Not long ago, scientists came up with the idea that dark matter may have formed stars, but we “can’t see”. This idea is not out of thin air, but has scientific evidence.
Is dark matter actually around?
First, we need to understand how scientists search for dark matter. One way to find dark matter is to build a xenon laboratory. In this lab, a special container holds liquid xenon, forming a trap. If a certain particle runs into the trap and hits the xenon atom inside, the atom will be knocked out of electrons and photons, and the mysterious particle will lose energy and be trapped in the trap. The knocked out electron It’s called a recoil electron. Scientists use the detection of recoil electrons to determine whether there are particles intruding, and then further search for intruding particles.
One day in June 2020, the xenon experiment in the Gran Sasso National Laboratory in Italy, which is looking for dark matter, was running as usual, but an accident happened. When scientists were doing recoil electron statistics, they found that a total of recoil electron events occurred. 285 times, 53 times more than predicted by dark matter theory. But after the experiment, the scientists did not find anything new in the trap.
Scientists have three explanations for the anomalous phenomenon of recoil electron events. The first is the intrusion of solar wind particles. The second is that the trap is contaminated with radioactive material in the experiment. The third and most novel explanation is that the anomaly in the recoil electron event is caused by some kind of boson.
According to quantum theory, there are only two types of particles in the universe: bosons and fermions. Electrons are typical of fermions, and photons are typical of bosons. In theory, there is a yet-to-be-discovered boson called an axion, which is passed directly by photons and has gravity, both of which are similar to those of dark matter. Therefore, scientists also speculate that the axion may be the dark matter itself.
If axions are indeed dark matter, then scientists can not only find new bosons, but also dark matter at the same time, which is literally killing two birds with one stone. It’s just that scientists haven’t dared to draw conclusions easily, because they just kicked the axion out of the dark matter candidate list not long ago. Also, while the third explanation is very appealing, the first and second explanations are also very convincing. So scientists involved in the xenon experiment are waiting for other colleagues to discover the same phenomenon after ruling out the first two possibilities.
In the meantime, however, astronomers have responded, arguing that a third explanation holds up because they discovered a strange black hole not long ago.
“Transparent” black hole
In 2019, the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States detected gravitational waves when two black holes merged. However, this gravitational wave is a little strange. According to previous theories, when black holes of ordinary matter collide and merge, they will go through the following three stages: the first stage, due to the distance is too far, the two black holes will slowly approach each other; the second and third stages are mergers, respectively and the formation of new black holes. However, in the detection of this black hole merger, astronomers could not detect the first stage anyway.
The absence of the first stage means that the two black holes collided directly. Astronomers were just beginning to think it was a new phenomenon of ordinary matter black holes. But astronomers calculated that if the first stage is removed, the gravitational wave signal from the black hole merger should not be as long as it is actually detected.
After learning about the previous boson speculation, astronomers replaced ordinary matter black holes with boson black holes and performed theoretical calculations. Then they found that if it was a boson black hole merger, it would be more consistent with the gravitational wave signal they detected.
What would a boson black hole look like? Based on existing theories, astronomers predict that, first, because bosons have gravity, boson black holes are as black as ordinary matter black holes, with a strong gravitational force that can grab light, and an accretion disk. Secondly, unlike ordinary matter black holes that swallow light, after boson black holes grab light, photons can freely penetrate stars, and boson black holes are smaller.
In addition, astronomers also predict that if boson black holes really exist, then there may already be boson stars in the universe. It’s just that because photons can easily penetrate boson stars, they are not detected by humans, like ghosts.
Today, astronomers are searching the universe for black holes that don’t look “normal”. They are also preparing to re-detect the supermassive black hole at the center of the Milky Way with the Event Horizon Telescope, which took the first picture of a black hole, to see if anything was missed. Astronomers even suspect that the supermassive black hole at the center of the Milky Way is actually a boson black hole, or a mixture of ordinary matter black holes and boson black holes.
Is there dark matter among the boson species? Do boson black holes exist? Are invisible ghost stars everywhere? These questions remain to be further explored.