The reactor at the Takahama nuclear power plant, on the west coast of Japan, suffered a steam leak on the night of January 22, according to the plant's operator, Kansai Electric Power Company (Kepco).

"A small steam leak occurred in Unit 1 of the Takahama nuclear power plant on January 21 at approximately 23:25 (9:00 GMT) when an operator was carrying out a routine inspection in the turbine room of the first floor ," the company said.

"If this signal turns out to be a black hole, it would be a highly significant discovery and the first-ever radio detection of one inside a cluster," said Alessandro Paduano, lead author of the study and a former PhD student at Curtin University in Perth, Australia.