A star is torn - and it doesn't happen all that often
A computer simulation shows what it would look like if you were near a black hole looking towards a galaxy like the Milky Way. Photo: Ute Kraus
WHEN a star is torn apart it's a rare event, happening only once every 10,000 years per galaxy. The odds of the light show also being captured by telescope or analysed by astronomers are slim.
So there was some excitement when an international group of astronomers reviewing observations taken in 2006 realised just what they were looking at.
The team, including Sydney University astrophysicist Sean Farrell, spent three years reviewing archival footage taken by the European Space Agency's X-ray telescope in the hope of spotting a rare event or object.
They found it in the form of a bright flare - a sign of a star being ripped apart by a supermassive black hole - in a galaxy some 500 million light years away.
The stray star was observed again in 2007 at increased brightness, according to the study's leader, Dacheng Lin.
But by February this year, when the team searched for it using a NASA X-ray telescope, they could find no trace of the star, which had been obliterated by a supermassive black hole.
''We've been pretty lucky,'' Dr Farrell said. ''We had indeed stumbled on to a very rare extreme event … we were very lucky that the telescope happened to have this event in its field of view.''
Dr Farrell said the star had strayed too close to the black hole's narrow boundary, and astronomers were able to establish its destruction because of the swirling debris which emitted X-rays picked up by the telescopes. Because X-rays do not penetrate Earth's atmosphere, the telescopes are located in space.
From the X-rays astronomers can also effectively take the temperature of the black hole, which reveals its mass.
The find, reported in the upcoming edition of Astrophysics Journal, is notable for the rarity of the event and for the information that scientists hope to glean from it.
Supermassive black holes exist in the middle of galaxies and have three traits - mass, spin and charge. Learning more about their characteristics could also test and refine Albert Einstein's theories. Relatively little is known about supermassive black holes, although they have the potential to reveal a great deal about the formation of galaxies.
''This is very important as their influence on galaxies has an enormous effect on gas, stars, planets and, of course, life itself," Dr Farrell said.
"By studying the boundaries of black holes we can gain crucial knowledge about these extreme objects and their impact in the universe."