Look: Ghostly, mysterious galaxies help unlock the secrets of dark matter

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You’re probably used to the stunning images of our bright, densely-packed galaxy, the Milky Way.

But another type of galaxy, called an ultradiffuse galaxy (UDG) is the antithesis of the populated cluster we call home.

While the Milky Way is packed with stars and gas, UDGs are dim and sparse.

In 2016, researchers discovered a UDG called Dragonfly 44 that was 99 percent dark matter.

Teymoor Saifollahi and NASA/HST via Wikimedia Commons

Now, we're getting closer to unlocking the secrets of these ghostly galaxies — starting with how they formed.

Teymoor Saifollahi and NASA/HST via Wikimedia Commons

Writing on September 6 in the journal Nature Astronomy, an international team of researchers used simulated UDGs to shed light on how they come to exist.

The faint aura of light in the right-hand image is a UDG, imaged by the Hubble Space Telescope in 2019. On the left is a UDG analyzed in the recent simulation.


UDGs are sometimes called “failed Milky Ways” — implying they were on track to form enough stars to look like our own galaxy.

Some no longer produce stars, known as quenched UDGs.

It was thought previously that UDGs had to exist in clusters in order to lose their gas and stop making stars.

But, strangely enough, some have been found isolated in the universe.

The study authors say that some UDGs likely orbited larger systems at one point, but spent the bulk of their time in isolation.


It’s kind of like how Halley’s Comet flies through our solar system every 75 years, but spends most of its time isolated in space.

Thanks to the simulation, researchers say there are likely more quenched galaxies out there than we realized — up to 25 percent of all UDGs.

The actual percentage of quenched UDGs we’ve observed is much lower.

“This means a lot of dwarf galaxies lurking in the dark may have remained undetected to our telescopes.”


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