One of the biggest questions in astronomy concerns the nature of dark matter. This component would be a type of matter that only interacts through gravitational interaction. It would not interact through the electromagnetic force, for example, so it would be impossible to observe it through light, which depends on these electromagnetic interactions.
Little is known about dark matter because it is only observed indirectly. Observations are limited to the effects of dark matter on the surrounding environment, such as the dynamics of stars or galaxies. One of the properties accepted by science was that the components of dark matter would not be collisional.
Airplane turbulence: global warming is increasing their frequency!
According to this property, known as cold dark matter (CDM), dark matter is non-collisional, that is, it does not exchange energy through collisions. An article has been published by a Spanish researcher who argues that there is an exchange of energy through collisions after simulations and observations of galaxy clusters. This argument argues in favor of a model called self-interacting dark matter (SIDM).
Black matter
Most of the matter in the Universe is in the form of dark matter. This is a type of matter that we cannot observe through electromagnetic radiation, that is, light. The matter we can observe is called visible matter or baryonic matter and is made up of everything we know and see in the Universe.
It is estimated that 85% of the matter in the universe is in the form of dark matter, while only 15% is in the form of visible matter.
Dark matter gained power after observing the dynamics of stars in galaxies that followed a different velocity curve than expected by theory. This discovery was made by astronomer Vera Rubin. To explain Rubin’s observations, dark matter was proposed as a halo of matter that encompasses the galaxy and interacts gravitationally with stars.
Cold dark matter?
Over time, more indirect observations of the effects of dark matter have been made in galaxies and galaxy clusters. Galaxy clusters can contain up to thousands of gravitationally interacting galaxies. By observing the dynamics of these galaxies and comparing them to the speeds proposed in the theory, the existence of a dark matter component was found to be necessary. Translated with DeepL.com (free version)
Based on observations of these interactions, a model of dark matter has been strengthened, called cold dark matter or CDM. According to this model, there is no energy exchange between dark matter components through collisions. One such sighting is the famous Bala Cluster, which recently underwent interaction. By analyzing observational data, astronomers say that there was no collision between the dark matter halos of each galaxy present.
SIDM
Although the CDM model is currently the most widely accepted because it explains many observations, some astronomers around the world argue for the self-interacting dark matter model, or SIDM. In this model, the components of dark matter would be collisional and there would be an exchange of energy between them other than simple gravitational interaction.
New study reveals details about the composition and structure of Earth’s inner core
During an interaction between galaxies, the SIDM model would present properties different from those expected by the CDM model. One of them would be that, when calculating the point of maximum dark matter density, it would show a separation which would be explained by the collision of the particles of each dark matter halo.
El Gordo
One of these interactions would occur in the cluster known as El Gordo, which is one of the most massive clusters ever discovered. The cluster has approximately 1 quadrillion solar masses. It is considered a true laboratory for observing interactions between galaxies and how dark matter affects the dynamics of galaxies during a possible collision.
Two subclusters within El Gordo draw attention to these observations. The astronomer found that the X-ray images show a peak and two elongated parts. Additionally, the X-ray peak is different from the estimated maximum dark matter peak, indicating a possible collisional component.
Simulations
To test the SIDM model, the article presents numerical simulations of N bodies. This type of simulation takes into account gravitational and collisional interactions between different components having mass. These are also hydrodynamic simulations that describe the dynamic behavior of gases present with properties such as density, pressure and temperature.
Melting permafrost in Siberia: are we ready for the future it reveals?
The paper states that the results show that dark matter appears to have a collisional characteristic in these observations. This would constitute evidence in favor of the SIDM model. If confirmed, it would be one of the biggest advances in understanding dark matter in recent decades.
Article reference:
Valdarnini 2024 An N-body/hydrodynamical simulation study of the merging cluster El Gordo: A compelling case for self-interacting dark matter? Astronomy & Astrophysics
