When a massive star, 20 to 30 times the mass of our sun, ends its life in a brilliant burst of light, known as a supernova, the remaining core collapses in on itself due to gravity. The result is widely thought to be a cosmological phenomenon called a black hole — a deep well in the fabric of spacetime from which nothing escapes.
One of the most difficult challenges of studying this giant star collapse is recreating the point where it forms a black hole. They have been working on this for decades and are still sorting out the details. The latest paper on this topic, by lead author Laura Mersini-Houghton from the University of North Carolina at Chapel Hill and Harald Pfeiffer at the University of Toronto, took an unorthodox approach which led them to conclude that black holes do not exist.
If true, this paper could have been ground-breaking for the astrophysics community. But the physicists made one major misstep in their methods. Their critical error was not in their calculations but in their treatment of a quantum effect called Hawking radiation.
It was predicted in 1974 by Stephen Hawking (hence the name), who suggested that black holes don’t just suck everything in. Some particles escape as what is now called Hawking radiation, shown in the animation below as the red-white ring around a black hole.
Since then, scientists have gone on to show that Hawking radiation can, in fact, kill a black hole by shedding away its mass into space until there’s nothing left. Ethan Siegal explained this phenomenon in his Medium post “How will Black Holes die?“
If Hawking radiation evaporates mass into space for a black hole, why wouldn’t it do the same for a collapsing star before it becomes a black hole? This is the question that Mersini-Houghton and Pfeiffer asked themselves. But it was the wrong question, Dimitrios Psaltis, a professor of astronomy and physics at the University of Arizona, told Business Insider.
“If you do not assume the black hole is fully formed and you actually take the star and let it collapse into a black hole, what you typically find is that the quantum effects get so enhanced that they effectively generate such enormous pressure that it reverses collapse,” said Psaltis, who models core collapse and black hole formation for a living. “This is the premise of this work,” he said referring to Mersini-Houghton and Pfeiffer’s paper.
Mersini-Houghton and Pfeiffer got a kind of run-away Hawking radiation effect that instead of enabling core collapse, it reversed it. If the core does not collapse, and if it never collapses, it cannot form a black hole.
This is not the first time that scientists have attempted to incorporate Hawking radiation into their core collapse models, Psaltis said, and the handful of papers before this latest version have led to similar conclusions, essentially stating that black holes aren’t real.
The right way to model core collapse, Psaltis said, is to incorporate both the quantum effects of Hawking radiation and the gravitational effects predicted by Einstein’s Theory of General Relativity — something Mersini-Houghton and Pfeiffer did not do.
Although General Relativity does a great job predicting a black hole’s whacky gravitational effects, like light warping shown above, it does not predict quantum effects like Hawking radiation. Unifying the physics of these two theories is one of the biggest unsolved mysteries of this field and no theory of “quantum gravity” exists, yet, despite concerted efforts.
So, for physics as we know it right now: “This is an impossible calculation,” Psaltis said.
Therefore, scientists continue to chip away at the problem, building on each other’s models that usually model the collapse separately from the black hole. Unfortunately, for Mersini-Houghton and Pfeiffer, it doesn’t look like their model will be in this mix because of their unorthodox conclusions. But what if they’re right and black holes don’t actually exist?
Psaltis, Todd Thompson, a professor of astronomy at Ohio State University, and a number of other scientists agree that this is highly unlikely. The reason is in the observational evidence.
“We have abundant evidence that black holes — or something very much like them — exist,” Thompson told Business Insider. “This evidence comes from the orbits of stars around the supermassive black hole at the center of our galaxy.”
Astrophysicists strongly believe that these observations are compelling evidence for the existence of black holes.
Scientists are also investing in a project, called the Event Horizon Telescope, that will take the first ever picture of a supermassive black hole’s “shadow” — a phenomenon that all supermassive black holes should have because of the way they bend light around them, according Einstein’s Theory of General Relativity. Such an image would be direct evidence that black holes exist.
“I think that will put all questions to an end,” Psaltis said.
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