Unravel the mystery of the cause of the Milky Way’s giant bubble, from the central black hole energy eruption

Extending above and below the galactic disk are huge mysterious structures called Fermi bubbles, each 25,000 light-years in diameter. In the past, astronomers could not determine the origin of the bubbles. Now, the Tsinghua University team has used advanced computer simulations to confirm that there are two groups of giant bubbles in the Milky Way—the eRosita bubble and the Fermi bubble. The eruption of black hole energy proves that the galactic black hole was very active “not long ago”.

In 2010, astronomers discovered through the Fermi Gamma-ray Telescope that two giant gamma-ray bubbles extend from the center of the Milky Way, symmetrical up and down with the disk of the Milky Way as the center, called Fermi bubbles. At that time, the astronomical community was debating the cause of Fermi bubbles. One group believed that it was caused by the eruption of black hole energy, while the other group claimed that it was the galactic wind generated by the supernova explosion.

In 2019, after the extended ROentgen Survey with an Imaging Telescope Array (extended ROentgen Survey with an Imaging Telescope Array) was launched, two bubbles similar in shape to Fermi bubbles, but larger and symmetrical, called Yiro Theta Bubble.

In the Irosita and Fermi bubbles, high-energy electrons interact with low-energy light to generate gamma rays, and the high-energy particles and shock waves inside are still expanding outward at a speed of 1,500 kilometers per second, but no one knew the source of these electrons in the past , Are these bubbles the remnants of star formation? The remnants of the eruption of the supermassive black hole at the center of the Milky Way? Or did a mix of mechanisms produce them?

A multinational research team composed of Assistant Professor Yang Xiangyi from the Institute of Astronomy, Tsinghua University, and astronomers from the University of Michigan and the University of Wisconsin, entered the data from the Irosita Telescope into the computer for hydrodynamic simulations, and found the temperature and density of the gas related to the black hole jet. The changes are consistent. The inner circle of the bubble is gamma rays emitted by high-energy particles ejected by the black hole, and the outer circle is X-rays released by gas shock waves, which confirms that the giant bubble in the Milky Way is caused by the same black hole jet event.

Yang Xiangyi explained that when the black hole at the center of the Milky Way absorbs matter of 10,000 to 100,000 times the mass of the sun, only a small part is actually eaten into the area where even light cannot escape. The speed of the speed of light is ejected to both sides, that is, the jet stream. When these two plasma jets push the galactic gas outward, a huge bubble is formed, and the galactic disk is full of stars to generate resistance, so that the upward and downward symmetrical mushroom-shaped bubbles are formed.

The research not only gives us a better understanding of how supermassive black holes evolve and interact, but also means that although the Milky Way black hole is currently in a dormant period, it is more like a “sleeping lion” because it was only actively erupting millions of years ago.

The new paper is published in the journal Nature Astronomy.

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