This paper investigates the ultra-diffuse galaxies DF2 and DF4 in the NGC 1052 group, which exhibit unusual properties like large sizes, luminous globular clusters, and low velocity dispersions, suggesting a lack of dark matter. The authors propose that these galaxies formed from a high-velocity collision of gas-rich galaxies, similar to a smaller-scale version of the bullet cluster collision. They show that DF2 and DF4's current distances and velocities are consistent with their formation in such a collision about eight billion years ago. Furthermore, they identify a linear substructure of seven to eleven large, low-luminosity objects, suggesting a trail of dark-matter-free galaxies originating from this single event. The authors also identify potential remnants of the progenitor galaxies at the leading edges of this trail.

Pieter van Dokkum, Zili Shen, Michael A. Keim, Sebastian Trujillo-Gomez, Shany Danieli, Dhruba Dutta Chowdhury, Roberto Abraham, Charlie Conroy, J. M. Diederik Kruijssen, Daisuke Nagai, Aaron Romanowsky