In a new study, astronomers used data from NASA / ESA’s Hubble Space Telescope to calculate a more precise distance to an ultra-diffuse galaxy called NGC 1052-DF2 (DF2 for short). The new measure reinforces previous claims that DF2 lacks dark matter, the invisible glue that makes up most of the universe’s content.
DF2 is located in the constellation Cetus and belongs to the Group of galaxies NGC 1052.
This ultra-diffuse galaxy is roughly the size of our Milky Way galaxy, but only hosts 1/200 of the number of stars.
In 2018, a team of astronomers from the United States and Canada discovered that DF2 contains virtually no dark matter.
A year later, a second galaxy of this class, NGC 1052-DF4, was discovered in the NGC 1052 group.
To bolster their original discovery, astronomers continued their initial studies with a more robust Hubble look at DF2.
“We took our precautions with our first Hubble observations of this galaxy in 2018,” said Dr Pieter van Dokkum, an astronomer in the Department of Astronomy at Yale University.
âI think people were right to question it because it’s such an unusual result. It would be nice if there was a simple explanation, like wrong distance. But I think it’s more fun and more interesting if it’s actually a weird galaxy.
Astronomers have focused on the aging of the red giant stars on the outskirts of the DF2 galaxy which all reach the same peak in brightness as they evolve.
âThe study of the brightest red giants is a well-established distance indicator for nearby galaxies,â said Zili Shen, a graduate student in the Department of Astronomy at Yale University.
âThe new Hubble observations help us confirm that DF2 is not only further from Earth than some astronomers suggest, but also slightly further away than our initial estimates. “
The new distance estimate is that DF2 is 72 million light-years away, compared to 42 million light-years away, as reported by other teams.
This places the galaxy further than the original 2018 Hubble estimate of 65 million light years away.
âThe most precise measurements reinforce the initial conclusion of a dark matter-deficient galaxy,â the astronomers said.
âSo the mystery of why DF2 is missing most of its dark matter still persists. “
The teams paper was published in the Letters from astrophysical journals.
Zili Shen et al. 2021. A tip of the branch of the red giant Distance 22.1 Â± 1.2 Mpc to the dark matter-deficient galaxy NGC 1052-DF2 from 40 imaging orbits of the Hubble Space Telescope. ApJL 914, L12; doi: 10.3847 / 2041-8213 / ac0335