NASA visualization of the Milky Way’s Fermi bubbles. Credit: ESA/Gaia/DPAC
Evidence reveals robust outflowing winds liable for the “Fermi bubbles.”
A scientist from Tokyo Metropolitan University has proven that enormous gamma-ray emitting bubbles across the middle of our galaxy have been produced by fast-blowing outward winds and the related “reverse shock.” Numerical simulations efficiently reproduced the temperature profile noticed by an X-ray telescope. Such outflows have been noticed in different galaxies; this discovering suggests related winds might have been blowing in our personal galaxy till fairly lately.
The universe is filled with large celestial objects that are but to be defined. One of those is the “Fermi bubbles,” so-called as a result of they have been first found by the Fermi Gamma-ray Space Telescope in 2010. These bubbles are huge gamma-ray emitting areas that stretch both aspect of the middle of our galaxy over roughly 50,000 light-years, protruding out from the aircraft of the galaxy like balloons as proven within the determine. Despite their mind-blowing scale, the mechanism by which they’re fashioned is but to be deciphered.
Fast winds flowing out from the galactic middle creates a ahead shock and a reverse shock. The latter varieties the define of the Fermi bubbles. Credit: Tokyo Metropolitan University
Now, Professor Yutaka Fujita from Tokyo Metropolitan University has introduced theoretical proof demonstrating how such objects might have been fashioned. Since their discovery, many hypotheses have been put ahead concerning the formation of the Fermi bubbles, together with an explosive exercise of the central supermassive black hole, winds from the black hole, and steady star formation activity. Telling these scenarios apart is a challenging task, but the availability of state-of-the-art X-ray observations from the Suzaku satellite gives us a chance to compare measurements with what we expect from various 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 that there was 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. These winds travel outwards and interact with surrounding “halo gas,” causing a “reverse shock” that creates a characteristic temperature peak. The Fermi bubbles correspond to the volume on the inside of this reverse shock front. Importantly, simulations also showed that an instantaneous explosion at the center could not reproduce the profiles measured by the telescope, lending weight to a scenario based on steady winds generated by the central black hole.
The author notes that the winds predicted by the simulation are similar to outflows observed in other galaxies. The correspondence suggests the same kinds of massive outflows seen in other parts of the universe were present in our own galaxy until fairly recently.
Reference: “Evidence for powerful winds and the associated reverse shock as the origin of the Fermi bubbles” by Yutaka Fujita, 12 November 2022, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stac3312
This work was supported by JSPS KAKENHI Grants-in-Aid (Grant Numbers 20H00181, 22H00158, and 22H01268).
