When the Fermi Gamma-Ray Space Telescope entered low-Earth orbit in 2008, it opened our eyes to a whole new universe of high-energy radiation.
One of its most curious discoveries was the Fermi Bubbles: giant, symmetrical blobs extending above and below the galactic plane, 25,000 light-years on each side from the Milky Way’s center, glowing in gamma-ray light—the highest energy wavelength ranges on the electromagnetic spectrum.
Then, in 2020, an X-ray telescope named eROSITA found another surprise: even bigger bubbles extending over 45,000 light-years on each side of the galactic plane, this time emitting less energetic X-rays.
Scientists have since concluded that both sets of bubbles are probably the result of some sort of outburst or outbursts from the galactic center and the supermassive black hole therein.
Hypothesis Which Spells Out
A single hypothesis that explains both sets of bubbles in one fell swoop has now been developed by physicist Yutaka Fujita from Tokyo Metropolitan University in Japan using simulations.
He has discovered that the X-ray emission results from a strong, swift wind slamming into the flimsy gas filling interstellar space, creating a shock wave that echoes back through the plasma and causes it to radiate that intense glow.
Inactive Black Hole
Sagittarius A*, the supermassive black hole at the center of the Milky Way, is remarkably quiet for a black hole. It is categorized as “quiescent” due to its low feeding activity. But it hasn’t always been that way. And the area around an active black hole can be affected in a variety of ways.
Based on information from the now-retired Suzaku X-ray satellite, jointly run by NASA and the Japanese Space Agency, Fujita’s exploration of the Fermi bubbles was possible (JAXA). He employed numerical simulations to try to replicate Suzaku’s observations of the X-ray structures connected to the bubbles using black hole feeding mechanisms.
Easy To Distinguish Among Different Apparatus
In his study, he demonstrates that it is possible to discern between different energy-injection mechanisms using a combination of the density, temperature, and shock age profiles of the X-ray gas.
We find that the bubbles were produced by a fast wind from the galactic center by comparing the outcomes of numerical simulations with observations because it causes a significant reverse shock and replicates the temperature peak there.
He concluded that a black hole wind blowing at a speed of 1,000 km/s (621 miles) from a previous feeding event that lasted for around 10 million years and ended relatively recently is the most likely scenario.
Conundrum Of The Fermi Bubbles
The charged particles hit the interstellar medium as the wind spreads out, creating a shock wave that returns to the bubble. These backward shock waves heat the substance inside the bubbles, which makes it light.
The temperature profile of the X-ray structure was faithfully simulated by Fujita’s numerical calculations.
He looked into the likelihood of a single, powerful explosion coming from the galactic core but was unable to create Fermi bubbles. This shows that the mystery structures were most likely created by a gentle, constant wind coming from the galactic core.
The most likely origin of the mystery structures, according to this, was a slow, constant wind from the galactic center. In addition, star formation—another activity that generates cosmic winds—cannot be used to explain the strength of the wind; it is only due to Sagittarius A*.
In his study, he states that “the wind may be the same as active galactic nucleus outflows regularly detected in other galaxies and assumed to regulate the evolution of galaxies and their center black holes.”