A clumpy dark matter halo with varying densities and a very large, diffuse structure, as predicted by simulations, with the luminous part of the galaxy shown for scale. Image credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI).

Dark matter rises to its biggest challenge

And succeeds!

“Faced with the choice between changing one’s mind and proving that there is no need to do so, almost everybody gets busy on the proof.”
-J. K. Galbraith

One of the most important innovations in understanding the Universe and how it came to be the way we see it today is dark matter. This unseen, invisible form of mass helps hold the galaxies, groups and clusters in the Universe together, and enables us to form the great cosmic web of structure we see today. Last month, a new study came out showing that individual galaxies appear to rotate in a way that’s solely dependent on the normal matter (protons, neutrons and electrons) inside, without any need for dark matter. The incredible challenge it put forth was for dark matter to explain why this would be the case. Remarkably, just three weeks later, a duo of researchers have risen to the challenge, and done exactly that.

The Coma cluster of galaxies, whose galaxies move far too quickly to be accounted for by gravitation given the mass observed alone. Image credit: KuriousG of Wikimedia Commons, under a c.c.a.-s.a.-4.0 license.

Dark matter is known, from a variety of independent observations, to comprise about six times as much mass as normal matter in the Universe. Without it:

• fluctuations in the Cosmic Microwave Background wouldn’t exhibit the same patterns,