by Astronomers have discovered the oldest black hole ever observed, dating back more than 13bn years to the beginning of the universe.
The observations made by the James Webb space telescope (JWST) show that it is in the heart of a galaxy 440m years after the big bang. At about a million times the mass of the sun, it is surprisingly a baby black hole, which raises the question of how it grew so large so quickly.
Professor Roberto Maiolino, an astrophysicist at the University of Cambridge, who led the observations, said: “It’s a big surprise that it’s so massive. That was the most unexpected thing.”
The observations, published on the preprint website Arxiv, do not take a direct image, which cannot be seen because no light can escape its bite. But astronomers have found telltale signatures on its accretion disk, the halo of gas and dust that flows rapidly around the cosmic hole.
Astronomers believe the earliest black holes could help unravel the puzzle of how their gargantuan counterparts at the center of galaxies like the Milky Way grew to billions of times the mass of the sun. Until recently, they were thought to have been snowing for nearly 14bn years, growing steadily by merging and engulfing stars and other objects. But this snowball scenario cannot fully account for the epic proportions of today’s supermassive black holes.
The latest observations, of the galaxy known as GN-z11, put the origin of this mystery back to the beginning of black holes and suggest that they were born massively or very quickly.
“It’s always been a big problem to understand where black holes came from in the first place, but now that puzzle seems to be getting bigger,” said Professor Andrew Pontzen, a cosmologist at University College London. London, who was not involved in the research. “These results, using JWST’s power to peer back through time, suggest that some black holes instead grew at an amazing rate in the young Universe, much faster than we expected.”
One explanation, known as the heavy seed scenario, is that an early generation of black holes was born from the direct collapse of giant gas clouds, rather than from burnt stars collapsing under their own gravity at the end of their lives. Another possibility is that dense clusters of stars and black holes merged very quickly early in the universe.
The third hypothesis, which is more speculative, is that there are so-called primordial black holes that arose during cosmic inflation, the period of faster expansion than the lightening of the universe that occurred a fraction of a second after the Big bang.
This would flip on its head the assumed order of play, in which galaxies first form and then black holes begin to grow within them. Primordial black holes would effectively be woven into the fabric of the cosmos from the beginning.
“If that were true, it would have profound implications for the first fraction of a second of our Universe,” Pontzen said. “Either way, how black holes and galaxies grew together is an exciting story that we are only just beginning to piece together.”
The findings are the latest in a series of remarkable discoveries made by NASA’s space observatory just two years after its launch. JWST is about 100 times more sensitive than previous telescopes, such as Hubble, in detecting infrared light, the part of the spectrum used to see the most distant objects. “It’s basically like upgrading a Galileo telescope to a modern telescope. It is 400 years of discoveries that could have been compressed during the period of JWST operations,” said Maiolino.
He said before the telescope was launched that it had the potential to open a new window into “a boring expansion of what we know”. “That’s not what we’re seeing,” Maiolino said. “The world was quite generous. We’re really finding things we didn’t expect.”
What is a black hole?
Black holes are among the strangest and most ominous objects in the universe. Their gravity is so strong that neither matter nor light can escape their grip. A black hole’s threshold is traced through the event horizon, the point of no return. Anything that crosses this boundary is gone for good.
They are challenging to study because they are essentially invisible, but applying the laws of physics yields some curious insights. On the approach to a black hole, the gravitational gradient can be so extreme that objects are stretched out in a process called spaghettiization. At the event horizon, the gravity is so fierce that the light is bent in a perfect loop around the black hole, meaning that if you were standing there you would be able to see the back of your own head.
What lies beyond the event horizon is unknown. Einstein’s theory of general relativity suggests that the density of a black hole would become infinite at the center of the black hole, creating a gravitational singularity. This rupture would have no “where” or “when” in space-time and would sit outside the realm of the traditional laws of physics. But it is not clear whether such singularities really exist.
Black holes come in a range of sizes. Stellar black holes, formed from the remnants of massive stars, can be up to 20 times more massive than our sun. Supermassive black holes, such as Sagittarius A* in the center of the Milky Way, can have masses equal to millions or billions of suns and play a critical role in Galactic evolution.
Astronomers have made significant progress in observing black holes over the past decade, with the first image of a human calf captured by the Event Horizon telescope in 2019, and observations of cataclysmic black hole mergers via gravitational waves sent across spacetime to perceive. . The latest observations, and James Webb’s even longer goals, will begin to piece together the origins of these enigmatic objects.
