Black hole to destroy cloud

  • Giant gas cloud about to enter black hole
  • The black hole is at the centre of our galaxy
  • Astronomers to watch it happen in 2013

THE BLACK HOLE AT THE CENTRE of the our galaxy, formally known as Sagittarius A* – pronounced Sagittarius A star – is about to unleash its destructive power. By mid-2013, a gas cloud is expected to pass in its vicinity at a distance of only 36 light-hours (equivalent to 40,000,000,000 km), which is extremely close in astronomical terms. The cloud will be ripped apart.

For the past 20 years, Stefan Gillessen, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Munich, Germany, has been studying the black hole. “So far there have been only two stars [we have seen] that came that close to Sagittarius A*”, he says. “They passed unharmed, but this time will be different: the gas cloud will be completely ripped apart by the tidal forces of the black hole.”

A black hole is what remains after a supermassive star dies. When the “fuel” of a star runs low, it will first swell and then collapse to a dense core. If this remnant core has more than three times the mass of our Sun, it will transform to a black hole.

Direct observations of such black holes are impossible because they are coal-black and do not emit light or matter. But astronomers can identify a black hole indirectly due to the affect it has on objects in its vicinity.

So-called supermassive black holes are the largest type. Their mass equals hundreds of thousands to a billion times the mass of our Sun. The centres of all galaxies are thought to contain supermassive black holes. But their origin is not fully understood and astrophysicists can only speculate as to what happens inside them. Hence the imminent collision is of great interest, as it should provide some new insights.

Reinhard Genzel (European Southern Observatory) leads the team of astronomers that discovered the cloud and studied its trajectory. According to their observations, its speed has nearly doubled in the last seven years, reaching more than 8 million km/h.

The cloud’s edges have already started to shred and it is expected to break up completely over the coming months. As it nears the collision, the cloud is expected to get much hotter and probably emit X-rays.

Adapted from information issued by the Max Planck Institute for Extraterrestrial Physics.

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