by Using a fleet of next-generation satellites, scientists may soon be able to detect the most mysterious entity in the universe, according to a new theoretical study.
Dark matter — a poorly understood substance that does not emit, absorb or reflect light but exerts a clear gravitational influence on other matter — dominates the universe. Despite being more than five times more abundant in space than normal matter, the composition and properties of dark matter remain unknown.
To address this problem, Hyungjin Kim, a theoretical physicist at Germany’s Electron Synchrotron accelerator (DESY), proposed searching for dark matter particles using gravitational detectors – instruments designed to detect subtle leaks in the fabric of the universe. first predict space-time measurement. Albert Einstein.
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Dark matter as waves
There are many hypotheses about the nature of dark matter particles, which accumulate in huge quantities to form so-called halos in galaxies. In the new paper, published in December 2023 in the Journal of Cosmology and Astroparticle Physics, Kim assumed that these particles could be extremely light, as predicted by many popular dark matter theories.
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“Ultralight particles are commonly seen in many theories outside the Model,” Kim told LiveScience via email. Some of these particles are “perfect candidates” for dark matter, which raises some interesting implications for how the elusive entity might behave, he said.
“Unlike other ‘particle’ candidates for dark matter, ultralight dark matter particles behave more like classical [electromagnetic] waves,” Kim said.
The wave properties of dark matter can lead to unexpected behaviors. In particular, recent theoretical studies suggest that there should be random changes in the density of dark matter within a galactic core, affecting entire galaxies and possibly leaving subtle clues about the composition of dark matter.
“Imagine waves in the ocean; we see all the time that there are fluctuations on the surface of the ocean, and it changes in unpredictable ways,” said Kim. “The same thing would happen in the ultralight dark matter halo,” and the resulting fluctuations could extend millions of times the distance between Earth and the sun, Kim added.
If the dark matter is ultralight, and if it indeed behaves as a wave, scientists could detect its movements with gravitational wave detectors.
Gravitational wave detectors come to the rescue
According to Einstein’s theory of general relativity, gravitational waves are ripples in the fabric of space-time.
When such a wave passes through a gravitational wave detector, it changes the geometry of the space inside, temporarily changing the distance between two mirrors or other similar objects placed inside the detector. This minute change enables scientists to detect the presence of gravitational waves.
In his study, Kim suggests that this distance could be changed not only by a gravitational wave but also by the fluctuation of moving dark matter, which could attract the mirrors with its gravitational field like humans attract celestial bodies to Earth traveling around it.
“These fluctuations move randomly within the solar system, and they continuously bombard gravitational wave detectors,” Kim said.
To see if modern gravitational wave detectors could theoretically detect the influence of ultralight dark matter, Kim calculated how dark matter particles of different sizes could disrupt spacetime. Kim had to explore a wide range of masses — between 16 and 28 orders of magnitude smaller than the mass of an electron.
His theoretical analysis showed that for all these masses, existing detectors such as the Laser Inter-Gravitational Observatory (LIGO), which helped prove the existence of gravitational waves in 2015, would not be able to detect dark matter fluctuations because their sensitivity is too sensitive. low.
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However, there are several projects for future gravity detectors that will be located in space, and the distance between their satellites will not be several miles, like the distance between LIGO’s mirrors, but about a million times more. If this distance changes even by a small fraction, the magnitude of the change should be so large that the effect of dark matter should be measurable.
“What I discovered is that the bombardment of dark matter fluctuations could leave a distinctive signal in gravitational detectors, and future spaceborne detectors might be able to test the ultralight dark matter hypothesis,” Kim said. “My proposal uses future space-borne gravity detectors, such as Laser Interferometer Space Antennas (LISA).”
With LISA currently scheduled for launch in the mid-2030s, this theory could be more than a decade away from being testable. Kim said, however, that in the meantime there may be other ways to detect the influence of dark matter on space-time.
“I am currently investigating the prospect of rapidly rotating neutron stars as another way to investigate such fluctuations,” he said.
