News in Science

Monster black hole eats worlds

Cosmic cannibal A new study claims a supermassive black hole at the centre of our galaxy is ripping apart entire worlds on a daily basis.

The research by scientists led by Dr Kastytis Zubovas from the University of Leicester in the United Kingdom, explains why Sagittarius A, a giant black hole 26,000 light-years from Earth, flares up in spectacular daily displays of x-rays and infrared radiation.

Writing on the pre-press website ArXiv.org, Zubovas and colleagues propose Sagittarius A, which is 4,000,000 times the mass of the Sun, is destroying planets and asteroids that have formed in a torus of dust and gas around the black hole.

They claim these clouds are a mixture of primordial chemicals and the remains of stars that have already been shredded by the black hole.

That's a similar environment to the protoplanetary disks around stars in which planets form.

Black hole solar systems

This hypothesis has raised the possibility that planetary systems could be evolving around the Milky Way's central black hole in the same way that they would around a star.

Michele Bannister, a graduate student in planetary astronomy at the Australian National University's Mt Stromlo Observatory, says it is plausible that planets can form on the edge of a black hole.

"While the galactic centre is an incredibly energetic environment, planets are very resilient and so could form there," says Bannister.

She says the daily eruption of x-rays and infrared radiation provides clues about the numbers of asteroids, comets and planets likely to exist close to the galactic centre.

Planetary death

While this region may be conducive to the formation of planets and asteroids, Zubovas and colleagues point out that it's also an area where these bodies are destroyed as they move too close to the central black hole.

When this happens, a burst of x-rays and infrared radiation a hundred times greater than normal background energy is detected coming from Sagittarius A, they report.

But the radiation released as the planets and asteroids are destroyed is just a tiny fraction of the levels released when a star falls into the black hole, an event which is estimated to happen once every 100,000 years.

Associate Professor Alistair Graham from Melbourne's Swinburne University says scientitsts have only recently been able to understand how stars and planets can form in hostile environments near supermassive black holes.

"Most, if not all galaxies are thought to have supermassive black holes at their centres."

"The huge bursts of energy and particles beaming out from these gravity wells as stars are torn apart, couldn't explain the small scale x-ray and infrared flares seen daily from Sagittarius A", says Graham.

"However this energy output does match the levels expected from an in falling asteroid or planet."