The death of a star at the hands of a massive black hole in a galaxy 650 million light-years away surprised astronomers not only because it occurred outside the center of the galaxy, where massive black holes usually lurk, but also because it triggered two high-energy outbursts months after the star’s destruction.
When a star becomes caught in the gravitational grip of a huge black holetidal forces began to stretch and tear the star. Such events, called “tidal disruption events” or TDEs, are relatively common. They release a huge amount of energy when the star is torn apart and its remains form a debris disk around the black hole.
In this case, the optical flare of the TDE was spotted in 2024 by the Zwicky Transient Facility on the 48-inch Samuel Oschin Telescope at the Palomar Observatory in California. Constant monitoring of the TDE, designated AT 2024tvd, at radio wavelengths over the next 10 months by an array of telescopes has identified two separate radio flares – for some reason delayed by 80 and 194 days, respectively, after the start of the TDE.
But what is even more surprising is the location of the TDE: around 2,600 light years from the center of its host galaxy. Most TDEs take place at the center of a galaxy, where a supermassive black hole hides.
Only three were seen off-center.
“This is truly extraordinary,” Itai Sfaradi of the University of California, Berkeley, said in a statement. statement. “Never before have we seen such a bright radio emission from a black hole tearing a star apart, pushing it away from the center of a galaxy, and evolving so quickly. This is changing the way we think about black holes and their behavior.”
Sfaradi and his Berkeley colleague Raffaella Margutti led an international team to track the development of TDE using the Very large painting in New Mexico, the Allen Telescope Array in California and the Submillimeter Array in Hawaii, as well as the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and the Arcminute Microkelvin Imager Large Array (AMI-LA) at the Mullard Radio Astronomy Observatory at the University of Cambridge.
It was AMI-LA who played a key role in capturing the radio show’s surprisingly rapid development – rapid in the sense that its energy grew and changed rapidly. These radio waves are produced when a flow of matter hits the gas surrounding the black hole. This gas could be the ordinary interstellar medium or debris from the destroyed star.
Why these releases were so delayed after TDE remains a mystery. The first radio flare was also accompanied by a detected
The second eruption is even more confusing.
Either it was a jet of matter moving at half the speed of light which was launched 170 days after the TDE and took 24 days to reach the surrounding gas, or a jet traveling at almost the speed of light which was launched after 190 days. The connection between this second explosion and the first and whether it was produced by the accretion of the same material remains unclear.
As for the black hole, Sfaradi’s best guess is that it is an intermediate-mass black hole, that is, a black hole whose mass is between 1,000 and 100,000 times that of the black hole. mass of our sun. There are two ways he could have ended up outside the center of the galaxy. Either it participated in a triple black hole interaction at the center of its galaxy that saw it ejected, or it was once the central black hole of a smaller galaxy that collided and merged with a larger one, and the black hole now wanders like a violent rogue through its new galaxy, obliterating any hapless stars that get in its way.
The results were published on October 13 in Letters from the astrophysical journal.
