None of the universe’s dark matter consists of heavy black holes or any similar object, including massive compact halo objects (MACHOs), says scientists, challenging previously held notions.
After the 2015 detection of gravitational waves from colliding black holes, astronomers held out hope that the universe’s mysterious dark matter might consist of a plenitude of black holes sprinkled throughout the universe.
However, physicists from the University of California, Berkeley, based on statistical analysis showed that primordial black holes can make up no more than 40 percent of the dark matter in the universe.
They analyzed 740 of the brightest supernovas discovered as of 2014, and found that none of them appear to be magnified or brightened by hidden black hole “gravitational lenses”.
The results, published in the journal Physical Review Letters, suggested that primordial black holes could only have been created within the first milliseconds of 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 km across.
“We are back to the standard discussions. What is dark matter? Indeed, we are running out of good options,” said Uros Seljak, Professor at the varsity. “This is a challenge for future generations.”
Dark matter is one of astronomy’s most embarrassing conundrums: Despite comprising 84.5 percent of the matter in the universe, no one can find it.
Proposed dark matter candidates span nearly 90 orders of magnitude in mass, from ultralight particles like axions to 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.