Scientists Perplexed by Galaxy Without Dark Matter

Galaxy (UDG) NGC1052-DF2 (DF2) has now been confirmed to lack dark matter.
Loukia Papadopoulos

Dark matter is believed to be a form of matter thought to account for approximately 85% of the matter in the universe and about 27% of its total mass-energy density. In fact, conceiving of a universe without dark matter would seem nearly impossible and yet the Hubble Telescope has spotted yet another such galaxy: (UDG) NGC1052-DF2 (DF2).

An international team of researchers led by Zili Shen and Pieter van Dokkum of Yale University and Shany Danieli, a NASA Hubble Fellow at the Institute for Advanced Study, measured the distance of DF2 and found it to be 22.1 +/-1.2 megaparsecs proving beyond a shadow of a doubt that the galaxy lacks dark matter. 

The new study improves on results published in 2019, based on 12 Hubble orbits and TRGB analysis, that confirmed that another neighboring galaxy UDG NGC1052-DF4 (DF4) also lacked dark matter. 

“Determining an accurate distance to DF2 has been key in supporting our earlier results,” stated Danieli. “The new measurement reported in this study has crucial implications for estimating the physical properties of the galaxy, thus confirming its lack of dark matter.”

“We went out on a limb with our initial Hubble observations of this galaxy in 2018,” van Dokkum said. “I think people were right to question it because it’s such an unusual result. It would be nice if there were a simple explanation, like a wrong distance. But I think it’s more fun and more interesting if it actually is a weird galaxy.”

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Ultra diffuse galaxies

DF2 and DF4 were also found to be comparable in size to the Milky Way galaxy. However, their total masses were only about one percent of the Milky Way’s mass, an indication of their ultra-diffuse nature.

“There’s a saying that extraordinary claims require extraordinary evidence, and the new distance measurement strongly supports our previous finding that DF2 is missing dark matter,” stated Shen. “Now it’s time to move beyond the distance debate and focus on how such galaxies came to exist.”

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