The Mystery of a Newly Discovered ‘Dark Galaxy’

Oct 4, 2016

By Joshua Sokol

Among the thousand-plus galaxies in the Coma cluster, a massive clump of matter some 300 million light-years away, is at least one—and maybe a few hundred—that shouldn’t exist.

Dragonfly 44 is a dim galaxy, with one star for every hundred in our Milky Way. But it spans roughly as much space as the Milky Way. In addition, it’s heavy enough to rival our own galaxy in mass, according to results published in the Astrophysical Journal Letters at the end of August. That odd combination is crucial: Dragonfly 44 is so dark, so fluffy, and so heavy that some astronomers believe it will either force a revision of our theories of galaxy formation or help us understand the properties of dark matter, the mysterious stuff that interacts with normal matter via gravity and not much else. Or both.

The discovery came almost by accident. The astronomers Pieter van Dokkum of Yale University and Roberto Abraham of the University of Toronto were interested in testing theories of how galaxies form by searching for objects that have been invisible to even the most advanced telescopes: faint, wispy and extended objects in the sky. So their team built the Dragonfly Telephoto Array, a collection of modified Canon lenses that focus light onto commercial camera sensors. This setup cut down on any scattered light inside the system that might hide a dim object.


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2 comments on “The Mystery of a Newly Discovered ‘Dark Galaxy’

  • 1
    Pinball1970 says:

    It would be good if Krauss brought out another Quintessence to pull of these pieces of information together.

    Dark matter/energy the energy of empty space, refinements on the CMBR measurements and now gravitational waves.

    Throw in some data from the LHC too.

    “A universe from nothing” is now fours old and a lot has happened since then.



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  • @OP – Dragonfly 44 is a dim galaxy, with one star for every hundred in our Milky Way. But it spans roughly as much space as the Milky Way. In addition, it’s heavy enough to rival our own galaxy in mass, according to results published in the Astrophysical Journal Letters at the end of August.

    We should remember that all galaxies are “dark” in areas lacking the gravitational disturbances to trigger star formation – such as between the lit-up spiral arms of the Milky Way!

    http://hubblesite.org/reference_desk/faq/answer.php.id=39&cat=galaxies

    The disk is a flattened region that surrounds the bulge in a spiral galaxy. The disk is shaped like a pancake. The Milky Way’s disk is 100,000 light years across and 1,000 light years thick. It contains mostly young stars, gas and dust, which are concentrated in spiral arms. Some old stars are also present.

    Stars come in a variety of types. Blue stars, which are very hot, tend to have shorter lifetimes than red stars, which are cooler. Regions of galaxies where stars are currently forming are therefore bluer than regions where there has been no recent star formation. Spiral galaxies seem to have a lot of gas and dust, while elliptical galaxies have very little gas or dust.



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