Thursday, February 22

How to create a black hole from nothing

How many ways are there to leave this universe?

Perhaps the best-known exit involves the death of a star. In 1939, physicist J. Robert Oppenheimer and his student Harlan Snyder, of the University of California, Berkeley, predicted that when a sufficiently massive star runs out of thermonuclear fuel, it collapses inward and continues to collapse forever, shrinking space , time and the Earth. light around itself in what we now call a black hole.

But it turns out that a dead star may not be necessary to create a black hole. Instead, at least in the early universe, giant clouds of primordial gas could have collapsed directly into black holes, avoiding millions of years spent in stardom.

This is the provisional conclusion recently reached by a group of astronomers studying UHZ-1, a speck of light dating back to not long after the Big Bang. In fact, UHZ-1 is (or was) a powerful quasar that spewed fire and X-rays from a monstrous black hole 13.2 billion years ago, when the universe was not yet 500 million years old.

This is unusually early, from a cosmic perspective, for such a massive black hole to have come into existence through stellar collapses and mergers. Priyamvada Natarajan, a Yale astronomer and lead author of a paper published in the Astrophysical Journal Letters, and her colleagues claim to have discovered a new celestial species in UHZ-1, which they call a supramassive black hole galaxy, or OBG. Essentially, an OBG is a young galaxy anchored by a black hole that has grown too big, too fast.

The discovery of this early quasar could help astronomers solve a related puzzle that has plagued them for decades. Almost every visible galaxy in the modern universe appears to host at its center a supermassive black hole millions of billions of times more massive than the Sun. Where did those monsters come from? Is it possible that ordinary black holes grew so large and so fast?

Dr. Natarajan and her colleagues propose that UHZ-1, and so perhaps many supermassive black holes, originated as primordial clouds. These clouds may have collapsed into early heavy nuclei sufficient to jump-start the growth of supramassive black hole galaxies. They are another reminder that the universe we see is governed by the invisible geometry of darkness.

“As the first OBG candidate, UHZ-1 provides compelling evidence for the formation of heavy initial seeds by direct collapse in the early universe,” Dr. Natarajan and her colleagues wrote. In an email, she added: “Nature appears to produce BH seeds in many ways beyond simple stellar death!”

Daniel Holz, a theorist at the University of Chicago who studies black holes, said: “Priya has found an extremely exciting black hole, if it were real.”

He added: “It’s just too big, too soon. It’s like looking into a kindergarten classroom and out of all the 5 year olds there is one who weighs 150 pounds and/or is six feet tall.

According to the story astronomers tell themselves about the evolution of the universe, the first stars condensed from clouds of hydrogen and helium left over from the Big Bang. They burned hot and fast, rapidly exploding and collapsing into black holes 10 to 100 times more massive than the sun.

Over the eons, successive generations of stars formed from the ashes of previous stars, enriching the chemistry of the cosmos. And the black holes left over from their deaths continued to merge and grow somehow, into supermassive black holes at the centers of galaxies.

The James Webb Space Telescope, launched two years ago this Christmas, was designed to test this idea. It has the largest mirror in space, 21 feet in diameter. More importantly, it was designed to record infrared wavelengths coming from the light of the most distant and therefore oldest stars in the universe.

But as the new telescope was pointed skyward, it spotted new galaxies so massive and bright that they defied cosmologists’ expectations. For the past two years, there has been debate about whether these observations actually threaten a long-standing model of the cosmos. The model describes the universe as composed of a trace amount of visible matter, surprising amounts of “dark matter,” which provides the gravity to hold galaxies together, and “dark energy,” which pushes these galaxies apart.

The discovery of UHZ-1 represents a turning point in these debates. In preparation for a future observation by the James Webb Space Telescope of a huge galaxy cluster in the constellation Sculptor, Dr. Natarajan’s team asked to spend time on NASA’s Chandra X-ray Observatory. The mass of the cluster acts like a gravitational lens, magnifying objects very far away in space and time. The researchers hoped to glimpse in the X-rays everything the lens might show.

What they found was a quasar powered by a supermassive black hole about 40 million times more massive than the Sun. Further observations by the Webb telescope confirmed that it was 13.2 billion light-years away. (The Sculptor cluster is about 3.5 billion light-years away.) It was the most distant and first quasar ever found in the universe.

“We needed Webb to find this extraordinarily distant galaxy, and Chandra to find its supermassive black hole,” Akos Bogdan of the Harvard & Smithsonian Center for Astrophysicals said in a press release. “We also took advantage of a cosmic magnifying glass that increased the amount of light detected.”

The results indicate that supermassive black holes already existed 470 million years after the Big Bang. That’s not enough time to allow the black holes created by the first generation of stars – which initially had 10 to 100 solar masses – to become so large.

Was there another way to create even bigger black holes? In 2017 Dr Natarajan suggested that the collapse of primordial gas clouds could have given rise to black holes more than 10,000 times more massive than the Sun.

“You can then imagine one of these later turning into this young, precociously large black hole,” Dr Holz said. As a result, he noted, “at every subsequent time in the history of the universe there will always be surprisingly large black holes.”

Dr Natarajan said: “The fact that these start life supermassively implies that they will likely eventually evolve into supermassive black holes.” But no one knows how it works. Black holes make up 10% of the mass of the first quasar UHZ-1, while they make up less than a thousandth of a percent of the mass of modern galaxies such as the giant Messier 87, whose black hole weighed 6.5 billion solar masses when its photo was taken by the Event Horizon Telescope in 2019.

This suggests that complicated environmental feedback effects dominate the growth and evolution of these galaxies and their black holes, causing their stars and gas to increase their mass.

“So, in fact, these extremely early OBGs are really telegraphing a lot more information and illuminating seed physics rather than later growth and evolution,” Dr. Natarajan said. He added: “Although they have important implications.”

Dr Holz said: “It would certainly be nice if it turned out to be what’s happening, but I’m sincerely agnostic.” He added: “It will be a fascinating story no matter how we solve the mystery of the first large black holes.”