What is the Rarest Substance in the Universe?

Dark matter (including dark energy) is considered to be the most challenging riddle in the study of the universe. It represents more than 90% of the material content in the universe, and the visible world only accounts for less than 10% of the material in the universe. Dark matter cannot be observed directly, but it can interfere with light waves or gravitational forces emitted by stars, and its existence can be clearly felt.

Cosmic dark matter

Decades ago, the universe

Scientists have put forward various hypotheses about the characteristics of dark matter, but they have not been tested sufficiently. The Space Telescope Institute of Johns Hopkins University in the United States has observed the light emitted by galaxies further away in two clusters of galaxies with the help of an "advanced mapping camera" installed on the "Hubble" space telescope three years ago. The phenomenon of gravitational lensing caused by the interference of dark matter in the medium, and then through computer simulation, the distribution map of dark matter is obtained. These two emerging galaxy clusters are located in the southern sky dome, about 7 billion light years from Earth, and each have about 400 galaxies. The so-called gravitational lensing phenomenon means that when light passes near a gravitational celestial body, it bends like passing through a convex lens. In theory, dark matter can also cause the phenomenon of gravitational lensing, but its effect is very weak. Only high-sensitivity observation equipment such as "advanced mapping cameras" can take pictures, and ground-based astronomical telescopes can be difficult to see because of atmospheric interference. The researchers published the results in the Journal of Astrophysics to be published on the 10th. The first author of the paper, Dr. Hanji Chi, an assistant researcher of Korean descent, said that the images they obtained clearly show that the visible matter (that is, the two galaxy clusters observed) is surrounded by a network of dark matter, which is the most dense of dark matter. The place is like the foam at the top of the waves. They believe that this supports the conjecture that dark matter and visible matter will gather together under the effect of gravity, that is, where dark matter concentrates will attract visible matter, thereby helping the formation of stars, galaxies, and galaxy clusters. The distribution map also shows that dark matter is densely packed in clusters. Based on this, the researchers believe that this verifies the assumption that dark matter particles are "non-collision particles", that is, if dark matter particles come together, they will not bounce like classic particles such as molecules and atoms, but will continue to do "nothing". motion. They explained that if dark matter particles collide with each other, they will be more evenly distributed after frequent collisions, rather than densely clustered. Scientists have long agreed that the vast universe is composed of dark matter, dark energy, and normal matter that we humans can perceive. Among them, normal matter is the least, accounting for only 4%, dark matter is second, accounting for 23%, and the rest are dark energy . As the name suggests, dark matter is something that humans cannot see. Although scientists have long determined the existence of dark matter and galaxies composed of dark matter, they have not found them, let alone which particles they are composed of. Therefore, this discovery actually revealed a big secret of the universe and was a major discovery. A galaxy made of dark matter is as massive as a normal galaxy, such as our Milky Way, and rotates in cosmic space. However, it is different from normal galaxies. There are no glowing stars in it, and people cannot see it. So, how did scientists discover the galaxy they named "Virgo HI21"? It turned out that the data observed by a radio telescope can be used to estimate the rotation speed of a galaxy. They found that the "Virgo HI21" galaxy has a large rotation speed, and inferred that its mass is greater than that composed entirely of normal matter. Furthermore, scientists have estimated that the mass of this "Virgo HI21" galaxy is 100 million times that of the sun. Although this mass is not very large for a galaxy, if it is composed of normal matter, it should contain bright stars. It is bright, but it is dark, indicating that it does not contain stars. So scientists have come to the conclusion that the galaxy is composed of dark matter.