'Missing' Dark Matter Leads to Questions About How Galaxies Form

A galaxy that appears to be “missing” its dark matter has led scientists to question their theories of how galaxies form and how dark matter works. 

A new study published in the March 29 issue of Nature used data from the Gemini North and W.M. Keck Observatories, the Hubble Space Telescope, and other international telescopes to determine a galaxy 65 million light-years away has almost no dark matter — far less than would have been expected, according to Phys.org.

"Finding a galaxy without dark matter is unexpected because this invisible, mysterious substance is the most dominant aspect of any galaxy," said lead author Pieter van Dokkum of Yale University, Phys.org reported. "For decades, we thought that galaxies start their lives as blobs of dark matter. After that everything else happens: gas falls into the dark matter halos, the gas turns into stars, they slowly build up, then you end up with galaxies like the Milky Way. NGC1052-DF2 challenges the standard ideas of how we think galaxies form."

Dark matter is invisible but is thought to hold galaxies together as they rotate so they don’t spin apart. The NGC1052-DF2 galaxy spins much more slowly than other observed galaxies and was found to have 400 times less dark matter than scientists expected for its size and brightness, according to Wired.

It’s possible the galaxy might have been formed by dark matter like others observed by scientists, but that something else might have caused the dark matter to exit the system, University of California, Irvine astrophysicist James Bullock said, Wired reported. Bullock theorizes that the discovered galaxy may have had its dark matter stripped away by a neighboring galaxy, which it now orbits.

The study team is now searching for other galaxies with similar absence of dark matter to see what else they can find out about dark matter, Wired reported.

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