The black hole at the centre of the galaxy, formally known as Sagittarius A*, fascinates scientists. 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. For the past 20 years, Stefan Gillessen, astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Munich, Germany, has been observing the black hole. “So far there were only two stars 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 super massive 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 gravitational forces observed in their vicinity. So-called super massive black holes are the largest type of black holes. Their mass equals hundreds of thousands to a billion times the mass of our sun. The centre of all galaxies is thought to contain super massive 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 to scientists as it should provide some new insights.
Reinhard Genzel leads the team of astronomers from the European Southern Observatory which has discovered the gas cloud about to collide with the black hole at the heart of our galaxy 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 we near the collision, the cloud is expected to get much hotter. It will also probably start to emit X-rays as a result of the interaction with the black hole. This event will provide astronomers and astrophysicists a unique opportunity to observe how a gas cloud behaves so close to one of the most mysterious objects in our universe.
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