Dark Matter is Complicated

The fact that we have found gravitational waves tells us that we have come a long way in terms of science and technology.  We detected a perturbation in the fabric of space-time that was one one-thousandth the diameter of a proton.  It’s insane to think about that level of precision.  And yet we still can’t find Dark Matter, the stuff that is literally everywhere in the universe.  Is it our problem? Or is dark matter just on a whole different level?

Credit: Credits to Aurore Simonnet, Sonoma State University (for the active galaxy core) and to NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring (for image of earth).

By now, we know that dark matter isn’t some clump of stuff sitting out there in space.  But that doesn’t mean we know what it is either.  When it comes to solving a difficult scientific mystery, narrowing your field can be more important than trying to solve the whole mystery.  Researchers are not only trying to identify dark matter, they are trying to identify what dark matter can’t be.  When looking for dark matter, the best places are the centers of galaxy clusters, which host the largest density of it.

A possibility for dark matter is that is it made from extremely light particles that have one-billionth the mass of the electron, called Axon-like particles (ALPs).  If they make up the dark matter we see, there would have to be an astronomical number of them (literally).  For the first time, researchers have used NASA’s gamma-ray telescope on the Fermi satellite to study light from the central galaxy of the Perseus galaxy cluster in the hunt for ALPs.

Even though the results haven’t given us an answer yet, the sensitivity of the instrument has allowed scientists to rule out certain types of ALPs, narrowing the search for dark matter.  The problem with ALPs, and with dark matter in general, is that it doesn’t interact with anything.  However, ALPs may temporarily become photons when passing through a magnetic field, allowing telescopes like Fermi to find evidence of their existence.

“The ALPs we have been able to exclude could explain a certain amount of dark matter. What is particularly interesting is that with our analysis we are reaching a sensitivity that we thought could only be obtained with dedicated future experiments on Earth,” says Manuel Meyer, post-doc at the Department of Physics, Stockholm University.

There is no easy answer to the dark matter puzzle, but the focus is narrowing, and we are making progress, even if it is slow.

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