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Humanity can be called an ambitious species. We live on a small planet revolving around an ordinary star and yet we strive to unravel all the mysteries of the universe. Take, for example, dark matter. It is believed that it makes up most of the matter in galaxies, but it is impossible to observe it – this mysterious substance does not interact with electromagnetic radiation. We know about its supposed existence due to the gravitational effect it has on the objects we observe. Today, both dark matter and dark energy are the main pillars of the leading cosmological model. Recently, a study was published in the journal Astronomy and Astrophysics listing evidence for the existence of dark matter in the very first galaxies in the universe. But if the scientists are wrong and no dark matter/energy actually exists, our ideas about the structure of the universe will have to be revised. And this, you see, is serious.
The search for invisible matter
In the 1970s, astronomers Vera Rubin and Kent Ford presented a new theory that could explain the observed behavior of stars, planets, and galaxies. They suggested that some invisible substance has a strong gravitational effect on visible celestial bodies. According to Rubin and Ford, this “dark matter” holds space objects together, as if gluing them together.
The researchers also tried to understand why celestial bodies located outside the center of the galaxy rotate at the same speed as objects near it. This state of affairs contradicts Newton’s law, according to which stars and gas should slow down as they move away from the galactic center, but observations show that this is not the case, and the presence of mysterious matter can explain what is happening.
Ford and Rubin’s theory, however, has not gained general acceptance, and many researchers are still convinced that dark matter does not exist. NASA scientists are ready to argue with them – as the results of a new study show, there are a number of factors confirming the conclusions of the 1970s.
Dark matter inside galaxies
The presence of an invisible substance that “sticks together” stars and planets is changing our understanding of the universe. The fact is that observable matter in galaxies is only 20% – researchers call this matter baryonic (which means that it consists of such subatomic particles as protons, neutrons and electrons). The remaining 80% remain invisible and incomprehensible.
The authors of the work, published in the scientific journal Astronomy and Astrophysics, provide new evidence in favor of the existence of dark matter. At least 260 young spiral galaxies in which new stars are being formed became the object of the study.
Recall that the distance between our planet and the selected objects is approximately seven billion light years. This means that they formed when the universe was twice as young as it is today (the age of the universe is approximately 13.8 billion years). These galaxies are shaped like the Milky Way, with its spiral arms of stars and gas clouds.
Astronomers have been able to confirm that these young galaxies are surrounded by a halo of dark matter emanating from the galactic center. These halos, however, are much more compact than those of the galaxies closest to us, which means that the distribution of dark matter within galaxies is slowly expanding over time.
We believe that this phenomenon illustrates a direct interaction between dark matter particles and ordinary baryonic particles: the density of haloes changes and goes beyond known gravitational interactions, the researchers write .
Astronomers also point out that dark matter is responsible not only for the large-scale structure of the universe, but also for clusters of galaxies held together. Did you know that dark matter can hide in an extra dimension?
Dark matter alternative
Another group of researchers suggested that the situation around dark matter has changed – the answer should be sought in gravity itself. If you look closely at the universe full of galaxies, stars, dust, gas and black holes, you can find something already known. After all, if additional gravitational effects exist, something invisible could be responsible for them, for example, a fundamentally new type of matter or particles.
So, if the neutrinos were massive enough, they could well explain what is happening. Another option could be the birth of a universe with too much matter, some of which collapsed to form black holes. Options like these could put an end to the endless inconsistencies between the actual behavior of celestial objects and our physical theories.
Alas, these assumptions are hardly correct, since the total amount of baryonic matter in the Universe is already known. Some researchers are also proposing to rethink the theory of gravity in order to completely get rid of the dark matter. But if we want to unravel the mysteries of the universe, dark matter (and energy) should not be abandoned, at least not yet.
Note that scientists often discover something new that can challenge the prevailing theories. For example, the results of previous studies have shown that young star-forming galaxies seem to experience a deficit of dark matter (compared to later galaxies). For this reason, some physicists believe that dark matter plays a much smaller role in early star systems than in modern galaxies. However, to date, these assumptions are not consistent.
New dark matter detector
To find out whether dark matter exists, scientists will have to observe galaxies for a long time. Fortunately, new astronomical instruments, including the James Webb Space Telescope, are able to “see” our universe’s distant past, including the first stars and galaxies that formed shortly after the Big Bang.
Researchers have high hopes for the world’s most sensitive dark matter detector, LUX-ZEPLIN, which is located 1.5 kilometers underground and housed in a large tank of water to protect the LZ from collisions with other particles. As the name suggests, the detector is the successor to two previous projects, LUX and ZEPLIN, but its latest version is 50 times more sensitive to potential dark matter signals.
Among the candidates for the role of dark matter, researchers single out weakly interacting massive particles (WIMPs) born in the early Universe. If they really exist, then they interact with ordinary matter, creating already familiar astronomical anomalies. The new detector is surrounded by sensors that monitor any intrusion of the desired particles, and a reservoir of ultra-pure liquid xenon is used as a target.