NASA | GSFC | STScI | HubbleSite | 2021 Jun 17
When astronomers using NASA's Hubble Space Telescope uncovered an oddball galaxy that looked like it didn't have much dark matter, some thought the finding was hard to believe and looked for a simpler explanation.NGC 1052-DF2: This Hubble Space Telescope snapshot reveals 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. Called
an ultra-diffuse galaxy, this galactic oddball is almost as wide as the Milky Way,
but it contains only 1/200th the number of stars as our galaxy. The ghostly galaxy
doesn't appear to have a noticeable central region, spiral arms, or a disk.
Image Data: NASA, ESA, STScI, Zili Shen (Yale), Pieter van Dokkum (Yale),
Shany Danieli (IAS). Image Processing: Alyssa Pagan (STScI)
Dark matter, after all, is the invisible glue that makes up the bulk of the universe's matter. All galaxies appear to be dominated by it; in fact, galaxies are thought to form inside immense halos of dark matter.
So, finding a galaxy lacking the invisible stuff is an extraordinary claim that challenges conventional wisdom. It would have the potential to upset theories of galaxy formation and evolution.
To bolster their original finding, first reported in 2018, a team of scientists ... followed up their initial study with a more robust Hubble look at the galaxy, named NGC 1052-DF2. Scientists refer to it simply as "DF2."
"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."
Determining the amount of the galaxy's dark matter hinges on accurate measurements of how far away it is from Earth.
If DF2 is as far from Earth as van Dokkum's team asserts, the galaxy's dark-matter content may only be a few percent. The team's conclusion is based on the motions of the stars within the galaxy; their velocities are influenced by the pull of gravity. The researchers found that the observed number of stars accounts for the galaxy's total mass, and there's not much room left for dark matter.
However, if DF2 were closer to Earth, as some astronomers claim, it would be intrinsically fainter and less massive. The galaxy, therefore, would need dark matter to account for the observed effects of the total mass. ...
Going the Distance to Confirm a Galaxy with Almost No Dark Matter
Yale University | 2021 Jun 17
Hubble Data Confirms Galaxies Lacking Dark Matter
Institute for Advanced Study (IAS) | 2021 Jun 17
A Tip of the Red Giant Branch Distance of 22.1 ± 1.2 Mpc to the Dark Matter Deficient
Galaxy NGC 1052–DF2 from 40 Orbits of Hubble Space Telescope Imaging ~ Zili Shen et al
- Astrophysical Journal Letters 914(1):L12 (2021 Jun 10) DOI: 10.3847/2041-8213/ac0335
- arXiv.org > astro-ph > arXiv:2104.03319 > 07 Apr 2021 (v1), 20 May 2021 (v2)