A new class of galaxy has been discovered, one made almost entirely of dark matter [View all]

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Source: Washington Post

A new class of galaxy has been discovered, one made almost entirely of dark matter

By Rachel Feltman August 25 at 1:00 PM

It's no secret that most of the universe is made of dark matter, the unknowable, as-yet-undetected stuff that barely interacts with the "normal" matter around it. In the Milky Way, dark matter outnumbers regular matter by about 5 to 1, and very tiny dwarf galaxies are known to contain even more of the stuff.

But now scientists have found something entirely new: a galaxy with the same mass as the Milky Way, but with only 1 percent of our galaxy's star power. About 99.99 percent of this other galaxy is made up of dark matter, and scientists believe it may be one of many.

The galaxy Dragonfly 44, described in a study published Thursday in the Astrophysical Journal Letters, is 300 million light years away. If scientists can track down a similar galaxy closer to home, however, they may be able to use it to make the first direct detection of dark matter.

The researchers who found Dragonfly 44 weren't looking for a dark galaxy. Another surprise: They found it using a telescope built out of camera parts. The Dragonfly Telephoto Array was built by a group of astronomers at Yale University and the University of Toronto who realized that telephoto lenses — so often used for nature photography and sporting events — were well-suited for spotting the kind of large, dim objects that pose problems for typical telescopes.

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Read more: https://www.washingtonpost.com/news/speaking-of-science/wp/2016/08/25/a-new-class-of-galaxy-has-been-discovered-one-made-almost-entirely-of-dark-matter/

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Related: A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra Diffuse Galaxy Dragonfly 44 (Astrophysical Journal Letters)

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[font size=1]Dragonfly 44 is very faint for its mass and consists almost entirely of dark matter. (Pieter van Dokkum, Roberto Abraham, Gemini Observatory/AURA)[/font]