Caption The giant black hole at the centre of the Milky Way may be devouring asteroids, creating flares that can be observed from Earth around once a day. Nasa scientists detected X-ray flares from the supermassive black hole known as Sagittarius A* - the flares last a few hours, and can be 100 times brighter than the black hole's normal energy output.
The black hole is surrounded by a cloud of trillions of asteroids and comets, say the scientists - and asteroids passing within 100 million miles of Sagittarius A*, the distance between Earth and the sun, will be pulled in and vapourised.
'People have had doubts about whether asteroids could form at all in the harsh environment near a supermassive black hole,' said Kastytis Zubovas of the University of Leicester in the United Kingdom. 'Our study suggests that a huge number of them are needed to produce these flares.'
'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 toward the black hole, it’s doomed.'
The flares - which have also been detected in infrared by the European Southern Observatory's Very Large Telescope in Chile - are thought to be created by space rocks above twelve miles in diameter.
The black hole may also be 'eating' smaller rocks, but the flares would be more difficult to spot.
Asteroids passing too close to the black hole - a huge object with a mass estimated to be at least half a million Suns - would be vaporized by friction as they pass through the hot, thin gas flowing into Sgr A*, similar to a meteor heating up and glowing as it falls through Earth’s atmosphere.
A flare is produced as the asteroid is swallowed eventually by the black hole.
Zubovas and his colleagues suggest there is a cloud around Sgr A* containing trillions of asteroids and comets, stripped from their parent stars.
These results agree with theories of how many asteroids are likely to be in this region, assuming that the number around stars near Earth is similar to the number surrounding stars near the center of the Milky Way.
'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. 'Only a small fraction of the total would have been consumed, so the supply of asteroids would hardly be depleted.'
Planets thrown into orbits too close to Sgr A* also should be disrupted by tidal forces, although this would happen much less frequently than the disruption of asteroids, because planets are not as common.
Such a scenario may have been responsible for a previous X-ray brightening of Sgr A* by about a factor of a million about a century ago. While this event happened many decades before X-ray telescopes existed, Chandra and other X-ray missions have seen evidence of an X-ray 'light echo' reflecting off nearby clouds, providing a measure of the brightness and timing of the flare.
“This would be a sudden end to the planet’s life, a much more dramatic fate than the planets in our solar system ever will experience,”