Powerful blasts of radiation from distant galaxies have revealed signs of an elusive medium-sized black hole, which may be a link between the small black holes that we have observed and the supermassive black holes that sit at the centres of galaxies. These medium-sized objects are notoriously hard to find because they don鈥檛 shine brightly like supermassive black holes and are too big for current gravitational-wave detectors to spot.
Rachel Webster at the University of Melbourne in Australia and her colleagues spotted this cosmic middleweight by examining archival data on about 2700 gamma-ray bursts, extraordinarily bright flashes of radiation thought to come from massive explosions in other galaxies. They searched this catalogue for evidence of gravitational lensing, which occurs when a massive, dense object stretches light around it.
The researchers found only one example of gravitational lensing, in which the light from the gamma-ray burst was warped by an object about 55,000 times as massive as the sun. An object that massive yet dim is probably a black hole 鈥� and if that is the case, it is far smaller than the smallest supermassive black hole we have ever seen and far larger than the largest 鈥渘ormal鈥� one.
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鈥淲e can鈥檛 be 100 per cent sure [that this is a black hole], but the other likely objects are either not compact enough or not common enough,鈥� says Webster. She and her colleagues estimated that if this object is a black hole, there is probably about one of a similar mass per 15 million billion cubic light years.
This object and others like it may be a link between small black holes and extremely large ones. 鈥淲e鈥檝e got these small black holes and we鈥檝e got these supermassive black holes, but in the middle was nothing,鈥� says James Paynter at the University of Melbourne, part of the research team. Studying these objects could help us figure out how supermassive black holes form, which is a major mystery in modern astrophysics.
Nature Astronomy
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