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A team of astronomers has discovered what is the most dramatic “switching on” of a black hole that they have ever seen.
J221951-484240, or J221951 in short, is one of the most luminous transient events ever observed in space, according to the Royal Astronomical Society. Transient events are objects in space that change their brightness over a short period of time. This particular one was discovered by researchers looking for electromagnetic light from a gravitational event.
They were using the ultraviolet and Optical telescope on the Neil Gehrels Swift Observatory to search for a kilonova. A kilonova is a sign of a neutron star merging with another neutron star or a black. They typically appear blue before fading and turning redder in colour over a period of days. But J221951 was different—it did appear blue in the beginning but did not change colour or fade rapidly as a kilonova should.
The researchers then examined the light spectrum of the cosmic object using observations from the Hubble Space Telescope and were able to determine that it was around 10 billion light years away. The gravitational wave signal they were looking for was detected less than 500 million light-years away. The fact that the object shone so brightly over such a large distance means that it is one of the most luminous transients ever detected.
Based on available evidence, the researchers conclude that the object is a result of a supermassive black hole feeding on the material around it very fast. Just before it was detected, a red galaxy was observed near it. The location of J221951 corresponds with the location of the galaxy’s centre, where a massive black hole should be.
The black hole had started to shine suddenly, about 10 months before its initial detection. This means that it suddenly started feeding quickly after being quiet for a long time.
“Our understanding of the different things that supermassive black holes can do has greatly expanded in recent years, with discoveries of stars being torn apart and accreting black holes with hugely variable luminosities. J221951 is one of the most extreme examples yet of a black hole taking us by surprise. Continued monitoring of J221951 to work out the total energy release might allow us to work out whether this is a tidal disruption of a star by a fast-spinning black hole, or a new kind of AGN switch on,” said Matt Nicholl, a member of the research team, in a press statement.
The study has been accepted for publication in Monthly Notices of the Royal Astronomical Society.
