Astronomers may have solved the mystery of bubbles dominating the Milky Way: ScienceAlert

Astronomers may have solved the mystery of bubbles dominating the Milky Way: ScienceAlert

Astronomers may have solved the mystery of bubbles dominating the Milky Way: ScienceAlert

When the Fermi Space Gamma-Ray Telescope entered low Earth orbit in 2008, it opened our eyes to a whole new universe of high-energy radiation.

One of his most curious discoveries was the Fermi Bubbles: giant, symmetrical blobs extending above and below the galactic plane, 25,000 light-years on either side of the center of the Milky Way. , shining in the light of gamma rays – the most energetic wavelength ranges on the electromagnetic spectrum.

Then, in 2020, an X-ray telescope named eROSITA found another surprise: even bigger bubbles extending 45,000 light-years on either side of the galactic plane, this time emitting less energetic X-rays.

Scientists have since concluded that both sets of bubbles are likely the result of some sort of explosion or explosions of the galactic center and the supermassive black hole therein. The mechanism producing the gamma and X-rays, however, has been a little more difficult to pin down.

Now, using simulations, physicist Yutaka Fujita of Tokyo Metropolitan University in Japan has come up with a unique explanation that accounts for both sets of bubbles in one fell swoop.

The X-ray emission, he found, is the product of a powerful, fast-moving wind battering through thin gas-filled interstellar space, producing a shock wave that reverberates through the plasma. , causing him to have this energetic glow.

The supermassive black hole that powers the heart of the Milky Way — Sagittarius A* — is pretty quiet when it comes to black holes. Its feeding activity is minimal; it is classified as “quiescent”. It has not always been so. And an active black hole can have all kinds of effects on the space around it.

As matter falls toward the black hole, it heats up and blazes with light. Some of the material is funneled along magnetic field lines outside the black hole, which act like a synchrotron to accelerate particles to near light speeds. These are launched as powerful jets of ionized plasma from the poles of the black hole, shooting out into space up to millions of light-years away.

Additionally, there are cosmic winds: streams of charged particles that are whipped up by matter orbiting the black hole that then explode out into space.

While Sagittarius A* may be calm now, that hasn’t necessarily always been the case. Take a good look, and relics of past activity, such as Fermi Bubbles, can be found lurking in space around the galactic plane. By studying these relics, we can understand when and how this activity took place.

Fujita’s foray into Fermi bubbles is based on data from the now-retired Suzaku X-ray satellite, jointly operated by NASA and the Japanese Space Agency (JAXA). He took Suzaku’s observations of X-ray structures associated with bubbles and ran numerical simulations to try to reproduce them based on black hole feeding processes.

Diagram showing the structures surrounding Fermi bubbles. (Y. Fujita, MNRAS2022)

“We show that a combination of density, temperature, and shock age profiles of X-ray gas can be used to distinguish mechanisms of energy injection,” he wrote in his paper.

“By comparing the results of the numerical simulations with the observations, we indicate that the bubbles were created by a fast wind coming from the galactic center because it generates a strong reverse shock and reproduces the observed temperature peak there.”

The most likely scenario, he found, is a black hole wind blowing at a speed of 1,000 kilometers per second (621 miles) from a past feeding event that was measured over 10 million years old and ended fairly recently. As the wind blows outward, the charged particles collide with the interstellar medium, producing a shock wave that bounces back into the bubble. These reverse shock waves heat the material inside the bubbles, causing it to glow.

Numerical simulations developed by Fujita accurately reproduced the temperature profile of the X-ray structure.

He also investigated the possibility of a single explosive eruption from the galactic center and was unable to reproduce the Fermi bubbles. This suggests that a slow, steady wind from the galactic center was the most likely ancestor of the mysterious structures. And the power of the wind can only be attributed to Sagittarius A*, not star formation – another phenomenon that produces cosmic winds.

“Thus,” he wrote in his paper, “the wind may be the same as the outflows of active galactic nuclei often observed in other galaxies and thought to regulate the growth of galaxies and their central black holes.”

The document was published in the Royal Astronomical Society Monthly Notices.

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