Researchers spot rare luminous jet spewed by supermassive black hole
Flash caused by a dying star’s encounter with a black hole is among the brightest optical flare ever observed
MINNEAPOLIS / ST. PAUL (12/1/2022)—University of Minnesota Twin Cities Assistant Professor Michael Coughlin is co-leading a team that has discovered one of the brightest optical flares ever observed—dubbed AT2022cmc—caused by a dying star’s encounter with a supermassive black hole. The discovery may help researchers better understand the physics of supermassive black holes at the centers of galaxies.
The team’s findings are published in Nature, the world's leading multidisciplinary science journal.
When a dying star flies too close to a supermassive black hole, the star is violently ripped apart by the black hole’s gravitational tidal forces, captured into a spinning disk orbiting the black hole, and eventually consumed by the black hole. This is what astronomers call a tidal disruption event (TDE).
But in some extremely rare cases, the supermassive black hole launches “relativistic jets”—beams of matter traveling close to the speed of light—after destroying a star. Coughlin and his colleagues in the Department of Astronomy at the University of Maryland and NASA Goddard Space Flight Center, discovered one such case at the California Institute of Technology’s Zwicky Transient Facility (ZTF) survey in February 2022.
“The last time scientists discovered one of these jets was well over a decade ago,” said Coughlin, who is an assistant professor in the University of Minnesota Twin Cities School of Physics and Astronomy and co-lead on the project. “From the data we have, we can estimate that relativistic jets are launched in only 1 percent of these destructive events, making AT2022cmc an extremely rare occurrence. In fact, the luminous flash from the event is among the brightest ever observed.”
Before AT2022cmc, the only two previously known jetted TDEs were discovered through gamma-ray space missions, which detect the highest-energy forms of radiation produced by these jets. As the last such discovery was made in 2012, new methods were required to find more events of this nature. To help address that need, the researchers implemented a novel, “big picture” tactic to find AT2022cmc: ground-based optical surveys, or general maps of the sky without specific observational targets. Using ZTF, a wide-field sky survey taken by the Samuel Oschin Telescope in California, the team was able to identify and uniquely study the otherwise dormant-looking black hole.
"We developed an open-source data pipeline to store and mine important information from the ZTF survey and alert us about atypical events in real time,” explained Igor Andreoni, a postdoctoral associate in the University of Maryland Department of Astronomy. “The rapid analysis of ZTF data, the equivalent to a million pages of information every night, allowed us to quickly identify the TDE with relativistic jets and make follow-up observations that revealed an exceptionally high luminosity across the electromagnetic spectrum, from the X-rays to the millimeter and radio.”
Follow-up observations with many observatories confirmed that AT2022cmc was fading rapidly and the ESO Very Large Telescope revealed that AT2022cmc was at cosmological distance, 8.5 billion light years away.
Hubble Space Telescope optical/infrared images and radio observations from the Very Large Array pinpointed the location of AT2022cmc with extreme precision. The researchers believe that AT2022cmc was at the center of a galaxy that is not yet visible because the light from AT2022cmc outshone it, but future space observations with Hubble or James Webb Space Telescopes may unveil the galaxy when the transient eventually disappears.
It is still a mystery why some TDEs launch jets while others do not seem to. From their observations, the researchers concluded that the black holes in AT2022cmc and other similarly jetted TDEs are likely spinning rapidly so as to power the extremely luminous jets. This suggests that a rapid black hole spin may be one necessary ingredient for jet launching—an idea that brings researchers closer to understanding the physics of supermassive black holes at the centers of galaxies billions of light years away.
“Astronomy is changing rapidly,” Andreoni said. “More optical and infrared all-sky surveys are now active or will soon come online. Scientists can use AT2022cmc as a model for what to look for and find more disruptive events from distant black holes. This means that more than ever, big data mining is an important tool to advance our knowledge of the universe.”
The research was supported by the National Science Foundation (Grant Nos. PHY-2010970 425, OAC-2117997, 1106171 and AST-1440341), Wenner-Gren Foundation, Swedish Research Council (Reg. No. 427 2020-03330), European Research Council (Grant No. 759194 432 - USNAC), VILLUM FONDEN (Grant No. 19054), the Netherlands Organization for Scientific Research, Spanish National Research Project (RTI2018-098104-J-I00), NASA (Award No. No. 80GSFC17M0002), the Knut and Alice Wallenberg Foundation (Dnr KAW 2018.0067), Heising-Simons Foundation (Grant No. 12540303), European Union Seventh Framework Programme (Grant No. 312430) Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee and Lawrence Berkeley National Laboratories.
Read the full paper entitled, “A very luminous jet from the disruption of a star by a massive black hole,” on the Nature website.