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January 28, 2022

Black hole shown to engulf asteroids

By Mo-Yu Zhou | February 22, 2012

According to a new study, asteroids could be falling into the supermassive black hole in the middle of our Milky Way. The study is significant because the findings suggest that a huge number of asteroids must be present around the black hole.
NASA's Chandra spacecraft has been detecting X-ray flares coming from Sagittarius A* (or Sgr A* for short) about once a day for several years. According to the study, the flares may be caused by the black hole swallowing up asteroids in its proximity.
Sgr A* is the black hole in the center of our galaxy, and due to the clearly hostile environment around a black hole, it has been doubted that asteroids could form nearby at all. However, the study, led by Kastytis Zubovas of the University of Leicester in the United Kingdom and published in the Monthly Notices of the Royal Astronomical Society, suggests that, in fact, large numbers of asteroids may be present around Sgr A*, as evidenced by the production of the flares.
In fact, it is likely that a cloud near Sgr A* could contain trillions of asteroids, as well as comets that were stripped from their parent stars by the black hole.
The distance between the Earth and the sun is roughly 100 million miles or 160 million kilometers. At this distance from Sgr A*, asteroids would get torn to pieces by the black hole's gravity. In addition, if an asteroid gets too close to a star or planet close to Sgr A*, its orbit could change, meaning that it could be thrown toward the black hole.
Then, as the asteroids come into contact with the hot gas flowing onto Sgr A*, the asteroid fragments would be vaporized by friction, just as meteors get burned up by gases in the Earth's atmosphere.
It is this vaporization that probably gives rise to the X-ray flares detected by Chandra. The flares last for a few hours and can range from a few times to nearly 100 times as bright as the black hole usually is. Then, whatever is left of the asteroid gets swallowed up by the black hole.
The flares seen around Sgr A* would have to be generated by asteroids at least six miles or 10 km, wide. Although the black hole is probably also munching up smaller asteroids, the flares that would appear as a result would be too faint to detect.
Previous modeling work has estimated that trillions of asteroids are likely to be found around Sgr A*. Findings from this study roughly agree with this conclusion. While a few trillion asteroids should have been swallowed up by the black hole over the 10-billion-year lifetime of the Milky Way, the majority of the total number of asteroids should remain untouched.
The results could also be an indication of planets that come too close to the black hole, rather than asteroids, which would result in even brighter flares. However, such events would be extremely rare, since asteroids are much more common than planets.
Nevertheless, it is likely that it has happened in the past: about 100 years ago, the X-ray flares of Sgr A* became brighter by a factor of a million. Unfortunately, this happened before telescopes were invented. It has been detected, however, by X-ray 'echoes' reflecting off clouds, according to the researchers.
The study provides exciting new evidence for the size, amount and proximity of asteroids around our galaxy's black hole, contrary to doubts regarding the existence of asteroids around Sgr A*.

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