Discovery of 'dark dwarf' could open door to decoding the mystery of dark matter

DNVN - A newly published study shows that mysterious “dark dwarfs” may provide important clues, contributing to clarifying the true nature of dark matter – one of the biggest mysteries of modern cosmology.

A proposed new class of stellar objects, called dark dwarfs, may be lurking at the center of our galaxy. These faint, low-mass stars may be powered not by nuclear fusion, but by the annihilation of dark matter particles, which could reveal the elusive nature of one of the universe’s greatest mysteries. (Artist’s concept). Source: SciTechDaily.

Published in the Journal of Astrophysics and Nuclear Astrophysics, the team of researchers from the UK and Hawaii introduced the concept of dark dwarfs and described how humans can detect them using existing instruments, including the James Webb Space Telescope. The name “dark dwarfs” is not because they are inherently dark, but because they are intimately tied to dark matter – a matter that remains at the heart of astrophysics and cosmology today.

“We think that 25% of the universe is made up of a type of matter that does not emit light, making it invisible to the naked eye and to telescopes. We can only detect it through its gravitational effects. That’s why we call it dark matter,” explained study co-author Professor Jeremy Sakstein of the University of Hawaii.

Although the existence of dark matter has been confirmed and scientists have observed its behavior, its true nature remains a mystery. Over the past 50 years, many hypotheses have been proposed, but none have been supported by strong experimental data. Studies like this one aim to provide practical methods to get closer to a final answer.

Among the leading candidates for dark matter are Weakly Interacting Massive Particles (WIMPs) – particles with extremely large masses that interact very weakly with ordinary matter. They pass through everything almost undetected, do not emit light, are not affected by electromagnetic forces, and therefore do not reflect light and remain invisible. WIMPs can only be detected indirectly through their gravitational influence. This is also the type of dark matter necessary for the existence of dark dwarfs.

Illustration of a black dwarf. Source: Image created by Sissa Medialab staff using Adobe Illustrator

“Dark matter can interact gravitationally, so it gets trapped by stars and accumulates inside them. When that happens, it can interact with itself and annihilate itself, releasing energy that heats the star,” Sakstein explains.

Regular stars, like the Sun, shine through nuclear fusion in their cores, when they are massive enough for gravity to compress matter to the point where it triggers reactions between atomic nuclei, releasing enormous amounts of energy that we see as light. Dark dwarfs, on the other hand, also shine, but not through nuclear fusion.

“Dark dwarfs are very small, only about 8 percent the mass of the Sun,” Sakstein said. Such low masses are not enough to start fusion reactions. So these objects, though common in the universe, usually emit only a faint glow from the energy generated by their small gravitational collapse, and are called brown dwarfs.

However, when they exist in regions rich in dark matter, such as the center of the Milky Way, brown dwarfs can transform into other forms. “These objects collect dark matter, making them dark dwarfs,” Sakstein emphasized. “The more dark matter around them, the more they collect. And the more dark matter they accumulate, the more energy they can generate from their annihilation.”

But all of these theories only work for a certain type of dark matter. “For dark dwarfs to exist, dark matter must be made of WIMPs, or any massive particles that can interact with themselves to create visible matter,” Sakstein said. Other theories, such as axions, sterile neutrinos, or faint ultralight particles, are too light to produce the desired effect. Only massive particles that can interact and annihilate into visible energy would provide enough energy for dark dwarfs.

But for this hypothesis to be valid, a specific method for identifying dark dwarfs is needed. So Sakstein and his colleagues propose a signature: Lithium-7. This is an element that burns very rapidly in normal stars and quickly disappears. “If you find an object that looks like a dark dwarf, you can check for traces of Lithium-7. If it’s still there, it can’t be a brown dwarf or something like that,” Sakstein explains.

Modern instruments like the James Webb Space Telescope are thought to be able to detect extremely cold objects like dark dwarfs. Sakstein suggests a different approach: “Another option is to look at the entire population and then ask statistically whether an additional population of dark dwarfs should be included to better characterize it.”

If scientists identify one or more dark dwarfs in the coming years, will that be enough to support the hypothesis that dark matter is made up of WIMPs? “Quite strongly,” Sakstein replied. “With light dark matter candidates, like axions, I don’t think we’ll find anything that looks like a dark dwarf. They don’t accumulate inside stars. If we find dark dwarfs, it would be strong evidence that dark matter is massive and interacts strongly with itself but only weakly with the standard model. This includes WIMPs and some other exotic models.”

However, he also noted that the discovery of dark dwarfs does not necessarily mean that dark matter is a WIMP, but it could be a WIMP or another form of matter that behaves closely like a WIMP.

If this hypothesis is confirmed, it would open up new research directions, potentially shedding light on one of the universe's greatest mysteries.

La Khe (According to SciTech Daily)

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