A galaxy is a giant celestial body in which stars, white dwarfs, neutron stars, black holes, interstellar matter and dark matter are gathered by gravity. Astronomers predict that in about 5 billion years, our galaxy will collide with the neighboring Andromeda Galaxy 2.5 million light-years away.
What will happen if Andromeda collides with our galaxy, which is similar in size and about a third of the mass of our galaxy?
Previously, it was thought that intergalactic collisions would necessarily increase the activity of the massive black hole at the center of the galaxy.
Imagination of the gas falling off the galactic core. © 2021 Miki et al.
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However, a research team at the University of Tokyo in Japan recently performed accurate supercomputer simulations for various galactic collision scenarios, and found that some collisions could rather reduce the activity of the central black hole.
The reason is that head-on collisions of galaxies can remove the nucleus of galactic material, cutting off the fuel supply to black holes in the galaxy.
The study, published on the 25th of’Nature Astronomy’, is expected to broaden our understanding of the evolution of our galaxy.
“Galaxy Collision, Close to Cloud Combination”
When you think about massive phenomena such as galactic collisions, you can feel the impact of imagining some sort of cosmic catastrophe in which stars break, explode, and destroy on a massive scale.
In reality, however, galactic collisions could be closer to combining a pair of clouds. When clouds collide, larger clouds usually absorb smaller ones.
Image simulating two different scenarios with a dynamic model. The top shows galactic collisions with decreasing core activity, and the bottom shows galaxies collisions with increasing core activity. © 2021 Miki et al.
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Likewise, when a galaxy collides, it is unlikely that the stars in the galaxy will collide. Previously, it has been said that when galaxies collide, the consequences can be enormous.
Galaxies collide in several different ways. Sometimes smaller galaxies collide with the outer parts of larger galaxies, pass through or merge, and in either case, many stars are exchanged along the colliding path.
“Galactic collisions do not necessarily increase black hole activity”
However, galaxies may collide head-on. In this case, small galaxies could be torn by the overwhelming tidal forces of large galaxies. In this scenario, it turns out that very interesting things could happen within the galactic nucleus.
“There is a huge black hole (MBH) in the center of most galaxies,” said Yohei Miki, a researcher at the University of Tokyo, the first author of the paper. “Astronomers have been exploring galactic collisions for a long time. It has been estimated that it will supply fuel in the form of material in the nucleus.”
Various galaxies in the universe. © Kosmo
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According to this estimate, it has been thought that the fuel supply to the black hole significantly increases the activity of the black hole, so that we can observe it with ultraviolet and X-rays.
However, as a result of this study, there is sufficient evidence to believe that such a series of events is not necessarily happening, and that in fact sometimes the opposite phenomenon occurs.
“Our galaxy collides with numerous galaxies before”
The notion that galactic collision only increases the activity of a giant black hole seems logical, but the Mickey team wanted to test it. They constructed galaxy collision scenarios into highly detailed models and simulated them with supercomputers.
A paper published on the 25th of’Nature Astronomy’. © Springer Nature / Nature Astronomy
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The research team reaffirmed the results of simulations that under certain circumstances, small galaxies entering into larger galaxies can actually dislodge the material around the large black holes of large galaxies. Because I have confirmed new facts.
This result suggests that, unlike previous theories, galactic collisions can reduce the activity of giant black holes instead of increasing them.
“In this study, we calculated the dynamic evolution of a round, donut-shaped gaseous substance surrounding a giant black hole,” said Mickey. “If an incoming galaxy accelerates a round torus beyond a threshold determined by the properties of the giant black hole. If ordered, these gaseous substances can be released and the giant black hole could starve.”
It is not yet clear how long this suppression of activity on the giant black hole will last, but it is believed that such events could last as long as a million years. The team is convinced that our galaxy has previously collided with numerous smaller galaxies.
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