by From the expiration of clocks to the death of stars, everything seems destined to eventually come to a standstill. But there is one very, very big thing to which this doesn’t seem to apply at all. That is the universe itself, which is getting bigger and bigger.
According to our physical descriptions of how the cosmos should behave, that growth should slow down. Instead, measurements show it is accelerating, powered by a mysterious force known as dark energy. And it’s a dilly of one enormous pickle.
But there’s something in the universe that could explain this, some scientists argue: the huge, dense, growing concentrations of matter we call black holes.
“If black holes contain dark energy, they can attach to and grow with the expanding universe, accelerating its growth,” says astrophysicist Kevin Croker of Arizona State University. “We can’t get details on how this is happening, but we can see evidence that it is happening.”
We don’t know what it is, but calculations suggest that whatever is responsible for the accelerated expansion makes up an estimated 70 percent of the universe’s matter-energy distribution.
What we see as expansion today may not always have been consistent.
According to current theory, an early period of growth in the cosmos was the period of inflation. Just after the Big Bang, the universe went from nothing to something big in a split second. It then grew relatively slowly for a time, until about 5 billion years ago, when the expansion became dominated by dark energy.
Whatever caused the universe to initially inflate, slow down, and speed up had to overcome the extreme gravity contained in a cosmic sum of matter compressed into one place.
“If you ask yourself, ‘Where in the later universe do we see gravity as strong as at the beginning of the universe?’ the answer lies at the center of black holes,” explains physicist Gregory Tarlé of the University of Michigan.
“It’s possible that what happened during inflation plays out in reverse: the matter of a massive star becomes dark energy again during the gravitational collapse — like a small Big Bang played out in reverse.”
The idea that black holes might be involved in dark energy stems from a relatively recently proposed concept called cosmological coupling, a proposal that stems from attempts to resolve the strangeness of black holes with interpretations of general relativity.
According to the hypothesis, the extreme distortions of space associated with black holes are linked to the expansion of the universe. As the universe grows, so do black holes; and as black holes grow, so does the universe.
Last year, a team of researchers published a paper demonstrating the plausibility of cosmological coupling by studying the supermassive black holes at the centers of ‘dead’ galaxies. These are galaxies that have used up their fuel, both growing new stars and fueling the growth of the supermassive black hole.
Any growth evidenced by the black holes in these galaxies can therefore not be attributed to normal growth mechanisms, but to cosmological coupling. When the team discovered that there were indeed signs of growth, they felt their idea had been validated.
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In a new paper, Croker and his colleagues have explored the link between black holes and dark energy – not as the black hole grows, but as it is born. They used the Dark Energy Spectroscopic Instrument to study the rate of formation of black holes due to the collapse of the cores of massive stars at the end of their lives, much later in the life of the universe than when the supermassive black holes formed. expansion of the universe.
“The two phenomena were consistent with each other: as new black holes formed as massive stars died, the amount of dark energy in the universe increased appropriately,” said physicist Duncan Farrah of the University of Hawaii.
“This makes it more likely that black holes are the source of dark energy.”
According to the theory of cosmological coupling, black holes convert normal matter into dark energy. The team’s calculations not only reproduced an expansion rate for the universe that was consistent with current measurements, but also provide an explanation for another problem: we have failed to find all the normal matter that should be in the universe .
The rate at which black holes are formed produces a dark energy conversion rate consistent with the amount of normal matter missing.
The work conveniently provides solutions to several outstanding questions in one fell swoop – pushing it to the top of the pile for explanations for the mysterious force driving the universe apart.
“Essentially, the question of whether black holes are dark energy, linked to the universe they live in, is no longer just a theoretical question,” says Tarlé. “This is now an experimental question.”
The research has been published in the Journal of Cosmology and Astroparticle Physics.
