Black holes account for no more than 40 per cent of dark matter, claim UCL scientists

Statistical analysis of 740 of the brightest supernovas discovered since 2014 suggests scientists will need to look elsewhere for dark matter

Black holes can't account for more than 40 per cent of the universe's 'dark matter'.

The finding, by researchers at the University of California, Berkeley, means that scientists will have to continue the search for the hypothetical form of matter, which supposedly makes up 84.5 per cent of all the matter in the universe.

The belief had been that black holes, which have such a compact mass that they can deform space-time - would account for almost all the dark matter in the universe.

Dark matter is one of astronomy's biggest conundrums. Despite comprising 84.5 per cent of all the matter in the universe, no one can find it. Proposed dark matter candidates span almost 90 orders of magnitude in mass, from ultra-light particles like axions to compact halo objects, or "MACHOs".

The scientists' experiments were conducted after they detected gravitational waves emitting from colliding black holes in 2015.

Despite comprising 84.5 per cent of the matter in the universe, no one can find it

However, after a statistical analysis of 740 of the brightest supernovas discovered since 2014, the physicists claim that none of them appeared to be magnified or brightened by hidden black hole "gravitational lenses" as first hoped.

The researchers, therefore, concluded that primordial black holes can make up no more than about 40 per cent of the dark matter in the universe.

They also said that they could have only been created within the first milliseconds after the Big Bang as regions of the universe with concentrated mass tens or hundreds of times that of the sun collapsed into objects a hundred kilometres across.

The results suggest that none of the universe's dark matter consists of heavy black holes, or any similar object, including MACHOs.

Several theorists have proposed scenarios in which there are multiple types of dark matter. But if dark matter consists of several unrelated components, each would require a different explanation for its origin, which makes the models very complex.

"I can imagine it being two types of black holes, very heavy and very light ones, or black holes and new particles," explained lead author of the study, Miguel Zumalacárregui.

"But in that case one of the components is orders of magnitude heavier than the other, and they need to be produced in comparable abundance.

"We would be going from something astrophysical to something that is truly microscopic, perhaps even the lightest thing in the universe, and that would be very difficult to explain."

An as-yet unpublished re-analysis by the same team using an updated list of 1,048 supernovas cuts the limit in half, to a maximum of about 23 per cent, further slamming the door on the dark matter-black hole theory.

"We are back to the standard discussions. What is dark matter? Indeed, we are running out of good options," said UC Berkeley professor of physics and astronomy, Uroš Seljak.

"This is a challenge for future generations."

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