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Ancient Black Holes May Answer The Dark Matter Riddle

Dark matter remains a mystery of modern cosmology. Something unseen in the universe is exerting gravity, affecting how galaxies spin and ensuring that whole clusters of galaxies don’t drift apart. It’s widely accepted that dark matter exists and that, like normal matter, it has mass. Unlike normal matter, however, it is invisible, or “dark.” Most scientists favor the theory that dark matter is made up of particles like visible matter, but every attempt to directly detect or even conclusively characterize those particles has proven unsuccessful.

But now a startling new theory posits that, rather than comprising new, exotic particles, dark matter is actually made up of black holes. “Studies are providing increasingly sensitive results, slowly shrinking the box of parameters where dark matter particles can hide,” said Alexander Kashlinsky, an astrophysicist at NASA’s Goddard Space Flight Center. “The failure to find them has led to renewed interest in studying how well primordial black holes – black holes formed in the universe’s first fraction of a second – could work as dark matter.”

Left: This infrared image from NASA’s Spitzer Space Telescope of a sky area in the constellation Ursa Major. Right: After masking out all known stars and galaxies to enhance what’s left, an irregular background glow appears. Credit: NASA

Setting Sights on Dark Matter

Kashlinsky had the idea that primordial black holes could be responsible for the effects of dark matter in 2005, while examining data from NASA’s Spitzer Space Telescope. He and his team were studying the cosmic infrared background, a low-level glow that permeates the universe. This light was irregular and patchy, with more bright spots than could be explained by distant galaxies. In 2013, another study at NASA’s Chandra X-ray Observatory showed similar patchiness in the cosmic x-ray background (the pervasive field of ancient x-rays) in the same spots. Kashlinksy believes the only objects that could plausibly have caused that level of patchiness across the spectrum of light are black holes.

NASA has several continuing projects to study the nature and origin of dark matter. Among them are the Fermi Gamma-ray Space Telescope, which observes high-energy light from the center of our galaxy, and the Alpha Magnetic Spectrometer, which detects cosmic ray particles from the outside of the International Space Station. According to Kashlinsky, “This study is an effort to bring together a broad set of ideas and observations to test how well

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  • Leah Crane is a Chicago-based freelance science writer and editor primarily covering physics and space. She really, ​*really*​ loves space and tweets about it at @DownHereOnEarth. She holds a BA in Physics from Carleton College and is currently working as an editorial intern at SpaceNews while seeking continuing employment in science communication.

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