Dark matter remains one of the biggest puzzles in current science. The first clues pointing to its existence appeared as early as the 1930s, but were not enthusiastically received by the scientific community. It wasn’t until observations made 50 years later that the term “dark matter” became a permanent fixture in physics textbooks.

“This galaxy weighs too little”. 85 percent of the entire mass of the Universe is dark matter [1]

American astronomer Vera Rubin began observing the Andromeda Galaxy in 1970. She quickly concluded that, with its rotation, most of the stars far from the center should be free to fly off into space. However, the stars remained in place, indicating that the gravitational forces must be much greater than estimated. Where was the mass hiding that was generating them?

In her calculations, Rubin showed the mass that was invisible to scientists must be 5–10 times more than what could be observed. [2] In the following years, many astronomers confirmed the observational results by various methods. However, no one was capable of registering dark matter directly, even though observations of the distribution of objects in galaxies made it possible to determine the points in space where clusters of dark matter should be located. This gave rise to a hypothesis defining the fundamental characteristic of dark matter – the unknown particles that make it up interact with observable matter only at the gravitational level.

Although several detectors of dark matter particles have been built on Earth, it has so far been unobserved. The main candidates are the group of WIMPs or Weakly Interacting Massive Particles (WIMPs). However, many researchers are focusing on indirect methods of dark matter detection and investigating new ways to detect its presence. One proposal that has been around for 20 years is the interaction of WIMPs with neutrinos – other extremely difficult particles to observe, but which scientists have become much more familiar with.

Neutrinos – the key to understanding dark matter?

An international team of researchers decided to challenge the assumptions of this very method anew. One of them was Dr Sebastian Trojanowski from the international research agency AstroCeNT, CAMK PAN and the Department of Theoretical Physics at NCBJ. [3]

The results, in the form of an article, are available in full online [4] but an in-depth knowledge of particle physics is required to understand them. Fortunately, in a communication that appeared on the National Centre for Nuclear Research website, the author himself intelligibly explains what the team’s work consisted of.

The theoretical models of the sought-after dark matter particles most closely resemble neutrinos. In the early years of research in this matter, there was even a view that neutrinos produced at initial stages in the evolution of the Universe were responsible for the observed deviations. Current theories reject this possibility, but both neutrinos and the remnants of the Big Bang may prove crucial to understanding the mystery of dark matter.

Building a laboratory to study the interactions between the particles described is far beyond the limits of current technology. An excellent substitute turns out to be the microwave background radiation – a trace of energy from when the first atoms were formed. It is currently observed as an electromagnetic wave spectrum with an average temperature of just 2.7 K. The minor thermal irregularities give an insight into the distribution of matter in the early Universe. This, in turn, was, according to scientists, strongly related to the distribution of dark matter. An additional factor may have been the interactions between dark matter particles and neutrinos, which were then present in much higher densities.

Deviations in these distributions, which were first postulated theoretically as long as 20 years ago, had to wait for further developments in technology and more accurate methods of observing the microwave background radiation. The results of the research in which Dr Trojanowski was involved confirm these assumptions, as well as the results of another group on a series of absorption lines in the spectra of quasars and distant galaxies (the so-called Lyman-alpha forest). There, similar deviation values were also observed, and the researchers came to similar conclusions that can explain them. It is sufficient to assume a non-zero value for the interactions between neutrinos and dark matter.

“[…] Even if it has nothing to do with dark matter, it is possible that we are on the trail of some real phenomenon that awaits an explanation,” – comments Dr Trojanowski.

Dark energy research and the development of science

Although the article based on the research does not provide clear and spectacular answers, it is a crucial element on the road to unraveling  one of the greatest puzzles in the history of all science.

Understanding physical processes at such an elementary level is not only a chance to explore age-old questions about the origins of the Universe but in all likelihood a tremendous advance for physics as a whole. This directly translates into technological possibilities for human civilization.

The participation of Polish scientists in the search for key answers is of absolute value to national science, but the potential benefits go far beyond the walls of universities. Creating theoretical foundations for new discoveries may prove to be the ticket to participating in the development of breakthrough technologies resulting from them. 

For a Polish economy aspiring to become a European and world leader, the development of advanced technologies, know-how and production of their essential elements are among the key challenges and necessary conditions to be met.

Bibliography:

[1] NASA website, Dark Energy, Dark Matter, https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy, (accessed 28.10.2023)

[2] Carnegie Science website, Vera Rubin Who Confirmed “Dark Matter” Dies , https://carnegiescience.edu/news/vera-rubin-who-confirmed-%E2%80%9Cdark-matter%E2%80%9D-dies, (accessed 29.10.2023)

[3] NCBJ website, Neutrinos may be key to understanding dark matter, https://www.ncbj.gov.pl/aktualnosci/neutrina-moga-byc-kluczem-do-zrozumienia-ciemnej-materii, (accessed 28.10.2023)

[4] Brax, P., Van de Bruck, C., Di Valentino, E., Giaré, W., Trojanowski, S., New insights on ν-DM interactions, Monthly Notices of the Royal Astronomical Society: Letters, Volume 527, Issue 1, January 2024, Pages L122-L126, https://doi.org/10.1093/mnrasl/slad157, (accessed 28.10.2023)