# New observation of a Galaxy without dark matter: what is(are) the implication(s)?

This recent paper in Nature (also see here$^1$) claimed to have discovered a galaxy without dark matter. However, in the Standard paradigm of cosmology dark matter played a crucial role in the formation of galaxies. What does this discovery, say about the nature and existence of dark matter? Does it rule out how we explain the galaxy rotation curves?

$^1$The video link that I've cited says that this lack of dark matter in a galaxy strengthens the existence of dark matter though I don't understand why.

• As any result, it can mean anything and its contrary. People who don't believe in the existence of dark matter will see another refutation, while people who strongly believes in the existence of dark matter are going to complexify their models in order to account for this possibility, by introducing new complicated interaction terms, new free parameters, and other ad-hoc explanations. – sure Apr 1 '18 at 12:43
• Since dark and baryonic matter are flowing somewhat independently yet attract, the observation doesn't tell much more than observing a dark matter halo with little baryonic matter inside (which, I seem to recall, has been observed through gravitational lensing). – Anders Sandberg Apr 1 '18 at 12:50
• It occurred to me when I heard of this that a bullet-cluster like event early on and involving enough baryonic dust and gas could nucleate a low-dark matter galaxy. Maybe. If the figures work out. – dmckee --- ex-moderator kitten Apr 1 '18 at 16:30
• @sure haven't you got this backwards? This observation, if anything, strongly supports Dark Matter, since the alternative explanations involve fundamental properties of nature / gravity, which can't be simply "turned off" for a single gravity, while technically there could be good reasons for the dark matter halo to not be present. – Prof. Legolasov Apr 1 '18 at 17:20
• @SolenodonParadoxus: which alternatives? I don't know any good alternatives, but that doesn't mean that this kind of evidences is not supporting your will to dismiss dark matter as a good explanation, thus motiving the search for alternatives. – sure Apr 1 '18 at 19:00