Found: Dragonfly 44, a strange galaxy made mostly of dark matter

A galaxy called Dragonfly 44 has caught scientists’ attention for a fascinating reason: it’s made almost completely of dark matter.

Astronomers used two telescopes on Maunakea, Hawaii to study the dim galaxy, and by measuring the velocities of the stars in it, they calculated its mass. While Dragonfly 44 has about the same mass as the Milky Way, it has fewer than a hundredth the number of stars.

All told, the strange galaxy is 99.9 percent dark matter— only a tiny bit of it is considered to be typical matter, like stars and other objects visible to light. Astronomer estimate that Dragonfly 44 is about a trillion times as massive as our own sun.

“Ultimately what we really want to learn is what dark matter is,” Pieter van Dokkum, the first author of the study reporting the finding, and a professor of astronomy at Yale University, said in a statement. “The race is on to find massive dark galaxies that are even closer to us than Dragonfly 44, so we can look for feeble signals that may reveal a dark matter particle.”


Jeremiah Ostriker, a professor of astronomy at Columbia University and an expert in dark matter, called the find “a very important discovery” and a “coup.”

“There are many low mass galaxies which are dominated by dark matter, but for most normal galaxies like the Milky Way, normal stars dominate in the inner parts and dark matter is prominent in the 'halo' surrounding the system,” he told in an email. “This galaxy is unique in that it is massive, nearby and dark matter dominated throughout. We will have a chance to study it carefully and perhaps find clues as to the nature of the dark matter.”

Dark matter is an enigma. David Kipping, an assistant professor of astronomy at Columbia University, explained in an email to that dark matter “exerts a gravitational influence” but is “transparant to light.”

And van Dokkum, the study’s lead author, described it as “a mysterious form of matter that is invisible but is thought to make up most of the mass in the Universe” in an email to

The study will be published in the journal Astrophysical Journal Letters.

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