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SCIENCE: NASA, ESA, STSCI, ZILI SHEN (YALE), PIETER VAN DOKKUM (YALE), SHANY DANIELI (IAS) IMAGE PROCESSING: ALYSSA PAGAN (STSCI)
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By Victoria Jaggard
Imagine you met someone who was walking and going about their life—and then you found out they had no bones. That’s essentially the mystery astronomers are trying to solve with a pair of galaxies called DF2 and DF4. By most accounts, these dim, puffy collections of stars should not exist—because neither of them has any dark matter.
Scientists in the late 1960s figured out that dark matter acts as a kind of gravitational glue, keeping stars on the edges of whirling galaxies from flying off into space. Since then, evidence has accumulated that dark matter is also a larger cosmic scaffolding, helping matter clump into stars, stars gather into galaxies, and galaxies converge into clusters. So when Yale’s Pieter van Dokkum found galaxies without this essential ingredient, he knew he’d stumbled on a massive mystery.
Now, using data from the Hubble Space Telescope to run new computer simulations, van Dokkum and his colleagues think they may have cracked the case: These oddities are the remnants of a high-speed collision between two much larger galaxies. When the two giants smashed into each other, they say, their dark matter kept on flying while their visible matter ended up in a hot, high-pressure heap, ultimately forming a string of smaller dark matter-deficient galaxies. As Nadia Drake reports, the notion has divided astronomers. But if it can be confirmed, their work might help scientists understand fundamental properties of dark matter itself.
Read the full story here. (Pictured above, the unusual “see-through” galaxy viewed by the Hubble Space Telescope.)
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