TIGHTEST BLACK HOLE BINARY SYSTEM TO DATE DISCOVERED

 Astronomers at Rochester Institute of Technology and the University of New Mexico have discovered what could be the closest pair of supermassive black holes yet, orbiting each other only a light-year apart.
 Located in the active galaxy of Mrk 533, observations by the scientists revealed a double radio source in the centre of the galaxy. If confirmed, this would mean that the supermassive black holes would have a combined mass of 400 million Suns. The closest pair of black holes known until now, discovered in the galaxy 0402+379, orbit each other 24 light-years apart.
 Although these black holes remain only as candidates, there are some factors that favour the double black hole scenario. For example, Mrk 533's stubby radio-emitting jets have a strange Z shape. “This morphology is thought to result from the combined effects of the galaxy merger followed by the formation of the massive binary,” says study coauthor David Merritt of Rochester Institute of Technology.
 Large galaxies are thought to increase in size by merging with other galaxies. Therefore, two merging galaxies would only naturally have two black holes, bound together in an inward-spiralling orbit. However such pairs - especially the tight-knit ones - have been surprisingly hard to find.
Read more about this fascinating story at: http://www.skyandtelescope.com/astronomy-news/supermassive-black-holes-discovered-closest-tango-yet/
Image: Mrk 533 via NASA/ESA/Hubble