Dark matter — the strangest and most terrifying thing in the universe — may be nothing like we think it is. New observations by the Hubble space telescope call into question what scientists have believed for the past 80 years regarding the illusive particles, thought of as the invisible “glue” that binds the solar system together. According to a statement released today on Hubble’s website, a mysterious “dark matter core” has been discovered in the aftermath of a massive galaxy cluster collision, called Abell 520. The collision occurred over 2.4 billion light years from Earth.
In mainstream physics, the theory has gone that dark matter makes up most of the mass of our solar system — 83 percent, according to some scientists, as opposed to the 17 percent of the universe inhabited by ordinary matter, also known as everything in the world you’ve ever seen or felt. By measuring the gravitational movement of stars, galaxies, and especially enormous galaxy clusters, scientists have deduced that dark matter exists — though they have no idea what it’s made out of — and that it’s probably bound to ordinary matter. Well that all changed when scientists looked at Hubble images of the empty space where the Abell 520 collision had occurred. Normally, they would have expected to find a little dark matter hanging around after the shake-up, clinging to the leftover galaxies. Instead they discovered an immense “dark core” that defies scientific theory. The majority of the galaxies had quickly moved away in opposite directions after the collision, but their dark matter remained, a celestial question mark.
“This result is a puzzle,” said astronomer James Jee of the University of California, Davis, leader of the Hubble study, according to the statement. “Dark matter is not behaving as predicted, and it’s not obviously clear what is going on.”
Scientists have observed dark matter behave predictably before, such as after the collision of the Bullet Cluster, which tagged along with dark matter like a “dog on a leash.” However, only a half-dozen cluster collisions have ever been observed, making the Bullet Cluster’s “textbook example” of dark matter behavior less than bullet-proof.
“We know of maybe six examples of high-speed galaxy cluster collisions where the dark matter has been mapped,” Jee continued. “But the Bullet Cluster and Abell 520 are the two that show the clearest evidence of recent mergers, and they are inconsistent with each other. No single theory explains the different behavior of dark matter in those two collisions.”
Although scientists and astronomers are scrambling to come up with a theory to explain the bizarre behavior, they find their choices unsettling. “It’s pick your poison,” said team member Andisheh Mahdavi of San Francisco State University in California. Coming from an astrophysicist, that’s a bit alarming. One theory among the researchers guesses that dark matter might actually be “sticky” and somehow became attached to itself, instead of to the luminous galaxies as usual. Another possibility is that a galaxy may exist near the dark matter that Hubble simply can’t see. As one of the most important unsolved mysteries of modern physics, here’s to hoping the Hubble scientists make some progress in understanding how dark matter works, even if we still don’t know what it is.
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