Several telescopes were used to track J221951 and determine its nature, including NASA’s Swift/UVOT and Hubble Space Telescope
A team of astronomers led by researchers from the University of Birmingham, University College London and Queen’s University Belfast have discovered one of the most dramatic “ignitions” of a black hole ever seen. They will present their findings on Tuesday 4 July at the 2023 National Astronomy Meeting in Cardiff. The work will also be published in the Monthly Notices of the Royal Astronomical Society.
J221951-484240, known as J221951, is one of the most luminous transients (astrophysical objects that change their brightness in a short period of time) ever recorded. It was discovered by Dr Samantha Oates, an astronomer at the University of Birmingham, and her team in September 2019 while searching for electromagnetic light from a gravitational wave event. The team was using the Ultraviolet and Optical Telescope aboard the Neil Gehrels Swift Observatory to search for a kilonova, the sign of a neutron star merging with another neutron star or black hole. A kilonova usually appears blue, then fades and becomes redder over a time scale of days. What they found instead was something even more unusual: J221951. The transient appeared blue, but did not change color or fade rapidly as a kilonova would.
Several telescopes were used to track J221951 and determine its nature, including NASA’s Swift/UVOT and Hubble Space Telescope, the South African Large Telescope, and ESO facilities such as the Very Large Telescope and the GROND instrument on MPG/ESO 2.2-meter telescope at La Silla Observatory. A spectrum of J221951 taken with the Hubble Space Telescope ruled out the association of J221951 with the gravitational wave event. By examining the light spectrum of J221951, Dr. Oates and her team were able to determine that the source is about 10 billion light-years away, in contrast to the gravitational wave signal that was detected less than 500 million light-years away. light years away. The fact that it shines so brightly at such a great distance makes J221951 one of the most luminous transients ever detected.
Evidence suggests that J221951 arose as a result of a supermassive black hole feeding very rapidly on surrounding material. A red galaxy was observed at the location of J221951 prior to its detection, and the location of J221951 is consistent with the center of the galaxy, where a massive black hole would naturally reside. It began to brighten very suddenly, around 10 months before the initial detection, which means that the black hole began to feed very rapidly after being quiet for a while. The ultraviolet spectrum shows absorption characteristics consistent with material pushed outward by a large release of energy. This, combined with its great luminosity, makes this one of the most dramatic “ignitions” of a black hole ever seen.
The team has identified two possible mechanisms that could explain this extreme feeding from a supermassive black hole. The first is that it may have been caused by a tidal disruption event: the disruption of a star as it passes close to the supermassive black hole at the center of its galaxy. The second is that it may have been produced by an active galactic nucleus changing from inactive to active. J221951 would then be the signal that an inactive black hole at the center of the host galaxy has begun to feed on material from an accretion disk.
Dr Matt Nicholl, a team member from Queen’s University Belfast, said: “Our understanding of the different things supermassive black holes can do has expanded enormously in recent years, with discoveries of stars tearing apart and accumulating holes. blacks with enormous variable luminosities”. And he adds: “J221951 is one of the most extreme examples yet of a black hole taking us by surprise. Continued monitoring of J221951 to calculate the total release of energy could allow us to determine whether it is a tidal disruption of a star by a fast-spinning black hole, or a new type of AGN switch.”
Dr N. Paul Kuin, another member of the team from University College London’s Mullard Space Science Laboratory, said: “The key discovery was when Hubble’s ultraviolet spectrum ruled out a galactic origin. This shows how important it is to maintain a space-based UV spectrograph capability for the future.”