If there were ever sentient beings in the Ophiuchus cluster, a faraway conglomeration of galaxies in the southern sky, they are long gone. A few hundred million years ago, a mighty cosmic storm swept through that region of space. Hot gas suffuses the cluster, but the storm blew a crater through it more than a million light-years wide, leaving just a near-vacuum, a nattering haze of ultrahot electrical particles.
The culprit, astronomers suspect, was a gigantic outburst of energy from a supermassive black hole — the biggest explosion ever documented in the universe, according to Simona Giacintucci, a radio astronomer at the Naval Research Laboratory and the leader of the research team.
In a statement issued by the lab on Feb. 27, Dr. Giacintucci compared the effects of the explosion to the eruption in 1980 that ripped the top from Mount St. Helens in Washington. Except that “you could fit 15 Milky Way galaxies in a row” into the crater punched out of the gas by this eruption, she said.
The latest radio observations of the galaxy cluster were described in a paper in the Astrophysical Journal.
The alleged outburst would rank as the biggest explosion yet discovered in the history of the universe: the energetic equivalent of one billion supernova explosions, unleashed in a torrent that probably lasted 100 million years. A hundred million years of bad space weather.
That is extreme, but it may not be the worst scenario. Ophiuchus is relatively close to Earth, only about 390 million light-years away. If astronomers look farther afield, they might see evidence of equally outlandish events, said Norbert Werner, an astronomer at Masaryk University in Brno in the Czech Republic and at Eotvos Lorand University in Budapest, whose observations with NASA’s orbiting Chandra X-ray Observatory helped lead to the discovery.
A black hole with several billion times the mass of the sun presumably squats at the center of the Ophiuchus cluster, in a galaxy known only by a number, WISEA J171227.81-232210.7.
Black holes are best known for their ability to swallow matter and energy, including light, and remove it from the universe forever. But they have another trait: They belch, and when a black hole belches, you don’t want to be anywhere nearby. Paradoxically, belching black holes are the brightest objects in the universe, producing the fireworks known as quasars and other violent phenomena.
Galaxy clusters are the largest conglomerations of matter in the universe, containing the equivalent of trillions of suns. But most of that matter is in the form of intergalactic gas so hot that it radiates X-rays, which astronomers use to spot clusters far out in space. When this gas cools and sinks to the center of the galaxy, it provides the fuel for outbursts by which a supermassive black hole can affect realms of the cosmos far beyond the originating galaxy.
On the way to disappearing, the gas swirls around the edge of the black hole like water around a drain. Pressures in this doughnut of doom squeeze powerful jets of particles and radiation out the top and bottom of the disk, fire-hosing the universe.
In 2003, observations with the Chandra satellite found that regular pulsations of a giant black hole in a galaxy in the Perseus cluster of galaxies were generating waves across intergalactic space with the frequency of a B-flat 57 octaves below middle C. The black hole was “singing.” By blowing periodic bubbles in the gas around it, the black hole was preventing stars from forming. Other singing black holes were subsequently found.
In 2016, a sharp discontinuity appeared in Chandra’s X-ray maps of the Ophiuchus cluster. Dr. Werner, then at Stanford, wondered if it represented the edge of another black hole bubble. He and his colleagues ultimately concluded that it was not, “because it would have to be the result of the most powerful outburst that we have ever seen in the universe,” he wrote in an email.
But Dr. Giacintucci and her colleagues persisted. They examined data from the European Space Agency’s XMM-Newton X-ray satellite, which also revealed an “edge,” and from a pair of radio telescopes: the Murchison Widefield Array in Australia and the Giant Metrewave Radio Telescope in India.
The radio telescopes clinched the case. The region lacking X-rays on the other side of the “edge” was full of radio noise, exactly as expected if a beam of powerful high-energy particles had blasted that region clean.
“The radio data fit inside the X-rays like a hand in a glove,” said Maxim Markevitch of NASA’s Goddard Space Flight Center in Greenbelt, Md., and a member of Dr. Giacintucci’s team.
Dr. Werner said that the black hole would have had to swallow about 270 million solar masses of material to have created such a big blast. The storm could have raged for 100 million years. It takes a long time to digest a small galaxy worth of suns.
It’s all over now. The pool of cool gas feeding the black hole is exhausted or has sloshed over to another part of the Ophiuchus cluster. But even bigger storms may yet be found.
“I’m glad that we were proven wrong by new evidence,” Dr. Werner said. “And I think that this result means that many more such large ‘craters’ are lurking in the universe. They are outside the well explored X-ray bright cluster cores, waiting for the next generation of instruments to discover them.”
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