Astrophysicists propose new method to directly detect ultralight dark matter

The detection of dark matter, the elusive type of matter predicted to make up most of the universe's mass, is a long-standing goal in the field of astrophysics. As dark matter does not emit, reflect or absorb light, it cannot be observed using conventional experimental methods.

A promising dark matter candidate is so-called ultralight dark matter, which consists of particles with extremely low masses. Astrophysicists have been searching for these ultralight dark matter particles using various approaches and methods, yet they have not yet been detected.

Researchers at the University of Florida recently proposed a new method for the direct detection of ultralight dark matter particles, which is based on astrometry, the precise measurement of the positions and motions of celestial objects.

Their paper, published in Physical Review Letters, outlines an alternative approach that could be employed in future searches for these elusive particles.

"Our research emerged from a fundamental question: How can we detect dark matter if it interacts with ordinary matter only through gravity?" Sarunas Verner, co-author of the paper, told Phys.org.

"This scenario has traditionally been considered challenging for direct detection. However, building on pioneering work by Khmelnitsky and Rubakov (2014), we recognized that ultralight dark matter—with a de Broglie wavelength comparable to galactic scales—produces measurable spacetime fluctuations that could be detected through precision astrometry measurements."

Most previous searches for ultralight dark matter relied on pulsar timing arrays (i.e., collections of millisecond pulsars across the sky that are periodically observed by astronomers) as detection tools. In contrast, Verner and his colleague Jeff A. Dror explored the possibility of employing precision astrometry to probe ultralight dark matter by looking only at gravitational interactions.

"Our method leverages the fact that ultralight dark matter creates small but detectable fluctuations in spacetime itself," explained Verner.

"These fluctuations affect the apparent positions of distant celestial objects like stars and quasars. Specifically, we demonstrated that the most significant effect occurs through what astronomers call 'classical aberration'—the slight angular deflection of light from distant sources caused by the observer's motion through space."

As part of their study, the researchers calculated how these ultralight dark matter-induced spacetime ripples would impact classical aberration, making it distance-dependent. This means that nearby sources exhibit slightly different aberration than distant ones.

"These variations are extremely subtle—less than 1 microarcsecond in size—requiring highly precise astrometric measurements," said Verner. "We showed that these effects are potentially detectable with current and next-generation astrometric surveys like VLBI, Gaia, and future observatories like THEIA."

The recent study by Verner and Dror introduces an entirely new method to probe ultralight dark matter, focusing solely on gravitational interactions. Its reliance on gravitational interactions could be highly advantageous, as it could allow researchers to search for dark matter candidates that could be entirely decoupled from the Standard Model, with the only exception of gravitational laws.

"The implications of our study are substantial," said Verner. "Our method is complementary to existing probes of ultralight dark matter, including cosmic microwave background (CMB) measurements and large-scale structure (LSS) observations.

"When combined with these other datasets, precision astrometry could significantly enhance our ability to detect or constrain ultralight dark matter particles in the mass range below 10^-22 electron volts. This mass range is particularly interesting as it corresponds to particles with wavelengths on galactic scales, potentially addressing certain small-scale challenges in cosmology."

The new detection method proposed by this research group could be further developed and deployed in future searches for ultralight dark matter particles.

In their next studies, Verner and Dror are planning to extend their proposed approach, so that it can be employed to probe other sub-types of ultralight dark matter.

"Building on this foundation, we plan to extend our theoretical framework to investigate ultralight vector dark matter, which could exhibit different signatures in astrometric data," added Verner.

"We're also exploring how similar principles might be applied to probe the nature of dark energy, potentially offering new insights into the mysterious force driving cosmic acceleration."

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