One of the most famous theories of Stephen Hawking about dark matter has been shaken after the publication of the results of a Japanese team of astrophysicists led by Masahiro Takada of the Physics and Mathematics Institute of the Universe in Kavli, Live Science reports. The famous physicist who left this world last year believed that this mysterious and invisible substance consists of primordial black holes that appeared immediately after the Big Bang. Japanese scientists using the Subaru telescope conducted an experiment, the results of which, although they do not completely refute Hawking's theory, but admit that these black holes must be really tiny to explain the nature of dark matter.
Dark matter is the term physicists have given for a mysterious substance that, in their opinion, could explain one interesting fact: everything in the universe moves and rotates as if it contains more mass than we can detect. Different scientists at different times tried to attribute the properties of so-called dark matter to different objects. In the 1970s, Stephen Hawking and colleagues suggested that the Big Bang could create a large number of relatively small black holes - each the size of a proton. These tiny celestial bodies are difficult to see, but they will exert strong gravitational effects on other objects - two known properties of dark matter.
Until now, this theory could only be tested for primordial black holes, the mass of which is greater than the lunar one. But with the development of technology, scientists have been able to get more and more clear images of outer space. For their new study, a team of Japanese astronomers used the Hyper Suprime-Cam (HSC) camera mounted on the Subaru telescope in Hawaii. With its help, they took pictures of all Andromeda, the nearest galaxy to us, trying to find these small objects. The result of their work was published in the journal Nature Astronomy.
Black holes do not emit light, but supermassive black holes like the one at the center of galaxy M87, which scientists recently photographed, are surrounded by bright accretion disks of hot matter. But since primordial holes are billions of times smaller in size and have no visible luminous matter surrounding them, they can only be found by observing the powerful gravitational fields they create, which distort the radiation of neighboring objects. This phenomenon is called microlensing.
Telescopes are capable of detecting the microlenses of black holes by continuously surveying the stars. When the black gifts pass in front of the observation point and the star, it distorts the light of the star, causing it to "flash". The smaller the black hole, the faster this outbreak occurs.
However, the primordial holes that the Japanese team were looking for have only a fraction of this mass - it is approximately equal to the mass of our Moon. This means that the outbreaks observed should be much shorter.
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Takada calls the HSC camera unique, because with it, scientists were able to capture images of all the stars of the Andromeda galaxy at a time with a minimum exposure of about 2 minutes. In total, astronomers were able to get about 200 pictures of Andromeda in 7 hours on a clear night. They ended up only finding one putative microlensing event. If primordial black holes account for a significant proportion of dark matter, Takada said they should have seen about 1,000 microlensing signals.
Does this mean that Hawking's theory has been completely disproved? Takada and Bird are in no hurry to come to conclusions. According to them, the results obtained still cannot completely exclude the existence of primordial black holes, since, due to their small mass, the flashes of their signals would be too short to record them. According to researchers, it is necessary to develop new tools that would allow them to be discovered.
At the same time, scientists note that the detection of even one such signal could be crucial for future research, which will revolutionize some of Hawking's theories.
Nikolay Khizhnyak