DF2 and the Case of the Missing Dark Matter

Missing dark matter in the galaxy NGC-1052-DF2 presents a problem. Galaxies should all possess dark matter. Why didn’t anyone tell DF2?

The ultra-diffuse galaxy DF2 appears to be nearly free of dark matter, thought to be found in all galaxies. Image credit: NASA, ESA, and P. van Dokkum (Yale University)

It cannot be seen by any instrument, but dark matter is thought to be found in all galaxies, binding their stars together into stellar families. Groups of galaxies are bound together by this invisible — something — apparent only from the motions of stars.

Dark matter is the “invisible glue” that holds galaxies — as well as these groups of stars — together. Galaxies are thought to form within these haloes of invisible dark matter.

So — how could astronomers have found a galaxy that appears nearly devoid of dark matter?

The Wackadoodle Galaxy

In 2018, researchers reported finding an odd galaxy — NGC 1052-DF2 (or just DF2 to its friends) — which seemed to be devoid of dark matter. This finding contradicted most conventional thinking about the formation and evolution of galaxies.

Data from the Hubble Space Telescope helps confirm the galaxy NGC1052-DF2 has little to no dark matter. Image credit: NASA, ESA, Z. Shen and P. van Dokkum (Yale University), and S. Danieli (Institute for Advanced Study)

A team of astronomers led by Pieter van Dokkum and Zili Shen of Yale University together with Shany Danieli from the Institute for Advanced Study, carried…