Astronomers Discover a Transparent, Seemingly Impossible Galaxy Without Dark Matter In It

Wednesday, 28 March 2018 - 6:36PM
Space
Astronomy
Wednesday, 28 March 2018 - 6:36PM
Astronomers Discover a Transparent, Seemingly Impossible Galaxy Without Dark Matter In It
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YouTube/NASA Goddard
Despite how little we know about dark matter, we can tell when it's there, from the way it impacts galaxies and causes strange movements that don't fit the laws of gravity. Which means we can also tell when it's not there.

For the first time, astronomers using the Dragonfly Telephoto Array in New Mexico (and eventually the Hubble Space Telescope) discovered a distant galaxy with 400 times less dark matter than expected, which came as a surprise considering that most models of how galaxies form always include large amounts of dark matter. The research was just published in Nature.

This galaxy, NGC 1052-DF2, is the size of the Milky Way but only has 1/200 the amount of stars, with no dense center or spiral arms or black hole. And it was also mostly transparent, with other galaxies visible behind it.



"Now wait," you may be thinking, "how does a lack of dark matter make a galaxy transparent when the substance is invisible?" The answer calls back to why scientists thought galaxies needed dark matter to form: dark matter serves as a "scaffolding" for early galaxies, slowly accumulating as other visible matter like stars and gasses cluster around it. The result is typically the spiral arms or gaseous discs you can see in other galaxies.

Without dark matter, there's very little connecting the galaxy together, making it look faint like this oddball NGC 1052-DF2. And by examining the galaxy's unusually bright globular clusters (a compact group of stars), the researchers could see just how diffuse the galaxy was, and were able to determine the galaxy's unusually small mass.

According to Pieter van Dokkum of Yale University, the lead author of the new research, who said the following in a press release from NASA

Opening quote
"We thought that every galaxy had dark matter and that dark matter is how a galaxy begins. This invisible, mysterious substance is the most dominant aspect of any galaxy. So finding a galaxy without it is unexpected. It challenges the standard ideas of how we think galaxies work, and it shows that dark matter is real: it has its own separate existence apart from other components of galaxies. This result also suggests that there may be more than one way to form a galaxy."
Closing quote




Even though we can't see it, dark matter makes up close to 85% of all matter on the universe, all while being completely undetectable on any spectrum we have access to - with the result being that we have to detect the impact it leaves on galaxies. 

It's thought that NGC 1052-DF2 may have been formed by fragmenting off from another galaxy, but more research will need to be done. After all, if there's one of these dark matter starved galaxies out there, then there's surely more.
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