Dark matter - the mysterious element that constitutes the universe

We only know a very small part of the material that constitutes the universe. A huge part called "dark matter" has not been fully discovered.

The mystery of no solution of dark matter

When they discovered the structure of atoms, scientists thought they understood the whole thing that constitutes the universe . However, in 1933, Swiss astronomer Fritz Zwicky suggested that much of the material that constitutes the universe is not ordinary matter, but something completely different.

Atomic structure of "normal" matter.(Photo: Michael Gilbert / SPL)

Zwicky made this speculation after observing a few groups of galaxies with very fast rotational speeds, if only normal matter would be scattered throughout the universe by the action of centrifugal force. The gravitational pull of all ordinary matter in these galaxies is not enough to keep them stable.

Scientists later used the term " dark matter " to refer to this group of matter. However, at the time, Zwicky's idea was considered eccentric and not thoroughly studied.

" People consider him a mad scientist, trying to think of a new kind of material when unable to explain the phenomenon by ordinary forces, " said Dr. Richard Massey, of Durham University.

Zwicky's thesis was forgotten until the 1970s, when astronomer Vera Rubin discovered that our nearby galaxies did not turn in the normal way.

In the solar system, there is a simple rule. The farther away from the Sun, the slower the rotation speed of the planets is due to the gravitational pull. This rule should also be true for stars spinning around the center of the galaxy. The farthest stars will have to move at the slowest.

However, according to Rubin observes, distant stars also orbit the center of the galaxy as fast as nearby stars. And because of the high speed of rotation, there must be something to hold it in orbit, without being thrown out. Astronomers now agree that "something" is dark matter, the basic constituent of the universe.

Fritz Zwicky, the first to propose the theory of dark matter.(Photo: Emilio Segre Visual Archives)

Nearly 14 billion years ago, after the Big Bang , the universe began to expand rapidly and galaxy clusters formed. At that time, dark matter was like an invisible anchor, keeping the universe from expanding too quickly and galaxies not scattered. It is possible to imagine dark matter like the wind, people cannot see it but know it exists. Estimates of dark matter account for about 25% of the universe. And only about 30% of the universe is matter, the rest is energy.

The first evidence of the existence of dark matter began to appear in the 1980s. In 1981, the Harvard University team discovered that galaxies were not arranged in a uniform pattern. . Instead, they congregate in large clusters, each with hundreds to thousands of galaxies, forming "space networks" . These networks are tied together by dark matter. In other words, dark matter is a " skeleton" to hang ordinary matter, according to Dr. Carolin Crawford, University of Cambridge.

"In the early universe, dark matter played a very important role in keeping galactic clusters from being dispersed, so that the universe evolved as we see it today," she said.

Fornax galaxy cluster, kept stable by dark matter.(Photo: NASA / JPL)

On the nature of dark matter, people initially thought it was neutrinos. These are mysterious "dark" particles, hardly interacting with any other particle. The researchers propose the idea that the total mass of all neutrinos in the universe is the missing gravitational mass to balance. However, if so, neutrinos will be " hot dark matter", meaning they are very light and have a high movement speed.

Dr. Carlos Frenk, Durham University, when trying to simulate the universe with hot dark matter found that this hypothesis could not happen. "The universe with hot dark matter is completely different from the real universe ," he said. From here, scientists came to the conclusion that dark matter must be "cold" and move slowly.