Astronomers suggest dark energy could come from black holes – 02/26/2023 – Sidereal Messenger

An international group of researchers may have stumbled upon the key to deciphering what dark energy is. According to them, she could be in the black holes. But this is a complicated story and still full of uncertainties.

The whole thing started in 1998, when the study of distant supernovae indicated that the expansion of the cosmos, from about 5 billion years ago, reversed the sign: before it was slowing down, then it started to accelerate. We live today in a universe with accelerated expansion. What could be causing this acceleration? In the absence of an explanation, cosmologists have called this element “dark energy”. Apparently, this mysterious component gradually became dominant over time. According to our best estimates, it should account for 68% of all content in the Universe.

So the group led by Duncan Farrah, from the University of Hawaii (USA), carried out a study, published in the Astrophysical Journal, comparing the masses of supermassive black holes in closer elliptical galaxies to those of their equivalents in more distant ones, reflecting the situation of billions of years ago. “Because these galaxies are not expected to do much, their central black holes shouldn’t grow very large over time,” explains Farrah. In contrast, the researchers noticed that present-day black holes are much larger than their older counterparts.

And here comes the striking coincidence, highlighted in a second article, in the Astrophysical Journal Letters: black holes seem to be growing coupled with the Universe’s own expansion. Farrah’s group raises the possibility that this is no mere accident, and their calculations suggest that a zero association between one thing and another has a probability of less than 0.02%. More than that, the researchers suggest that the production of black holes over cosmic time would respond adequately to what is estimated to be the total amount of dark energy, according to our best data.

Their hypothesis: instead of being an energy dispersed equally throughout the cosmos, such dark energy would have as its source the black holes of the Universe, which would grow in quantity (and in mass) during the cosmic expansion and would be responsible for the inversion of sign in the acceleration as observed by astronomers. According to Kevin Croker, co-author of the two studies, it is possible to obtain the same cosmological result if the dark energy is distributed in a perfectly uniform way or if it is localized and concentrated in many small points – as would be the case with black holes.

The idea is intriguing to say the least. However, there is still a long way to go before conviction forms that this is the answer to the dark energy riddle. To begin with, it is necessary to be certain that there really is this cosmological growth in the mass of black holes. Then, see if models of the cosmos that attribute them to the role of dark energy really work. The fact is that, among so many purely theoretical explanatory hypotheses, this one comes with a possible observational element, which makes it very attractive.

This column is published on Mondays in Folha Corrida.

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