This large, fuzzy-looking galaxy is so diffuse that astronomers call it a “see-through” galaxy because they can clearly see distant galaxies behind it. The ghostly object, catalogued as NGC 1052-DF2, is one of only a few candidate galaxies, along with nearby NGC 1052-DF4, to perhaps have no dark matter at all. (NASA, ESA, AND P. VAN DOKKUM (YALE UNIVERSITY))

The First Galaxy Without Dark Matter Is About To Be Torn Apart

A cosmic puzzle is finally solved, as new observations answer the question of why this galaxy exists at all.

For the last couple of years, astronomy has had a tremendous puzzle to reckon with. When you look at all the large-scale structures out there in the Universe — large galaxies, galaxy groups and clusters, the vast cosmic web and even the all-sky radiation left over from the Big Bang — the same universal picture emerges. In addition to all the normal matter made of Standard Model particles in all their forms, an additional source of invisible mass is required: dark matter. Everywhere we look, on all these large scales, the same 5-to-1 ratio of dark-to-normal matter adequately explains every one of our observations.

But on small scales, the story should be quite different. All the different forces and effects should create two populations of small galaxies: ones with enormous amounts of dark matter relative to their normal matter, which should persist for long periods of time, and ones with very little relative dark matter, which should be destroyed on short cosmic timescales. Yet one galaxy, NGC 1052-DF4 (called DF4 for short), has complicated matters tremendously, as it appears to have no dark matter but hasn’t formed new stars in some…