Astronomers have followed a faint, cosmic trail of gas to a third galaxy that has no dark matter. 

In a new study in The Astrophysical Journal, a team of Yale astronomers reports on a dwarf galaxy located45 million light-years from Earth — called NGC 1052-DF9 — that appears to have formed in a straight line with nine other galaxies. 

Two of those other galaxies, DF2 and DF4, were previously shown to lack dark matter — an invisible, theorized material that gives shape to the universe and is thought by most astronomers to be essential to galaxy formation. 

Now, DF9 has joined the no-dark-matter club. 

“A line of galaxies lacking dark matter has never been seen before,” said Michael Keim, a Ph.D. student in astrophysics in Yale’s Graduate School of Arts and Sciences and first author of the new study. “The discoveryprovides some of the strongest evidence yet that these galaxies formed through an extreme and previously unseen process and offers a rare new window into the nature of dark matter itself.” 

Keim’s advisor, Yale astronomer Pieter van Dokkum, led the original studies that analyzed DF2 and DF4, using data from the Hubble Space Telescope. Van Dokkum, the Sol Goldman Family Professor of Astronomy and professor of physics in Yale’s Faculty of Arts and Sciences, is co-author of the new study. 

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