To study the origins of our universe is to struggle with profound chicken-or-egg questions. We know the Big Bang happened. Cosmologists can see its afterglow in the sky. But no one knows whether the laws of physics or even time itself existed before that moment. Nor can we say exactly what happened next. The order in which certain celestial objects formed during the very early universe is hotly contested.
For a long time after the Big Bang, not much of anything could form. All of space was permeated by a roiling plasma. It was too hot and chaotic for any structure to cohere. Hundreds of thousands of years passed before a tiny hydrogen atom could even hold itself together. Another 100 million years or so after that, great clouds of hydrogen condensed and stars flared into being. Most cosmologists believe that these stars were the first large, free-floating structures to illuminate our universe, and that black holes appeared later. But some have proposed that it went the other way around.
In the deep sky, beyond the most ancient fully formed galaxies, astronomers have now found a mysterious and colossal object that may be a primordial black hole. Earlier this month, a team of them posted an analysis of the object based on observations made by the James Webb Space Telescope. If their account holds up, the standard view of how the universe evolved will need serious revamping.
Long before black holes were ever glimpsed in reality, they were theoretical objects, products of the scientific imaginary. In 1783, the English natural philosopher John Michell proposed the existence of “dark stars,” objects of such concentrated mass that light cannot escape their gravity. Michell was reasoning from Newton’s laws. More than 100 years later, Karl Schwarzschild and Robert Oppenheimer brought his dark-star idea into alignment with Einstein’s theory of general relativity. They showed how an ultradense star could keep collapsing until space-time curved back on itself, sealing off its light in a black hole.
All of this work was done on chalkboards and in notebooks. Black holes would remain notional until 1972, when astronomers confirmed that they’d actually detected one. In the decades that followed, more of these exotic objects were found in every part of the sky. People have now seen small ones and big ones. They have picked up the tiny space-time ripples that emanate outward from two merging black holes. They have learned that most, if not all, galaxies have a black hole at their center. The supermassive one in the middle of the Milky Way shoots out jets of particles that expand into enormous bubbles. These bubbles appear to help regulate star formation and other cosmic processes here in the only galaxy known to host life.
Most of the black holes that astronomers have identified appear to be collapsed stars. But some theorists, including Stephen Hawking, have suggested that there might be other kinds in the universe. During inflation—an expansive process that theoretically took place just after the Big Bang—quantum fluctuations could have caused large parts of the cosmos to spontaneously buckle inward, forming black holes before any stars had yet appeared. But cosmologists have had trouble imagining the mechanisms that could generate such large fluctuations. If the mysterious object that the James Webb Space Telescope has found really is a primordial black hole, they will have to go back to their chalkboards and notebooks.
That we can even get a peek at something from the early universe is a technological miracle. The Webb telescope spotted this object way out in the dark realm beyond the last visible galaxies, where the only things that glow are likely proto-galaxies and other cosmic bits and bobs in various stages of formation. Even when black holes are close to us, they can be difficult to detect, because they trap light. To see a black hole, astronomers rely on the wrenching violence that it inflicts on nearby matter, which throws off sparks in the form of electromagnetic radiation. But if this object is a black hole too, then not much matter is surrounding it, so it isn’t throwing off so many sparks. (In cosmology terms, it’s nearly “naked.”) Most of what astronomers see in its vicinity is hydrogen and helium left over from the Big Bang—not what you’d expect from a black hole that had formed from a collapsed star.
We will need many more observations, and probably a larger space telescope, to know for sure whether it’s a primordial black hole. After all, our images of this object were taken from clear across the observable universe. They barely qualify as blurry snapshots, and the analysis of them hasn’t yet been peer-reviewed. Peter Coles, a theoretical cosmologist at Maynooth University in Ireland, has noted that the object might be some other kind of strange, celestial body instead. Other cosmologists suggested to me that it could be a black hole that formed directly from a gas cloud without having first become a star. It could be something else entirely. At the frontier edge of astronomy, tantalizing new observations have a tendency to be mirages.
We might learn that this one has been misinterpreted. We might find definitive proof that stars are older than black holes, just as cosmologists had long supposed. But even so, black holes would still retain some claim to ontological primacy, because they last so much longer. From their perspective, a star is just a transitory stage, a chrysalis. If the universe continues to expand as cosmologists predict, a day will come when star formation will cease altogether. Tens of trillions of years after that, the final stars will burn out. When that last stellar ember cools and darkens, the age of black holes will still be in its early days. Black holes will exist far, far longer than the entire illuminated age of stars. Of all the forms that this cosmos assumes, they will be among the most enduring. In a deep sense, this universe is theirs.
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