June 28, 2022
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Dark matter can become more and more mysterious; understand

* This text was written by a columnist from TecMundo; Learn more at the end.

Before explaining the title, we can review what is believed to be dark matter. First, that a massive body attracts another massive body has been known since Isaac Newton’s law of universal gravitation. On a cosmic scale, this attraction between objects directly affects the way planets, star systems, and galaxies move through the universe.

However, the motion of galaxies is much more complex than the law of gravity can describe. We must also take into account Albert Einstein’s general theory of relativity which, in a simplified way, provides a “better explanation” for the gravity exerted between planets, stars and galaxies, and is therefore more reliable for predicting such motions. However, there are more complex things in the universe that are not addressed in Einstein’s theory.

In systems like our own solar system, the closer a planet is to the sun, the faster it travels through space, that is, the time it takes Mercury, the closest planet to the sun, to go around the sun, much less than the time it takes Earth to complete the same revolution. This phenomenon has been known and expected since the seventeenth century by Kepler’s laws.

However, when dealing with galaxies, such as our Milky Way, which also has a center around which the stars rotate (where each star has its own planetary system), the same does not happen. That is, stars farthest from the center of galaxies travel through space at roughly the same speed as stars more central. It’s as if something is helping these stars move faster!

(stock struggle)source: stock struggle

Hence the hypothesis of dark matter, which consists of something that does not interact with electromagnetic radiation (light) but interacts gravitationally with stars and planets. One of the results of this interaction will be the speed exceeding the expected speed of stars far from the centers of galaxies, which was first observed in the 1930s.

However, the presence of this substance must be revealed to prove the gravity it exerts on the stars. Something, by the name chosen and to no one’s surprise, is not at all simple. In 1997 and onwards in 2013, using DAMA detectors, which were assembled specifically to search for dark matter. dark matter), scientists claimed that they were able to measure the particles of dark matter passing through the Earth as they travel through space at the moment when their speed is the greatest possible.

The results of the DAMA detectors, meanwhile, were encouraging, because they are not only a technical advance, but also because they confirm an old hypothesis, and also controversial, since other scientists have not been able to carry out the same dark matter measurements.

So far, although controversial, these have been the best results obtained for detecting dark matter. However, a November 2021 report in Science claims that a new, more accurate detector, called COSINE, is not detecting any of the signals that the scientists responsible for the DAMA projects have claimed.

COSINE dark matter detector.
COSINE dark matter detector (Yale/Handout)

The effect of dark matter not being detected might make this hypothesis even more ambiguous, either because we still lack sufficient technology or we may be looking for answers in the wrong places. However, in science, we cannot rule out any fact. In the event that the signals measured by the DAMA project are sure not even related to dark matter, it is always worth asking: What was captured?

Rodolfo Lima Barros Souza, professor of physics and columnist for the magazine TecMundo. He holds a Bachelor’s degree in Physics and a Master’s degree in Science and Mathematics Education from Unicamp in the field of public awareness of science. He is on social networks with the name @rodolfo.sou