The supermassive black hole at the centre of the Milky Way apparently devours asteroids on a regular basis. This is the conclusion of astronomers, including Sera Markoff of the University of Amsterdam (UvA), based on research using the American Chandra X-ray Observatory. Over the course of several years, the space telescope discovered a series of X-ray blasts with a frequency of approximately one a day from the black hole Sagittarius A* (abbreviated as Sgr A*, pronounced as Sagittarius A star). These blasts were also observed in infrared images by ESO’s Very Large Telescope in Chile, the European X-ray satellite XXM-Newton and the Keck telescope in Hawaii.

The X-ray bursts always last from half an hour to a couple of hours with a brightness that varies from several times to 100 times that of the black hole’s normal ‘output’. The disintegration and subsequent vaporisation of asteroids that orbit the black hole may solve the mystery of the origin of these blasts. ‘We think that the blasts from Sgr A* may be caused by the black hole “gorging” itself on asteroids, says Kastytis Zubovas of Leicester University (UK) and the main author of an article published in Monthly Notices of the Royal Astronomical Society.

The astronomers suggest that a cloud of hundreds of billions of asteroids and comets, pulled from their mother star, surrounds Sgr A*. Asteroids that pass the black hole at a distance of around 160 million kilometres - roughly the distance from the earth to the sun - are rent into pieces by the tidal forces of the black hole. The fragments then vaporise as they fall through the thin hot gas that flows toward Sgr A*, similar to a meteor falling into the earth’s atmosphere. An X-ray flash is produced and what remains of the asteroids is eventually devoured by the black hole.

Although Sgr A* consumes many more smaller asteroids, the authors believe that the blasts are caused by asteroids with a diameter of 20 km or greater. The results tally with estimates of the number of asteroids that must be present in the region. ‘As a “reality check”, we have calculated that the black hole must have devoured several trillion asteroids in the 10 billion years that the Milky Way has existed,’ explains co-author Sera Markoff (UvA). ‘Only a fraction of the total number has been swallowed so there is still an ample supply.’

Starting this week, Chandra will be used to make sustained observations of Sgr A* in order to collect new information on the frequency and brightness of the blasts and to test the model presented. According to Markoff, who is Co-PI of this project, we should see the same number of blasts in 2012 as in the last 12 years.