Earth may be swimming through an ocean of dark matter—and waves in that invisible ocean swirling against our planet’s upper atmosphere may generate detectable radio waves that allow us to finally find this elusive component of matter. universe, according to new theoretical research.
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 rarely interacts with light or normal matter.
But this is a very broad idea that encompasses many possibilities. Dark matter may consist of massive particles, but searches for those kinds of particles have largely come up empty. So an intriguing alternative is that dark matter is extremely light, either in the form of theoretical particles known as “stocks” or as an exotic form of photon that carries little mass.
With that incredible lightness—millions of times lighter than the lightest particles known—dark matter can act in very strange ways. In particular, instead of appearing as individual point-like blobs, dark matter would appear behave more like large waves that swings around the cosmos.
In one recent study published on the arXiv preprint server, physicists explored models of ultralight dark matter that was not completely dark, allowing it to interact extremely rarely with normal matter. Most of the time, these interactions barely register, producing nothing discernible. But in rare cases, dark matter and normal matter interacted enough to produce a significant amount radio waves.
Connected: Evidence of dark matter? The mysterious substance may be interacting with itself in the nearby galaxy
This would happen when dark matter collides with a plasma and when the frequency of dark matter waves aligns with the frequency of plasma waves. When that happened, a resonance would occur, amplifying 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 eject plasma into space in the form of the stellar wind – so theorists had already explored the production of radio waves due to dark matter interacting with environments such as the solar corona or the interstellar medium. But in this new research, scientists discovered an interaction point much closer to home: our planet’s ionosphere.
The Earth’s ionosphere is the thin, hot layer of the upper atmosphere and consists of a loose collection of ionized (charged) particles – a plasma. Of course there are waves going through it, and the researchers found that those waves could interact with hypothetical dark matter waves that could wash over the Earth.
The radio waves produced by this interaction would be barely detectable. But the researchers found that by using a radio antenna carefully tuned to look for a specific frequency of radio waves over the course of a year, they may be able to detect these waves.
This idea is particularly promising because the Earth’s ionosphere offers several advantages over other sources of radio waves produced by dark matter. First, the ionosphere naturally reflects many radio waves from deeper space, making it relatively free of contaminating signals. Second, the ionosphere is right above us, easy to access and already the subject of constant monitoring and study.
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 technique to look 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.