A massive star was gradually torn apart and consumed by a black hole in a stunning event that scientists have likened to “making a snack for lunch”.
This intense encounter was observed by astronomers around the world, and the event was presented at the AAS conference in Phoenix, Arizona. The researchers described the star as “torn apart” because the black hole’s enormous gravity tore it apart and ate its matter piece by piece.
Associate Professor of Astrophysics Daniel Burley, from Liverpool John Morris University, is lead author of a paper in the Monthly Notices of the Royal Astronomical Society. He told the conference: “We have discovered what we believe is a black hole merging with a massive companion star, tearing it apart into a disk that feeds the black hole. It is a rare and amazing phenomenon.”
The destruction produced one of the most powerful cosmic events ever recorded. For a brief period, the energy released reached nearly 400 billion times that of Earth’s Sun, surpassing even the most powerful supernovae known to astronomers.
A black hole devours a massive star
Astronomers have previously observed that black holes appear to consume stars in events known as tidal disturbance events. However, researchers have never seen anything like this happen on such a large scale.
Anna Hu, an assistant professor of astronomy at Cornell University and co-author with Burley on the paper, identified the remarkable event shortly after its light reached Earth. Using the Zwicky Transit Facility at Palomar Observatory in California, she discovered the object, officially named AT2024wpp and nicknamed Whippet.
Researchers soon suspected that the phenomenon could be a fast luminous blue optical transient (LFBOT), a rare and poorly understood type of visible cosmic event associated with the destruction of stars. Within a day, observations by the Liverpool Telescope in the Canary Islands and NASA’s Swift satellite in space showed that the object exhibited the expected characteristics of a LFBOT. It looked very blue and was producing x-rays.
Distance measurements by co-authors R. Michael Rich of the University of California, Los Angeles and Yu-Jing Chen of the California Institute of Technology showed that the transient was releasing much more energy than a normal supernova. Combined with other observations, including its exceptionally high temperature, the measurements led researchers to conclude that they were witnessing a star being torn apart and swallowed by a black hole.
“Although we doubted what it was, it was exceptional,” Burley added. “This was several times more active than any similar event and more than any known explosion resulting from the collapse of a star.
“Not only do these events help us identify black holes, but they provide a new way to determine where black holes occur, how they form and grow, and the physics that explains how this happens,” Burley added.
The shock wave races through the surrounding gas
Additional studies of AT2024wpp indicate that the event generated a powerful shock wave that traveled outward through the surrounding dense gas at about one-fifth the speed of light. But after about half a year, the shock suddenly seemed to “go away.”
Material pulled from the star formed a disk around the black hole and became extremely hot as it moved inward. This process produced X-ray radiation as well as a strong “wind” of gas. The outflow collided with material released by the star before its destruction, generating the bright blue and ultraviolet light emission seen during the first few days, as well as the radio and millimeter signals detected by astronomers.
The researchers believe that the shock “fades” after reaching the outer limits of the bubble created by the gas that the stricken star previously expelled.
A strange signal appears from the aftermath
One puzzling feature remains. Observations from the Keck Observatory, Magellan Observatory, and the Very Large Telescope showed no identifiable chemical signatures during the first month after the explosion. As the event began to fade, faint signs of hydrogen and helium gas appeared.
Helium produced particularly unexpected evidence. It was moving along the line of sight at a speed of more than 6,000 kilometers per second, indicating that a dense structure may have survived the initial explosion and is now moving rapidly toward us.
The researchers speculate that the signal could come from a “stream” of material released from the star’s core as the black hole’s massive gravity was tearing it apart. The most speculative possibility is that the matter comes from a third member of the system that is blown away by fast winds of particles and X-rays generated by the black hole feeding.
