Hubble captures a galaxy that’s chock-full of dark matter

By Georgina Torbet September 21, 2020

The newest image from the Hubble Space Telescope shows a galaxy that’s more than it appears. While NGC 5585 may look on the surface like a normal spiral galaxy, it’s thought to be chock full of dark matter.

Located in the constellation of Ursa Major, sitting of the tail of the great bear, this galaxy is in many ways a typical spiral galaxy. You can see areas where new stars are being born, shining in a bright blue, though the galaxy doesn’t have much of a central bulge so its shape appears diffuse.

Resting on the tail of the Great Bear in the constellation of Ursa Major, lies NGC 5585, a spiral galaxy that is more than it appears shown in this image captured by the Hubble Space Telescope. — Resting on the tail of the Great Bear in the constellation of Ursa Major, lies NGC 5585, a spiral galaxy that is more than it appears shown in this image captured by the Hubble Space Telescope. ESA/Hubble & NASA, R. Tully; Acknowledgement: Gagandeep Anand

The real oddity about this galaxy, though, is its composition. The stars, dust, and gas that make up this galaxy account for only a small fraction of its total mass, meaning that it must contain more dark matter than other similar galaxies.

“The stellar disc of the galaxy extends over 35,000 light-years across,” the Hubble scientists write in a blog post. “When compared with galaxies of a similar shape and size, NGC 5585 stands out by having a notably different composition: Contributing to the total mass of the galaxy, it contains a far higher proportion of dark matter.”

Dark matter is the name given to a theoretical type of matter which makes up around 85% of the matter in the universe. When astronomers observe the universe, they see that galaxies ought to be torn apart because they don’t appear to have enough mass to produce sufficient gravity to hold themselves together. But that’s not what happens.

So they theorize that there must be some amount of mass that we can’t see in galaxies, holding them together. They named this unseen mass dark matter. The problem when trying to understand this phenomenon is that dark matter doesn’t emit, absorb, or reflect light. That makes it extremely difficult to observe, so we have to look for indirect evidence of its presence.

There’s still so much we don’t know about dark matter, which is why it’s important to study oddities like galaxy NGC 5585, so we can learn more about this mysterious type of matter and how it affects galaxies throughout the universe.

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Georgina Torbet

Space Writer

Georgina is the Digital Trends space writer, covering human space exploration, planetary science, and cosmology. She…

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