The biggest explosion ever observed in the universe

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About eight billion years ago, a large cloud of hydrogen fell into a supermassive black hole, triggering the most energetic explosion ever observed by astronomers. The radiation burst was ten times more powerful than any known supernova and lasted for over three years, scientists led by Philip Wiseman of the British University of Southampton wrote in the “Monthly Notices of the Royal Astronomical Society.”

At first, astronomers could not make sense of the unusual cosmic event. Only observations with many different instruments, from the long-wave infrared range to high-energy X-rays, helped them find an explanation. The explosion could not be seen with the naked eye.

Discovered by special telescope

Explosions are not uncommon in the universe: from thermonuclear explosions in dying stars to supernovae that shatter all stars, to bursts of radiation that occur when supermassive black holes swallow entire stars. The range of such events is rich. But none of them matched the particularly energetic celestial event cataloged under the name AT2021lwx.

The explosion was first discovered in 2020 by the “Zwicky Transient Facility”, a special telescope at the Mount Palomar Observatory in the USA. With this, astronomers automatically look for transient events in the sky, such as starbursts. “So we came across it by chance,” Wiseman said in a statement from her university. The automatic telescope noticed the event and sounded the alarm.

six billion after the big bang

At first, researchers thought it was a supernova, or a star falling into a black hole. Other observations showed that the explosion occurred in a galaxy far, far away. It took eight billion years for the light to reach Earth from there—so the explosion took place eight billion years ago, about six billion years after the Big Bang.

The long distance also means that the blast was unusually powerful and lasted unusually long. “Usually, such eruptions last for several months, after which the radiation level drops,” Wiseman said. “It’s very unusual for something to shine so brightly for more than two years.”

The only objects in the universe with a luminosity comparable to AT2021lwx are quasars, supermassive black holes at the centers of distant galaxies. They emit radiation because matter is constantly falling into them from the outside and is heated in the process. “But such quasars flicker, their brightness fluctuates very strongly,” said Mark Sullivan, a colleague of Wiseman at the University of Southampton.

Observed for three years

In contrast, the AT2021lwx’s brightness first increased 100 times in about a hundred days and has been decreasing very slowly since then. Researchers searched old data for further explosions of the object – without success.

To find the cause of the explosion, Wiseman, Sullivan and their colleagues observed the celestial body for three years using a variety of instruments. With the data thus obtained, a scenario eventually emerged as the most likely explanation for the explosion: a large molecular hydrogen cloud likely fell into a black hole with a mass about a billion times our sun. The cloud was swallowed not all at once, but piece by piece – which triggered shock waves in the rest of the cloud, thus giving rise to powerful radiation.

Astronomers hope to find many more similar events with the next generation of automatic telescopes. “Because such eruptions are so rare,” Wiseman says. “But they are so energetic that they could play an important role in the evolution of the centers of galaxies.”

(SDA)

Source : Blick