ISU Astrophysicist Projects Alternate End Of The Universe: 'Black Dwarf Supernova'
Most physicists believe after stars burn out, it's all over—cold, silent, dead. But new theoretical work from an Illinois State University astrophysicist hints, maybe not.
Matt Caplan, assistant professor of physics, projects the last hurrah could be a cosmic fireworks show, as stellar remnants known as "black dwarfs" explode in supernovae.
The known laws of physics suggest a “heat death,” where stars run out of the fuel they need to burn and the cosmic processes we know today cease.
“Eventually, that gas will be exhausted,” said Caplan. "Without fresh gas, new stars stop forming. And eventually, galaxies will very slowly evaporate over trillions of years."
That doesn’t mean the unimaginably far future will be boring, Caplan said.
“The basic idea is that heat death is still going to happen. But there is this very interesting window of opportunity that opens up in about 10^1100 years where massive black dwarf stars, which are going to be these cold dead remnants of stars today, might start spontaneously exploding in supernova,” he said.
Black dwarfs, Caplan explained, are the dim, frozen remains of white dwarfs that occur when smaller stars use up their energy and shrink to a portion of their original size.
“A star like our sun is not going to explode. It doesn't have enough mass to eventually explode in a supernova—that is a fate that is reserved for stars more than about 10 times the mass of the sun. Stars like our sun, they're going to burn the hydrogen in their core into helium. And as they come to exhaust that fuel, the core is going to contract, the outer layers are going to sort of puff up and be shed off after it.”
But Caplan said once that “white hot exposed core of a star” gutters out, something can still happen.
“The probability is very, very low for these reactions to happen, but they are not forbidden,” he said. “If you wait for 10^1000 years, what you're going to find is that a star—a white dwarf today that was made of carbon, oxygen, neon...these very light elements—will have through quantum tunneling produced a large amount of iron. And this is significant because it means that the star is losing the ability to support itself against gravity.”
When the star exceeds its own mass limit, Caplan said, it can undergo a very rapid gravitational collapse that is a trigger for a black dwarf explosion.
Not all black dwarfs are headed to this fate. And those that do explode won’t produce an awe-inspiring display, Caplan said. It’ll be too dark and the distance between objects will have grown too far.
“No black dwarf will even be capable of seeing the explosion of another black dwarf, it won't be possible for light to ever travel the distance between them due to the expansion of the universe,” he said.
Caplan issued a caveat.
“Everything that we predict about the far future of the universe depends on our understanding of physics today,” he said. “But small changes in our understanding of physics—new discoveries about the expansion of the universe, or new particle physics that we might discover—could fundamentally change all of these predictions”
Still, Caplan said, it’s fun to ask the big questions—even if we’ll never know the answers.
“Everything in the world is sad enough as it is,” he said. “It's kind of nice to be reassured once in a while that nothing we ever do can matter on long enough time scales, and eventually, everything will be done anyway.”
Listen to the full conversation:
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