![]() "Those could still be 1% to 10% of dark matter … and there's still a window at lower masses, like the mass of a very small asteroid." "There are still some masses where the constraints are weak, around 20-30 solar masses," Bird told Live Science. Was this the final nail in the coffin? Is Hawking's theory really dead? Not so, according to Bird and Takada, who say that primordial black holes of a certain range of masses still haven't been totally eliminated as candidates. ![]() "This work rules out primordial black holes as dark matter in a range of masses where the previous constraints were not as strong nor as robust as this new one. "Microlensing is the gold standard for detecting black holes or ruling them out," said Simeon Bird, a black- hole physicist at the University of California - Riverside, who was not involved in the work. If primordial black holes made up a significant fraction of dark matter, Takada said, they should have seen approximately 1,000 microlensing signals. They found just one potential microlensing event. Takada and his team took about 200 pictures of the Andromeda galaxy over 7 hours on a clear night. The HSC is "unique," Takada said, in that it let them take images of all the stars in the Andromeda galaxy at once, at breathtakingly fast (to astronomers) exposure intervals - each interval was just 2 minutes long. ![]() That means their flashes would be much shorter. "If a microlensing object has, let's say one solar mass," Takada told Live Science, referring to the mass of the sun, "the timescale is like a few months or a year." But the primordial black holes they were looking for had only a small fraction of that mass, approximately the mass of the moon. A black hole passing in front of that star will distort its light, making it flash the smaller the black hole, the quicker the flash. Telescopes find microlensing black holes by taking many different pictures of a star over time. Instead, searching for small black holes means looking for places where their powerful gravitational fields bend light - a phenomenon called microlensing. Primordial black holes, however, are billions of times smaller and have no visible, glowing matter surrounding them. Masahiro Takada and his team at the Kavli Institute for the Physics and Mathematics of the Universe in Japan used this camera to search for primordial black holes their results were published earlier this month in the journal Nature Astronomy.īlack holes emit no light, though, supermassive black holes, like the one at the heart of galaxy Messier 87, are fringed by bright disks of hot matter. The Hyper Suprime-Cam (HSC) digital camera on the Subaru telescope in Hawaii is an advanced piece of imaging technology that can take a picture of the entire Andromeda galaxy (the nearest galaxy to our own) in one shot. But as technology has improved, scientists have been able to take sharper and sharper pictures of outer space. Until now, this theory could only be tested for primordial black holes heavier than the moon.
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