Black holes can "snack" to obtain energy, but their food choices are very different from humans. An analysis published in Nature Astronomy on November 4 showed that when the black hole swallowed a star with a mass of at least 30 times that of the sun, people detected the brightest burst of light ever seen in a black hole - the peak brightness of this "fireworks show" was more than 10 trillion times brighter than sunlight.
The process of a black hole slowly devouring a star (artistic concept). Image source: Caltech
When astronomers first observed this object in 2018, they didn't realize it was a superflare. After noticing the object's increased brightness, researchers immediately targeted it with the 200-inch Hale Telescope at Mount Palomar Observatory in the United States. However, the results of the astroluminescence plots were disappointing. "It doesn't seem to be as interesting as we expected," said Matthew Graham, an astronomer at the California Institute of Technology and one of the authors of the paper.
In 2023, the research team noticed that even five years later, the flare was still unusually bright. Therefore, they used the Keck Observatory in Hawaii, USA, to conduct more in-depth observations. The results showed that the celestial body is about 3 million kiloparsecs, or 10 billion light-years, from the Earth. To appear so bright from such a long distance, the light it emits must be extremely dazzling. Astronomers now say the flare was 30 times brighter than any previously detected burst of light from a black hole.
Researchers analyzed several possible causes of the flare. Perhaps a supernova occurred near the black hole, or perhaps the flare was simply a trick of light - making it appear much brighter than it actually was due to the twisting effects of gravity. But the research team ultimately found that both explanations were inconsistent with the observations.
Researchers think a more reasonable explanation is that a massive star met its doom when it got too close to the black hole. When the black hole's gravity tears the star apart, the light it emits is dozens of times brighter than before. They also believe that because the flare has not completely disappeared, the star may not have been completely swallowed by the black hole.
As astronomers continue to watch the star's death, astronomer Joseph Michail of the Harvard-Smithsonian Center for Astrophysics wants to know whether the jets will gradually dim or explode again when light reaches the surrounding gas and dust. He also believes that future sky surveys may soon allow researchers to discover more similar phenomena. "These events are likely to become the norm," Michail said.
Graham believes that to fully understand these mysterious flare phenomena, astronomers will still need to continue observing the sky in the future. Because the black hole is so far away from the solar system that it would take about seven years on Earth to observe its two-year activity, which means astronomers can only witness the entire process of the black hole swallowing stars at 1/4 the speed. Graham admitted that "it will be a long journey" to fully observe more such events.
Related paper information: https://doi.org/10.1038/s41550-025-02699-0