Yale Astronomers Find 3rd Dark-Matter-Free Galaxy at 100 Million Solar Masses
Updated
Updated · Universe Today · Jul 1
Yale Astronomers Find 3rd Dark-Matter-Free Galaxy at 100 Million Solar Masses
3 articles · Updated · Universe Today · Jul 1
Summary
DF9, a faint dwarf galaxy 45 million light-years from Earth, became the third known galaxy found to lack dark matter after Yale-led astronomers measured only about 100 million solar masses—fully explained by visible matter.
Keck Observatory data tracked stellar motions inside DF9, and the team said any normal dark-matter halo would have lifted the galaxy’s mass by roughly a factor of 100.
DF9 sits with DF2 and DF4 in a seven-galaxy linear structure, strengthening the idea that all three formed in a single violent event rather than through standard halo-based galaxy formation.
The researchers propose a high-speed galaxy collision stripped star-forming clouds from their dark-matter halos, creating galaxies from ordinary matter alone and offering fresh evidence that dark matter behaves like a physical substance.
Follow-up observations, including searches for leftover gas from the suspected collision, aim to test that formation scenario and could force revisions to leading models of how galaxies form.
Three galaxies in a row lack dark matter. Is this a fluke, or a clue that rewrites our theory of the universe?
A galaxy was stripped of its invisible dark matter. But where did 99% of its original mass actually go?
Was this 'ghost galaxy' born from a cosmic collision, or ripped from the arm of a larger galaxy?
Three Galaxies Without Dark Matter: The Discovery of DF9 and Its Implications for Cosmology
Overview
A major breakthrough in astrophysics has revealed NGC 1052-DF9 (DF9) as the third known galaxy that appears to lack dark matter, joining DF2 and DF4. This discovery challenges the standard view of galaxy formation, as these galaxies align in a peculiar linear structure, hinting at a shared origin. Astronomers determine dark matter content by comparing the motion of stars to what is expected from visible matter alone. In DF9, the observed stellar motions match what is predicted from its stars, showing no need for dark matter and strengthening the case for a new class of galaxies that defy conventional models.