Astronomers pave way for black hole census

How many live at home, are practising Jedis, etc

Russian astronomers have begun work that will allow them to work out how many black holes there are in the Universe.

The research team at the Space Research Institute in Moscow is using the European Space Agency's (ESA) gamma ray observatory, Integral, to measure the X-ray and gamma ray background radiation that permeates the universe.

This gamma background glow is thought to be caused by tens of millions of active black holes spread throughout space. In the softer X-ray band, the radiation is almost entirely populated by Active Galactic Nuclei (AGN), the researchers say.

The team is using the Earth as a giant shield to block out those distant X-rays and gamma rays. As the recorded radiation dwindles, the astronomers can work out how much of it comes from nearby sources, and how much from the so-called background.

Described like this, the experiment seems simple enough, but Integral is not set up to record data in this way.

Its normal operation requires it to avoid pointing directly at Earth, as our planet is so bright it would blind the optical instruments used to determine the craft's altitude. So the researchers effectively had to fly the craft blind to get the measurements they were after.

The next step in this census is to build computer models that demonstrate how the emissions from the unseen black holes merge to create the background radiation. From this, the scientists will be able to predict the number and distribution of black holes throughout the universe. ®

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