Giant Cosmic Cotton Ball: A Dark Matter Deficient Galaxy


This deep  Hubble Space Telescope image reveals the diffuse dwarf galaxy NGC2052-DF2, an unusual “see-through” galaxy. The giant cosmic cotton ball is so diffuse and its ancient stars so spread out that distant galaxies in the background can be seen through it. Astronomers measured the luminosities of faint stars at the tip of the red giant branch in this galaxy to improve the accuracy of its distance and to conclude that, in agreement with earlier studies, it does appear to be very deficient in dark matter. Credit: Science: NASA, ESA, STScI, Zili Shen (Yale), Pieter van Dokkum (Yale), Shany Danieli (IAS) Image Processing: Alyssa Pagan (STScI)

The galaxy NGC 1052-DF2 resides in a field of galaxies about sixty-five million light-years away. Its low mass, only about two hundred million solar-masses, makes it a “dwarf” and its size, about fifteen thousand light-years in diameter, places it in the regime of ultra-diffuse galaxies. It is also distinguished by hosting a large population of luminous globular clusters.

Two years ago a second, similar faint dwarf galaxy was found near it, and the relative motions of these two galaxies strongly suggest they have very little or no dark matter; for comparison, in the

DOI: 10.3847/2041-8213/ac0335