astronomers find more dark matter free galaxies

A new study sees evidence of more than a dozen galaxies that seem to lack dark matter and raises big questions about our ideas of galaxy formation.
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Just in case you thought cosmologists moved any closer to understanding dark matter over the last year, prepare to be disappointed. While a proposed discovery claimed to find two galaxies that lacked dark matter, which implies that dark matter is made of particles rather than being a fluke to gravity on vast scales, the results were quickly put in doubt by a second look at these objects. Another team found that those galaxies were in fact chock of dark matter, it’s just that their distances from us were incorrectly measured. Now, yet another group of astronomers are ready to reignite the debate after finding 19 more galaxies apparently lacking dark matter and giving more ammo to scientists who argue that dark matter is really a substance.

Unfortunately, this finding, even if correct, doesn’t actually clear anything up. If anything, it just raises more questions. First and foremost, there’s a good chance that future measurements of these galaxies will show the presence of dark matter once again. Secondly, even if they’re truly devoid of dark matter, just 19 galaxies out of millions still can’t explain much about the makeup and behavior of dark matter, which still saturates a quarter of the universe as far as we know in all the observations and models replicated time and time again. And finally, even if we accept that dark matter is a substance made of particles, we have absolutely no idea what it could be and have ruled out pretty much every viable candidate for its composition.

It’s a frustrating conundrum. On the one hand, we know it’s out there and our best tools built to examine the building blocks of the universe replicate its existence and behavior without us programming them to do it. On the other, we still can’t agree on what it is and none of our hunches are panning out. It’s like trying to figure out the contents of a black box we can’t pry open by shaking it and scanning it with tools that give us only partial, blurry snapshots of what’s inside. Meanwhile, when we try to build a replica filled with whatever we think should act the same way, literally nothing matches the scans and sounds of the original. At this point, it seems like we’ll need some sort of spontaneous breakthrough to make any progress in understanding what dark matter is and why it exists.

See: Guo Qi, et. al., Further evidence for a population of dark-matter-deficient dwarf galaxies, Nature Astronomy (2019), DOI: 10.1038/s41550-019-0930-9

# space // astronomy / cosmology / dark matter


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