Tight system of black holes in a distant galaxy
Astronomers have discovered three closely orbiting supermassive black holes in a galaxy more than 4 billion light years away. This is the tightest trio of black holes known to date and is remarkable since most galaxies have just one black hole, usually with a mass between 1 million to 10 billion times that of the Sun, at their centre. The discovery suggests that such closely packed supermassive black holes are far more common than previously thought.
An international research team, including Hans-Rainer Klöckner from the Max Planck Institute for Radio Astronomy in Bonn, Germany, performed VLBI (Very Long Baseline Interferometry) observations with radio telescopes at a number of frequencies to discover the inner two black holes of the triple system. The VLBI technique combines the signals from large radio antennas separated by up to 10. 000 kilometres to see details 50 times finer than that possible with the Hubble Space Telescope. In this project the Effelsberg 100m radio telescope took part in European VLBI network (EVN) observations covering two radio frequencies.
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