The Fermi bubbles are large structures that emit gamma rays. They are symmetrical about the Galactic Center (GC) and their creation is attributed to intensive energy injection into the GC.
In this study, a scientist from Tokyo Metropolitan University has shown that large bubbles emitting gamma rays around the center of our Milky Way galaxy were produced by fast-blowing winds and the associated “reverse shock.”
The scientist focused mainly on the unbalanced 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 discern the energy injection mechanisms.
Numerical simulations accurately reconstructed the temperature profile recorded by an X-ray telescope. This study shows that similar winds were blowing in our Milky Way until recently. Such outflows have been recorded in other galaxies.
Massive celestial objects such as Fermi bubbles are huge regions of gamma-ray emission that span about 50,000 light-years on either side of the center of our Milky Way galaxy. They stick out like balloons from the plane of the Milky Way. Despite their staggering scale, the mechanism by which they form has yet to be deciphered.
Now Professor Yutaka Fujita of Tokyo Metropolitan University has provided theoretical support for how such items might come about. Since its discovery, several theories have been advanced as to how the Fermi bubbles formed, including the explosive activity of the central supermassive black hole, the black hole’s winds, and the ongoing activity of star formation. It is difficult to distinguish between these scenarios. Still, the Suzaku satellite’s access to advanced X-ray observations allows us to compare readings to what we expect from other scenarios.
Professor Fujita’s simulations assumed fast outflowing winds from the black hole injected the necessary energy into the gas around the center of the Milky Way. Compared to the measured profiles, they found a good chance that the Fermi bubbles are produced by the fast outflowing winds, which blow at 1000 km per second for 10 million years. These are not winds as we would experience on Earth, but streams of highly charged particles moving at high speeds and propagating through space.
Professor Fujita’s calculations include fast outflowing winds from the black hole that would provide the required energy to the gas encircling the center of the Milky Way. They concluded that there was a good possibility that the fast outflowing winds, blowing at 1000 kilometers per second for 10 million years, caused the Fermi bubbles by making comparisons with the measured profiles. These are streams of highly charged particles moving rapidly through space, not winds, as we would experience on Earth.
Professor Fujita said: “The winds predicted by the simulation are similar to outflows seen in other galaxies. The correspondence suggests that the same massive outflows seen in other parts of the universe were also present in our Milky Way galaxy until recently.”
- Yutaka Fujita. Evidence for strong winds and associated reverse shock as the origin of the Fermi bubbles. Monthly communications from the Royal Astronomical Society. DOI: 10.1093/mnras/stac3312