Observations of the oldest stars in the Galaxy have helped astrophysicists find out that the speed of movement of dark matter in the vicinity of the Earth and the Sun is unexpectedly low, making it difficult to find it in the future, according to an article published in the journal Physical Review Letters.
“When a particle of dark energy collides with the nucleus of an atom of 'ordinary' matter, the process of their collision resembles what happens when two billiard balls hit each other. The consequences of this "accident" depend on two parameters - the mass of the particles and the speed of their movement. In other words, the faster dark matter moves, the more noticeable its traces will be,”says Mariangela Lisanti from Princeton University (USA).
For a long time, scientists believed that the universe consists of visible matter, which forms the basis of stars, black holes, nebulae, dust clusters and planets. But the first observations of the speed of stars in the galaxies closest to us showed that the stars on their outskirts move at an impossibly high speed - about 10 times higher than calculations based on the masses of all stars showed.
The reason for this, according to scientists, was the so-called dark matter - a mysterious substance, which accounts for about 75% of the mass of all matter in the universe. Typically, each galaxy contains about 8-10 times more dark matter than is visible, and this dark matter holds the stars in place and prevents them from "scattering".
In recent years, thanks to Hubble's images of some relatively poorly studied galaxies, scientists have begun to notice that many small and dwarf galaxies behave quite differently from what theories predict, taking into account the existence of this mysterious substance.
Additional problems, as Lisanti notes, are created by the fact that today astronomers and cosmologists do not know how fast dark matter moves in our Galaxy and in its closest neighbors, which significantly complicates the work of "direct" dark matter detectors trying to catch traces of its collisions with atoms of xenon-137 and other rare noble gases.
Her team found a way to solve this problem by drawing attention to an interesting fact from the life history of the most ancient stars in the Milky Way. These luminaries, as astronomers note, were born about 10-12 billion years ago, at a time when our Galaxy was just beginning to form and was actively absorbing the neighboring dwarf galaxies.
At that time, according to the researchers, the so-called halo - a "donut" of dark matter that surrounds the Milky Way and other stellar metropolises - had not yet formed, as new supplies of this mysterious substance constantly flowed into the Galaxy, accompanied by clouds of gas and newborn stars.
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For this reason, the elderly luminaries living today on its outskirts must, on average, move at the same speed with which dark matter revolves around the center of the Milky Way, which can be used to calculate this parameter, without having a clue about other properties of this mysterious substance.
Guided by this idea, scientists tried to calculate the speed of movement of dark matter in the vicinity of the Earth using a map of the night sky prepared by the SDSS project and a computer model of the Galaxy.
These measurements unexpectedly showed that clouds of dark matter located near the solar system should move noticeably slower than theory predicts. Such discrepancies, as Lisanti and her colleagues point out, indicate serious gaps in theory that could greatly impede physicists in their search for traces of this elusive substance.