Jun 22, 2021 - Science

Missing: Dark matter from an unusual galaxy

Stars in space

The galaxy DF2 seen by the Hubble Space Telescope. Photo: NASA/ESA/STScI/Yale/IAS

Scientists have confirmed the discovery of a strange galaxy 72 million light-years from Earth that appears to be missing its dark matter.

Why it matters: It's long been thought that dark matter — the invisible stuff that makes up much of matter in the universe — is a key ingredient for galaxies, but the discovery complicates that picture.

What they found: Researchers using the Hubble Space Telescope first spotted the dark matter deficient galaxy, named NGC 1052-DF2, in 2018, but a new study in The Astrophysical Journal Letters confirmed the observation.

  • The scientists took a precise measurement of the distance to the galaxy — which is about the width of the Milky Way with 1/200th the number of stars — using the Hubble.
  • If the galaxy were closer to Earth than initially proposed, it would intrinsically be less massive, meaning it would have to have more dark matter to look the way it does, according to the researchers.
  • The new measurements, however, showed DF2 is actually farther away than scientists initially thought, at 72 million light-years instead of 65 million.

The intrigue: It's still not clear exactly how this galaxy devoid of dark matter formed, but it's not the only one.

  • Another galaxy — called NGC 1052-DF4 — studied by scientists using the Hubble appears to be low in dark matter as well, and it could have formed in the same group of galaxies as DF2.
  • DF4's dark matter, however, may have been stripped from it during an interaction with another galaxy earlier in its history, the researchers have said.
  • "So maybe there was something special in the environment where they were formed," Shany Danieli, one of the authors of the new study, said in a statement.
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