Milky Way's black hole may be devouring asteroids

The supermassive black hole at the heart of the Milky Way may be devouring asteroids on a daily basis, a new study based on findings by Nasa’s Chandra spacecraft has suggested.

The Chandra X-ray Observatory, named in honour of Indian physicist Subrahmanyan Chandrasekhar, has been detecting X-ray flares about once a day coming from our galaxy’s central black hole known as Sagittarius A* (Sgr A*)for several years. Now, researchers found that these flares may actually be caused by asteroids falling into the black hole’s maw.

“People have had doubts about whether asteroids could form at all in the harsh environment near a supermassive black hole,” said lead study author Kastytis Zubovas of University of Leicester in the UK.

“It’s exciting because our study suggests that a huge number of them are needed to produce these flares,” Zubovas was quoted as saying by SPACE.Com.

The researchers suggested that a cloud around Sgr A* contains trillions of asteroids and comets that the black hole stripped from their parent stars. Asteroids passing within 160 million km of the black hole — roughly the distance between the earth and the sun — are likely torn to pieces by Sgr A*’s gravity, they said.

These fragments would be vaporised by friction as they encounter the hot gas flowing onto the black hole, much as meteors are burned up by the gases in Earth’s atmosphere.

This vaporisation, they said, likely spawns the X-ray flares, which last for a few hours and range in brightness from a few times to nearly 100 times that of the black hole’s regular output. Sgr A* then swallows up what’s left of the close-flying asteroid, added the researchers who detailed their findings in in the Monthly Notices of the Royal Astronomical Society.

“An asteroid’s orbit can change if it ventures too close to a star or planet near Sgr A*,” said co-author Sergei Nayakshin, also of the University of Leicester. “If it’s thrown towards the black hole, it’s doomed.”

It would take an asteroid at least 10 km wide to generate the flares seen by Chandra, the researchers estimate. The black hole may also be consuming smaller space rocks, but the resulting flares would likely be too faint to observe. The new study is in rough agreement with previous modeling work, which has estimated that trillions of asteroids are likely to surround the Milky Way’s central black hole.

“As a reality check, we worked out that a few trillion asteroids should have been removed by the black hole over the 10-billion-year lifetime of the galaxy,” said co-author Sera Markoff of the University of Amsterdam in the Netherlands.

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