ray telescope recorded. This study shows that similar winds may have been blowing in our Galaxy until relatively recently. Such outflows have been recorded in other galaxies.

Massive celestial objects like Fermi bubbles are enormous gamma-ray emitting regions extending either side of our Galaxy’s center over approximately 50,000 light years. They poke out from the plane of the Galaxy like balloons. Despite their mind-blowing scale, the mechanism by which they are formed is yet to be deciphered.

Now, Tokyo Metropolitan University’s Professor Yutaka Fujita has provided theoretical support for how such items might have come into being. Since its discovery, various theories have been advanced regarding how the Fermi bubbles were created, including the central supermassive black hole’s explosive activity, the black hole’s winds, and sustained star formation activity. It is difficult to distinguish between these scenarios. Still, the Suzaku satellite’s access to cutting-edge X-ray observations allows us to compare measurements to what we anticipate from other scenarios.

The simulations of Professor Fujita considered fast outflowing winds from the black hole injecting the necessary energy into the gas surrounding the center of the Galaxy. Comparing with the measured profiles, they found a good chance that the Fermi bubbles are produced by the fast outflowing winds, blowing at 1000km per second over 10 million years. These are not winds as we would experience them on Earth, but streams of highly charged particles traveling at high speeds and propagating through space.

Professor Fujita’s calculations included fast outflowing winds from the black hole that would provide the requisite energy to the gas encircling the Galaxy’s center. They concluded that there was a good possibility that the fast outflowing winds, blowing at 1000 kilometers per second over 10 million years, caused the Fermi bubbles by producing comparisons with the measured profiles. These are streams of highly charged particles moving quickly through space, not winds, as we would experience them on Earth.

Prof. Fujita said“The winds predicted by the simulation are similar to outflows observed in other galaxies. The correspondence suggests the same massive outflows seen in other parts of the universe were present in our Galaxy until fairly recently.”

Journal Reference:

  1. Yutaka Fujita. Evidence for powerful winds and the associated reverse shock as the origin of the Fermi bubbles. Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stac3312
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