Enlarge / The slightly hazy, light patch in the middle of the image is the DF2 galaxy, so diffuse that other galaxies are clearly visible behind it. (credit: NASA, ESA, and P. van Dokkum)
The first evidence for dark matter were galaxies that behaved as if they had far more matter than could be accounted for by the mass of their stars. Since then, we've found many other indications that the Universe is swimming with matter that we can only infer from its gravitational effect. And the original evidence that dark matter structures galaxies continued to hold.
Until that awkward moment in 2018 when we appeared to discover the existence of a galaxy with almost no dark matter. While there was skepticism regarding this initial finding, researchers eventually spotted a second galaxy that was very similar. Which was a problem, given that we had no idea how galaxies like this could form.
Now, researchers have announced that, while they were running a model of galaxy formation, a number of dark-matter-poor galaxies naturally popped out. And, by tracing the model back to see how those galaxies arose, the researchers are able to offer an explanation for these enigmas.
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