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AsianScientist (Mar. 30, 2021) – Scientists in Japan have found that galactic collisions can sometimes starve their black holes of gases rather than fuel them, contrary to previous assumptions. Their findings are detailed in Nature Astronomy.
While the phrase ‘galactic collision’ may conjure up images of destruction on an epic scale, the process is much slower than you’d think. In reality, these collisions between galaxies take millions of years—and more accurately resemble a pair of clouds combining rather than a cosmic cataclysm.
Still, when galaxies collide, the consequences can be enormous. In head-on collisions, for instance, the overwhelming tidal forces of larger galaxies can completely shred and absorb the gases of their smaller counterparts.
Accordingly, scientists assumed that such head-on collisions fueled the massive black holes at the centers of the larger galaxies. The tremendous amount of light produced when these gases combine is what we humans detect as ultraviolet light and X-rays on Earth.
Interestingly, recent findings from the University of Tokyo (UTokyo) suggest that direct collisions may actually eject the gases surrounding black holes.
“For as long as astronomers have explored galactic collisions, it has been assumed that a collision would always provide fuel for an massive black holes in the form of matter within the nucleus,” said lead author Research Associate Dr. Miki Yohei from UTokyo. “However, we now have good reason to believe that this sequence of events is not inevitable and that in fact the exact opposite might sometimes be true.”
To test their hypothesis, Miki and his colleagues constructed highly detailed models of galactic collision scenarios on supercomputers. True enough, the team saw that in some scenarios, the smaller galaxy stripped away the gases surrounding the larger galaxy’s black hole—effectively starving it.
Their findings promise to shed light on the behavior of galaxies like the Milky Way, which experts say has collided with smaller ones in the past. Moving forward, Miki and his team hope to conduct more detailed simulations of the collisions over longer periods of time.
“We computed the dynamic evolution of the gaseous matter which surrounds the MBH in a torus, or donut, shape,” said Miki. “If the incoming galaxy accelerated this torus above a certain threshold determined by properties of the MBH, then the matter would be ejected and the MBH would be starved. These events can last in the region of a million years, though we are still unsure about how long the suppression of MBH activity may last.”
The article can be found at: Miki et al. (2021) Destruction of the Central Black Hole Gas Reservoir Through Head-on Galaxy Collisions.
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Source: University of Tokyo; Photo: Miki et al.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.
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