A new theoretical study suggests that scientists may soon be able to detect the most mysterious being in the universe using a fleet of next-generation satellites.
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. Although it is five times more abundant in space than ordinary matter, the composition and properties of dark matter are still not fully known.
To solve this problem, Hyungjin Kim, a theoretical physicist at the German Electron Synchrotron (DESY) accelerator center, proposed searching for dark matter particles using gravitational wave detectors designed to measure faint fluctuations in the fabric of space-time, predicted for the first time. Albert Einstein
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Dark matter in waves
There are many hypotheses about the nature of dark matter particles that accumulate in large quantities to form halos in galaxies. In his new paper, published in the Journal of Cosmology and Astroparticle Physics in December 2023, Kim hypothesized that these particles could be extremely light, as predicted by many popular dark matter theories.
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“Ultralight particles are common in many theories beyond the Standards,” Kim told Live Science via email. He added that some of these particles are “perfect candidates” for dark matter, raising some interesting implications about how the elusive entity might behave.
“Unlike other ‘particle’ dark matter candidates, ultralight dark matter particles behave more similarly to classical [electromagnetic] waves,” Kim said.
The wave properties of dark matter can lead to unexpected behavior. In particular, recent theoretical work suggests that the density of dark matter within a galactic halo should undergo random changes, repelling entire galaxies and potentially leaving subtle clues about the structure of dark matter.
“Imagine waves in the ocean; we see that there are always ripples on the ocean surface and it develops in unpredictable ways,” Kim said. “The same thing could happen in the ultralight dark matter halo,” Kim added, and the resulting fluctuations could potentially extend to millions of times the distance between the Earth and the Sun.
If dark matter is very light and actually behaves like a wave, then scientists could potentially 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 small change allows scientists to detect the presence of the gravitational wave.
In his work, Kim suggests that this distance could be changed not only by a gravitational wave but also by a moving dark matter ripple; This fluctuation will be able to attract mirrors with its gravitational field, just as it attracts celestial bodies moving around the Earth.
“These fluctuations move randomly within the solar system and constantly bombard gravitational wave detectors,” Kim said.
To see whether modern gravitational wave detectors could theoretically detect the influence of ultralight dark matter, Kim calculated how dark matter particles of different sizes might distort spacetime. Kim had to investigate a wide variety of masses, from about 16 to 28 times smaller than the mass of an electron.
His theoretical analysis showed that for all these masses, existing detectors such as the Laser Interferometer Gravitational Wave Observatory (LIGO), which helped prove the existence of gravitational waves in 2015, would not be able to detect dark matter fluctuations because their sensitivity was too great. Low.
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However, there are several projects for future gravitational wave detectors to be deployed in space, and the distance between their satellites will be about a million times larger, rather than a few miles like the distance between LIGO’s mirrors. If this distance changes even by a very small rate, the magnitude of the change should be so large that the effect of dark matter should be measurable.
“What I found is that bombardment by dark matter fluctuations can leave a distinct signal in gravitational wave detectors, and potentially future space-borne detectors could test the ultralight dark matter hypothesis,” Kim said. “My proposal uses future spaceborne gravitational wave detectors such as the Laser Interferometer Space Antenna (LISA).”
Since LISA is currently scheduled to launch in the mid-2030s, this theory may be more than a decade away from being testable. However, Kim added that in the meantime, there may be other ways to detect the effect of dark matter on space-time.
“I’m currently investigating the possibility of rapidly rotating neutron stars as another way to investigate such fluctuations,” he said.