In one minute

Lasha Berezhiani and Justin Khoury propose dark matter superfluidity, which matches the cosmological successes of the standard ΛCDM model while reproducing MOND behaviour in galaxies. Dark matter is made of strongly self-interacting axion-like particles of about an electronvolt, forming a superfluid core in galaxies. Superfluid phonons follow a MOND-like effective action and mediate MOND-like acceleration between ordinary matter particles. It separates galaxies, where MOND works, from clusters, where hotter dark matter is partly or fully in the normal phase. Testable signatures include vortices in galaxies, merger dynamics set by infall speed versus phonon sound speed, and separate mass peaks in bullet-like cluster mergers.

Theory of dark matter superfluidity