Earth may be swimming in an ocean of dark matter, according to new theoretical research. Waves in that invisible ocean, lapping against our planet’s upper atmosphere, may generate detectable radio waves that could finally help us find this elusive part of the universe.
A wealth of astrophysical and cosmological evidence points to the existence of dark matter, from the unexplained rotation curves of certain galaxies to the growth of the largest structures in the universe. Attempts to explain this wide variety of observations with alternative formulations of gravity have failed, so the vast majority of astronomers think that dark matter is an unknown form of matter that only rarely interacts with light or normal matter.
But that’s a very broad idea that covers a lot of possibilities. Dark matter may consist of solid particlesbut the searches for such particles have largely turned up nothing. An interesting alternative, then, is that dark matter is exceptionally light, either in the form of theoretical particles known as “axions” or as an exotic form of photon that carries a bit of mass.
With such incredible lightness — millions of times lighter than the lightest known particles — dark matter could behave in very strange ways. In particular, instead of appearing as individual point-like bullets, the dark matter could behave more like large waves that splash through the cosmos.
In a recent research Published on the preprint server arXiv, physicists examined models of ultra-luminous dark matter that wasn’t completely dark, allowing it to interact with normal matter extremely rarely. Most of the time, these interactions barely registered, producing nothing detectable. But on rare occasions, the dark matter and normal matter interacted enough to produce a significant amount Radio waves.
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This would happen if the dark matter were a plasma and when the frequency of dark matter waves matched the frequency of plasma waves. When this happened, a resonance would occur, strengthening the interaction and producing radiation in the form of radio waves, the team’s models suggested.
The universe is no stranger to plasmas — all stars spew plasma into space in the form of stellar winds — so theorists had already studied the production of radio waves by dark matter interacting with environments like the solar corona or the interstellar medium. But in this new study, the scientists discovered an interaction point much closer to home: our planet’s ionosphere.
Earth’s ionosphere is the thin, hot layer of the upper atmosphere, made up of a loose collection of ionized (charged) particles — a plasma. Waves naturally slosh through it, and the researchers found that these waves can interact with waves of hypothetical dark matter that could be washing over Earth.
The radio waves produced by this interaction would be barely detectable. But the researchers found that they could potentially detect these waves by using a carefully tuned radio antenna to search for a specific frequency of radio waves for a year.
This idea is particularly promising because Earth’s ionosphere offers several advantages over other sources of dark matter-produced radio waves. First, the ionosphere naturally reflects many radio waves from deep space, making it relatively free of contaminating signals. Second, the ionosphere is directly above us, easily accessible, and is already being constantly monitored and studied.
It’s a long shot. This form of dark matter is highly theoretical, and it would take years, if not decades, to perfect the observational techniques to search for these radio waves. But if it works, it would be a goldmine, allowing us to study one of the most mysterious elements in the universe, right on our cosmic doorstep.