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Astronomy

There are about 40 million, 000 black holes in the universe.

The number of black holes in the universe is one of the urgent questions to be answered in the field of modern astrophysics and cosmology. In a recent study published in the Astrophysical Journal, scientists calculated for the first time that the number of constant-star black holes (with masses ranging from a few to hundreds of solar masses that originated at the end of the life of massive stars). Most black holes in the universe belong to constant-star black holes, and it is estimated that there are about 400 billion black holes in the observable universe.

In this study, scientists integrate the empirical formulas of star and binary star evolution algorithms with the physical properties related to galaxies (especially the formation rate of stars, the number of constant star black holes and the metal content of interstellar media). The mass distribution of constant black holes in the history of the universe is obtained, based on which the number of black holes in the observable universe is obtained. The study also points out that about 1% of ordinary matter in the universe is "locked" in a constant star black hole. In addition, the team also explored the formation channels of black holes with different masses, including isolated stars, binary star systems and star clusters. This study lays a solid foundation for the further study of constant star black holes and their origin. (science and Technology Daily)

Ecology.

Illuminated fishing nets can reduce the chances of protected species such as sharks being caught.

Gillnet is one of the main fishing tools in global coastal small-scale fisheries, but because Gill nets do not distinguish anything that tries to swim past it, they often bycatch creatures that are not targeted by fishermen, including endangered and protected animals such as sharks, sea turtles, marine mammals, seabirds and other fish. These animals are often injured or died and then thrown back into the sea. Incidental capture of coastal Gill net fisheries has led to a decline in the number of endangered species worldwide, affecting coastal ecosystems. Past studies have shown that lighting Gill nets with LED lights can reduce incidental catch of endangered sea turtles because LED lights provide sensory clues to draw attention to fishing nets.

Recently, a study published in current Biology assessed the impact of illuminated fishing nets on incidental fishing and fishing efficiency. The researchers set a Gill net lit by a green LED light every 10 meters along the Pacific coast of Mexico and found that the incidental catch of illuminated Gill nets decreased by 63%, including 95% for sharks and rays, 81% for American squid, and 48% for unwanted finned fish, while the catch and market value of target fish were not affected. At the same time, the time it takes for fishermen to recover and unravel their nets has been reduced by 57 per cent, making the technology attractive to fishermen. This simple, relatively low-cost technology can protect endangered species and allow fishermen to fish in a more sustainable way.

Neuroscience

The neural mechanism of stress affecting sleep

Previous clinical studies have found that sleep disorders have a high prevalence of mental disorders related to stress and fear, and there may be significant changes in REM sleep state in these mental disorders. In a recent study published in the journal Neuron, scientists revealed the relationship between REM sleep and instinctive fear and stress.

The researchers conducted experiments in mice and found that REM sleep can specifically respond to natural enemy stimuli. They also successfully analyzed for the first time a "shared" neural loop that regulates REM sleep and instinctive fear response, which regulates the response to natural enemy stimuli during REM sleep. corticotropin-releasing hormone neurons not only play an important role in maintaining the stability of REM sleep, but also are particularly sensitive to dangerous information about natural enemies. In addition, the REM sleep structure of mice changed significantly under long-term stress. Nowadays, humans do not need to deal with natural predators, and the originally conservative natural enemy defense loop may be used to deal with external stimuli such as social stress, the researchers said. This "shared" neural loop provides a possible target for the treatment of sleep disorders and comorbidities of some mental disorders. (science and Technology Daily)

Psychology.

Image size can affect visual memory

Every day, we see all kinds of images on the wall, books or electronic devices, some of which impress us, others seem to be fleeting. At present, scientists do not know the factors that affect visual memory. Previous studies have suggested that visual memory has nothing to do with image size. But recently, a study published in the Proceedings of the National Academy of Sciences pointed out for the first time that visual memory of images can be affected by image size.

Geoscience

The gravitational pull of the sun on the moon will affect the plate motion of the earth.

The researchers believe that the sun has a strong gravitational pull on the moon, which lengthens the moon's orbit around the earth, bringing the center of mass of the earth-moon system closer to the earth's surface. So as the earth rotates, this creates pressure inside the earth, transforming the earth from a perfect sphere into a slightly flattened ellipsoid, eventually leading to the destruction of the lithosphere. The study also compared different Earth-like planets and found that the existence and duration of volcanic and tectonic activity on the planets depends on the size of the planet, the direction of the planet's orbit, and the distance from the sun.

Physics

Detection of X particles in quark-gluon plasma for the first time

Credit: Pixabay/CC0 Public Domain

At the moment of the Big Bang, the universe was made up of flowing quarks and gluons with temperatures as high as trillions of degrees Celsius and cooled to form more stable atoms and protons. In the chaos before cooling, some quarks and gluons collide randomly to form short-lived "X" particles. The structure of X particles is unknown and extremely rare, but a study published in physical Review KuaiBao recently detected X particles for the first time in quark-gluon plasmas in particle accelerators.

The researchers analyzed the 2018 data set of CERN's large Hadron Collider (LHC), which contains more than 13 billion collisions of lead ions, each of which releases quarks and gluons. These particles will be merged into more than 1000 trillion short-lived particles, resulting in a lot of background interference. In order to get rid of these background disturbances, the researchers developed an algorithm based on machine learning and trained the algorithm to identify the key variables of the unique decay pattern of X particles, thus in the dense and noisy high-energy particle soup data, more than 100 specific mass peaks of X particles were successfully screened. After estimating their mass, they named the X particles X (3872). In the future, they will collect more data to explore the structure of X (3872).