It is possible that dark matter holds a secret even darker than that. Researchers are comparing the behavior of the hypothesized dark matter with actual galaxies.
Dark Matter and Cold Dark Matter
The deepest secrets of dark matter relate to its nature and behavior. The prevailing idea about dark matter is the Cold Dark Matter (CDM) theory, which assumes that dark matter is composed of low-velocity particles that do not interact with each other. This belief has been discussed and is under debate once again. A team of researchers from the University of California, Riverside, led by astronomer Hai-Bo Yu, proposed an alternative idea to explain two extreme cases where cold dark matter does not work well.
Self-Interacting Dark Forces
Galaxies and clusters of galaxies are thought to be surrounded by crowns of dark matter. On one side of the debate, there are dark matter crowns in galaxies that are too dense to be consistent with CDM, and on the other side, there are dark matter crowns in galaxies that are too diffuse for CDM to explain. Instead, Yu and his colleagues suggest that some dark forces make dark matter particles collide with each other. This is self-interacting dark matter (SIDM).
Cold Dark Matter and Hot Dark Matter
Why is it overwhelmingly believed that dark matter is cold? Dark matter is “dark” because its interactions with visible matter and electromagnetic radiation are weak or nonexistent. Light cannot illuminate it because it is unable to interact significantly with any type of electromagnetic radiation. The reason dark matter is considered “cold,” at least according to the cold dark matter theory, is that slow-moving particles travel slower than the speed of light.
CDM still remains the standard model of dark matter because it works to build and maintain cosmic structures such as galaxies. If dark matter is cold, it can clump and coalesce more easily than if it were moving in the cosmic void – which it would be if all dark matter were “hot” or composed of lighter particles traveling at high speeds. Hot dark matter particles would be too swift to form structures over long periods and would flatten any existing structures they encountered. Warm dark matter lies somewhere between cold and hot.
Self-Interacting Dark Matter and Explanation
The number of types of dark matter that exist is unknown. Some scientists insist that all dark matter is cold, while others argue that there is more than one type.
While CDM does not claim that this completely invisible matter is static, it does not allow for the collision of many dark matter particles. This is where self-interacting dark matter comes in.
In their study, Yu and his team tested whether self-interacting dark matter could explain an aspect of cold dark matter that does not really work: it struggles to explain the extremely dense and extremely diffuse dark matter crowns.
The dark matter crowns in very small galaxies extend much farther than those of regular small galaxies, which should not happen with the non-colliding particles proposed by CDM – non-interacting particles would be closer together and produce denser and shorter-range crowns. Self-interacting dark matter allows particles to collide and transfer heat, and it may explain the resulting expansion of dark matter why these crowns are so diffuse.
The second scenario deals with extremely dense dark matter crowns affecting gravitational lensing. These dense crowns contain enough dark matter to warp spacetime, causing light to bend through that region of space as well. Because of these distortions, the object behind a specific galaxy is magnified, albeit often in a somewhat distorted manner. Self-interacting dark matter also supports sufficient concentrations of dark matter to affect gravitational lensing because colliding particles must move inward just as they move outward. Collisions between particles increase the density of the crowns, and a collection of them can form a massive dark matter mass that produces a gravitational lens.
What
We are still in the dark about dark matter in many ways. Until we can detect it directly, we have to rely on theoretical work to see if ideas like self-interacting dark matter have uncovered anything. Perhaps one day, we will have a direct detection method that will finally reveal the secrets of dark matter.
Source: Astrophysical Journal Letters, 2023. DOI: 10.3847/2041-8213/ad0e09
Source: Elizabeth Rayne is a writer. Her work has appeared in SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. She lurks outside of New York with her parrot, Lestat. When she’s not writing, she is either shapeshifting, drawing, or dressing up as an obscure character. Follow her on Threads and Instagram @quothravenrayne.
Source: https://arstechnica.com/science/2023/12/dark-matter-might-be-keeping-an-even-darker-secret/
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