A perseid meteor, streaking across the night sky. Image credit: Andreas Möller

Meteor detection technique could be used to find dark matter particles entering the atmosphere

Researchers at Ohio State University have developed a new method for detecting dark matter, based on existing meteor detection technology. By using ground-based radar to look for ionization trails, similar to those produced by meteors as they pass through the air, they hope to use Earth’s atmosphere as a detector for large particles. The results of experiments using this technique would help researchers narrow the range of possible characteristics of dark matter particles.

The existence of dark matter is fairly well accepted by mainstream physicists. Since Lord Kelvin calculated that the mass of all the stars in the Milky Way galaxy was far less than the mass of the galaxy itself, we know that much of the matter in the Universe is beyond us. not visible. As technology improved, we learned to detect things that were hidden by visible light telescopes, but we still can’t explain all the missing matter. We call this missing matter “dark matter,” and current estimates indicate that 85% of the mass of the universe is dark matter. Most physicists now believe that dark matter is made of an as yet unknown particle.

Dr. John Beacom of Ohio State University proposed an experiment to determine the characteristics of this particle. He wants to adapt radar technology used to detect and measure meteors as they pass through the atmosphere, using it to look for similar trails that could indicate a dark matter particle colliding with air molecules. This technique uses ground-based radar stations to detect and measure ionization trails in the upper atmosphere.

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When a meteoroid enters the Earth’s atmosphere, it passes through the air faster than the air itself can move away. This causes the air in front of the meteor to compress and become so hot that it ionizes – individual air molecules collide with each other so hard that they lose electrons. Ionized air not only glows, but is opaque to radio waves. This causes radar signals to reflect back to earth, allowing meteors to be detected even during daylight hours.

Theoretical physicists have calculated the physical characteristics that dark matter particles might have. Unfortunately, since most of what we know about these particles is that they interact weakly with normal matter (so far we have only detected it through its gravitational influence), this leaves a wide range of possibilities. Dr Beacom points out that if dark matter particles are at the larger, heavier end of the range of possibilities, then they would more easily interact with “normal” matter, although such interactions are still rare.

“One of the reasons dark matter is so hard to detect could be that the particles are so massive,” Beacom said. “If the mass of dark matter is small, then the particles are common, but if the mass is large, the particles are rare.”

If these particles are large, traditional ground-based detectors may never see them because the particles are absorbed by the Earth’s atmosphere. But if that happens, then they should have enough energy to produce an ionization trail, similar to what we see with meteors. Meteor detection radar installations could therefore be adapted to also search for dark matter particles, essentially turning the entire Earth’s atmosphere into one giant particle detector.

The existence of dark matter was first predicted in 1884 by Lord Kelvin. He had calculated the mass of the Milky Way galaxy, based on the speed at which it rotates, and discovered that it must be significantly heavier than the visible stars combined. He theorized that most of the galaxy’s mass must be made up of “dark” material – things that couldn’t be seen with telescopes of the time. However, most scientists assumed this meant there would be lots of cold gas, dust, exoplanets, and other objects that don’t shine with their own light. The term “dark matter” was first used to describe these things in a French article in 1906.

abell 611 and its galaxies and dark matter
The Hubble Space Telescope offers a cosmic web of galaxies and dark matter unseen in the Abell 611 cluster. Credit: ESA/Hubble, NASA, P. Kelly, M. Postman, J. Richard, S. Allen

Many other lines of evidence have since emerged: Fritz Zwicky noticed in the 1930s that the galaxies in the Coma cluster moved as if the entire cluster were 400 times heavier than the total mass of all its visible members. Early radio astronomers in the 1960s saw that spiral galaxies were spinning far too quickly around their edges – they should just move away unless there was an additional source of gravity to hold them together. Vera Rubin, Kent Ford and Ken Freeman made the same discovery soon after, using newly improved spectrographs to measure the rotation curve of galaxies in visible light. And a series of deep cosmological observations in the 1980s detected gravitational lensing and anisotropies in cosmic microwave background radiation (CMBR), adding to the evidence for the existence of dark matter.

It should be noted that no one yet knows whether dark matter particles will actually produce these ionization trails. Detectors built using this technique may never see anything at all. But either result, detections or no detections, would be a good thing. Either way, an experiment using this detection technique will answer the question, “Are dark matter particles big, heavy, and rare?” Or are they small, light and numerous?

To learn more about this technique, read the original research paper at https://news.osu.edu/astronomers-create-new-technique-to-assist-in-search-for-dark-matter/

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