A Voracious Black Hole at the Dawn of Time?


Astronomers claimed on Monday that they had discovered what might be the hungriest, most luminous object in the visible universe — a supermassive black hole that was swallowing a star a day. That would be the mass equivalent of 370 suns a year disappearing down a cosmic gullet 11 billion years ago at the dawn of time.

Burp indeed.

In a paper published in Nature Astronomy, Christian Wolf of the Australian National University and his colleagues from Australia and Europe, called the object at the center of a newly discovered quasar known as J0529-4351 “the fastest growing black hole in the universe.”

According to their estimates, this black hole tipped the scales as one of the most massive black holes ever found: 17 billion times as massive as the sun.

But other astrophysicists cast doubt on the result, questioning the methods by which the mass and luminosity of the new quasar had been estimated. They said the calculations were too uncertain to be conclusive. “They may have the right value, but I don’t think other observers would be shocked if it turned out the true mass was somewhat less,” said Daniel Holz, a theoretical astrophysicist at the University of Chicago.

“It does seem like an extreme object,” he said. But, he added, “I would be shocked if this turned out to be the most luminous quasar on the sky.”

Jenny Greene, a professor of astrophysical sciences at Princeton University, called the result “cute.”

“It’s nice to pick out the brightest of something,” she said.

Still, she agreed with Dr. Holz: “I don’t think this luminosity difference between this and other quasars is that big, and given the historical variability of quasars. It is not clear this object even really is more luminous than the others.”

Chung-Pei Ma, an astrophysicist at the University of California, Berkeley, weighed in, saying that estimate of these black hole masses could be off by a factor of two or three, “too large to make me lose sleep over the viability of prevailing cosmological models.”

This is a story of mind-bending big numbers, no matter how it comes out.

“There’s this weird game we play in astronomy where we’re always looking for the biggest, the brightest, the youngest, the oldest, etc.,” Dr. Holz said in an email. “Record-breaking objects are an efficient way to learn about the universe. Extremes help illuminate the contours of a problem, and help push our theories up to (or past) their breaking points.”

So it is with quasars and black holes. Quasars are distant objects that look like stars in the sky. In the 1960s, they were discovered to be emitting improbable torrents of energy, outshining all the stars in the galaxy in which they were embedded.

Astronomers have since concluded that all this energy is produced by matter falling into giant black holes. Just as a bathtub can’t drain in an instant, matter can only disappear down the cosmic drain at a rate, called the Eddington limit, depending on the black hole’s size. The rest is trapped in a sort of turnstile of doom, a swirling, sparking disc radiating energy. Which makes black holes, despite their name, the brightest objects in the universe.

Because they look like stars, quasars are hard to find in the sky. Dr. Wolf, a dedicated quasar hunter, said in an email that he relished the hunt. “It makes me feel like a kid again,” he wrote.

In this case, the quasar was hiding in plain sight in the database of the European Space Agency’s Gaia spacecraft, which has mapped the locations and properties of billions of stars since it was launched in 2013.

Dr. Wolf and his team identified it as a quasar after observing it with a telescope at Siding Spring Observatory in Australia. Follow-up spectrographic measurements with the Very Large Telescope operated by the European Southern Observatory at Paranal in Chile, allowed them to estimate the size of the accretion disc and the speed of the gas within it.

That in turn let them conclude that the black hole was some 17 billion solar masses and was accreting mass as fast as it could, at the Eddington limit, given its size or mass.

“In this process its accretion disc alone releases a radiative energy that is equivalent to the output from between 365 and 640 trillion suns,” the astronomers wrote in their paper. They hope to do better soon with an upgraded version of new high-resolution instrument, called Gravity on the Very Large Telescope, and the upcoming Extremely Large Telescope now under construction in Chile.

Acknowledging that all estimates of these distant early universe black hole masses were indeed uncertain by a large margin, Dr. Wolf said that the new instruments should be able to get a really well-defined image of the rotating storm disc leading to an accurate black hole mass. “This will check the scale that we are using right at the highest and most extreme end, and it may help to settle the debate on all these extrapolations that we currently rely on,” he said. “This will definitely be an important step for cosmology.”

By comparison, the black hole at the center of the Milky Way is only four million times as massive as the sun, and the black hole imaged at the center of the giant galaxy M87 in Virgo is 6.5 billion times as massive as the sun.

The recent detections of supermassive black holes residing in galaxies early in the history of the universe, only a billion or two years after the Big Bang, has spurred debate about how they could have grown so big so fast. Astronomers have long theorized that when the universe was only 100 million years old or so, it was seeded with black holes when the first stars burned out, exploded and collapsed into black holes a few dozen times the mass of the sun. In principle, in cosmic time, they could grow into the monsters found in the centers of almost all galaxies by merging with other black holes, accreting gas and eating the occasional star that wandered too close.

At its observed rate of growth, Dr. Wolf said, the quasar’s black hole would have doubled every 30 million years, which would have allowed the black hole’s mass to have grown to 17 billion suns within three billion years after the Big Bang.

But it was unlikely, he went on to say, that black holes actually grow at their maximum rates all the time. He noted that black holes only intermittently reach their Eddington limits, when a feast presents itself. Even more massive black holes have been discovered in the early times of the universe by telescopes like the James Webb Space Telescope, but none of them are as luminous as J0529-4351.

Which has led some astronomers to speculate that many of these black holes had primordial origins, predating stars and galaxies, and started out very massive.

“I am myself coming around to the idea that black holes formed before the galaxies did, and were the seeds around which galaxies formed rather than the other way around,” Dr. Wolf said.

“This has been proposed decades ago, but was considered too crazy to become mainstream,” he said. But the results from the new James Webb Space Telescope have breathed some life into this idea. “It is a very exciting time,” Dr. Wolf said.

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