Are Magnons a Telltale Sign of Dark Matter?

James Maynard
Jun 18, 2020 · 4 min read

Might dark matter be found here on Earth? A new study suggests a new idea for one of the greatest mysteries in science

Dark matter is one of the greatest mysteries in astronomy and physics today, spurring both theoretical and observational research. No matter where astronomers look, star clusters and galaxies are bound together with far more gravitational pull than can be accounted for from the stars and other matter seen in these systems. The two most popular ideas of where this gravity stems from include ordinary diffuse matter (MACHOs), or undiscovered subatomic particles (WIMPs). Yet, both these ideas are challenged by observations.

Magnons — tiny particles smaller than any so far predicted by theories of WIMP — could be the telltale sign showing dark matter as a particle, a new study suggests. Such a particle could be found in a “hidden sector” of particles, much lighter than the masses being searched for in past studies.

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A ring of dark matter holds together this cluster of galaxies, seen in by the Hubble Space Telescope. NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)

Previous searches for weakly interacting massive particles (WIMPs) focused exclusively on particles far more than predicted for magnons. Researchers searching for WIMP’s typically utilize large detectors, such as the XENON detector in Italy, containing 70,000 gallons of water.

“Dark matter is always flowing through us, even in this room. As we move around the center of the galaxy, this steady wind of dark matter mostly goes unnoticed. But we can still take advantage of that source of dark matter, and design new ways to look for rare interactions between the dark matter wind and the detector,” said Dr. Kathryn Zurek, professor of theoretical physics at Caltech.

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Particles of dark matter could affect electrons in such away as to give away the presence of the invisible “something” that makes up most of the matter in the Universe, a new study suggests. Image credit: Caltech/ Zhengkang “Kevin” Zhang

It is difficult to detect dark matter particles directly, but they might strike electrons, altering the spin of the particle, and producing magnons, the new study, published in Physical Review Letters, suggests.

Magnons are thought to be quasiparticles — a name given to a solid acting as if it contained WIMPs. These spin of these particles (acting like tiny magnets) can become excited as groups.

Small, tabletop-sized detectors (stored underground) could be used to find these magnons, researchers state. A magnetized crystallized material could detect the presence of magnons produced by dark matter. Conducting the experiments well underground and cooling the detectors could shield the detectors, allowing researchers to see the effects of magnons.

“You go, dark energy! Go on, dark matter. They don’t understand you, dark matter. They don’t get you.”
— Larry Wilmore

If such an experiment were ever conducted, researchers believe they would see the number of magnons produced waver over the course of each day. The particles within such a detector would tend to be aligned in one direction, meaning that the number of particles detected would depend on the angle at which they strike dark matter. As this angle changes over the course of each day, so would the number of magnons found by such a machine.

Neil deGrasse Tyson explains what we know about dark matter. Video credit: Business Insider

“”During the day, for example, you may have a higher detection rate when the dark matter comes from above than from the side. If you saw that, it would be pretty spectacular and a very strong indication that you were seeing dark matter,” said Zhengkang (Kevin) Zhang, a postdoctoral scholar at Caltech.

Researchers on the study also proposed other unique means of detecting dark matter, including looking for a different quasiparticle, phonons, produced by vibrations in a crystal lattice.

Dark matter was first proposed in the 1930’s by astronomer Fritz Zwicky, in an effort to explain why clusters of galaxies do not fly apart. Four decades later, Vera Rubin and Kent Ford found the first evidence for dark matter within galaxies. Today, we know this dark matter — which emits no radiation — makes up 80 percent of the matter in the Universe.

“We’re looking into new ways to look for dark matter because, given how little we know about dark matter, it’s worth considering all the possibilities,” said Zhang.

James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.

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