Aug 28, 2016 I Brett Tingley

Mysterious ‘Dark’ Galaxy Is 99% Dark Matter

As the search for dark matter on Earth marches on with little results, astronomers are looking into deep space for signs of the elusive dark form of matter. It’s estimated that dark matter makes up around 27% of the mass of the universe, yet searches for evidence of dark matter on Earth have yet to produce any results. Luckily for dark matter enthusiasts, an international team of astronomers has discovered a galaxy composed entirely of dark matter. This ‘dark’ galaxy is known as Dragonfly 44, and lies in nearby space close to the Coma Berenices constellation.

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Dragonfly 44, the 'dark' galaxy.

According to the researchers’ recent publication in Astrophysical Journal Letters, the galaxy is what’s known as an ultra-diffuse galaxy, meaning the galaxy has a very low concentration of stars for its size. With fewer stars to hold the galaxy together, the stars that do exist in the galaxy must have very high masses. Due to the low luminosity emitted from the galaxy, researchers concluded that the galaxy must have an abnormally high dark matter content:

The apparent survival of these ultra-diffuse galaxies (UDGs) in a rich cluster suggests that they have very high masses. Our results add to other recent evidence that many UDGs are "failed" galaxies, with the sizes, dark matter content, and globular cluster systems of much more luminous objects.

Dragonfly 44 has a galactic mass close 1 trillion times the mass of our Sun, close to the mass of the Milky Way galaxy. However, only .01% of the galaxy’s mass is in the form of stars or other ‘light’ matter; the other 99.99% is assumed to likely be dark matter.

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Dark matter can be seen here by the gravitational disruption it creates on other stars' light.

Pieter van Dokkum, lead author of this study and Yale professor of astronomy and physics, told the discovery of high concentrations of dark matter in Dragonfly 44 could potentially lead to a greater understanding of dark matter or even discovery of dark matter itself, now that researchers know what type of signals to look for:

Ultimately what we really want to learn is what dark matter is. 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.

Recent discoveries by physicists have lent strong evidence for the existence of dark matter or even an as yet unknown force of nature. Soon, our current understanding of the universe might be as laughable to future generations as geocentrism is to us today. C’est la science!

Brett Tingley

Brett Tingley is a writer and musician living in the ancient Appalachian mountains.

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