A supermassive black hole is the largest type of black hole, with a mass hundreds of thousands, millions, or billions of times that of the Sun. Black holes are astronomical objects that have undergone gravitational collapse, resulting in spheroidal regions of space from which nothing, not even light, can escape. According to observations, almost every large galaxy has a supermassive black hole at its center.
Astronomers have discovered a bright optical flare caused by the collision of a dying star with a supermassive black hole. What happens when a dying star approaches a supermassive black hole too closely?
According to University of Maryland astronomer Igor Andreoni, several things happen. First, the star is violently ripped apart by the black hole’s gravitational tidal forces – similar to how the Moon pulls tides on Earth, but with greater strength. Then, fragments of the star are captured in a rapidly spinning disk orbiting the black hole. Finally, the black hole consumes what is left of the doomed star in the disk. Astronomers refer to this as a tidal disruption event (TDE).
However, in extremely rare cases, after destroying a star, the supermassive black hole launches “relativistic jets” – beams of matter traveling close to the speed of light. Andreoni, who is a postdoctoral associate in the Department of Astronomy at UMD and NASA Goddard Space Flight Center, discovered one such case with his team in the Zwicky Transient Facility (ZTF) survey in February 2022. After the group publicly announced the sighting, the event was named “AT2022cmc.” The team published its findings in the journal Nature.
Astronomy is changing rapidly. More optical and infrared all-sky surveys are now operational or will be soon. AT2022cmc can be used as a model for scientists to look for and find more disruptive events from distant black holes.
Michael Coughlin
“The last time scientists discovered one of these jets was well over a decade ago,” said Michael Coughlin, an assistant professor of astronomy at the University of Minnesota Twin Cities and co-lead on the project. “From the data we have, we can estimate that relativistic jets are launched in only 1% of these destructive events, making AT2022cmc an extremely rare occurrence. In fact, the luminous flash from the event is among the brightest ever observed.”
Prior to AT2022cmc, the only two previously known jetted TDEs were discovered via gamma-ray space missions, which detect the highest-energy forms of radiation produced by these jets. Because the last such discovery was made in 2012, new methods were required to find more events of this type. To address this need, Andreoni and his team used a novel “big picture” strategy 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 study the otherwise dormant-looking black hole.
“We created an open-source data pipeline to store and mine important information from the ZTF survey and to alert us in real time about atypical events,” Andreoni explained. “The rapid analysis of ZTF data, the equivalent of 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 X-rays to millimeter and radio,” the researchers write.
Follow-up observations with many observatories confirmed that AT2022cmc was rapidly fading, and the ESO Very Large Telescope revealed that AT2022cmc was 8.5 billion light years away at a cosmological distance.
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 unknown why some TDEs appear to launch jets while others do not. Andreoni and his colleagues deduced from their observations that the black holes in AT2022cmc and other similarly jetted TDEs are likely spinning rapidly in order to power the extremely luminous jets. This suggests that a rapid black hole spin is one of the requirements 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,” said Andreoni. “More optical and infrared all-sky surveys are now operational or will be soon. AT2022cmc can be used as a model for scientists to look for and find more disruptive events from distant black holes. This means that big data mining is now more important than ever in furthering our understanding of the universe.”
