Remember the announcement of a galaxy with no dark matter? It’s just been re-examined, with astounding results.
In theory, all galaxies should contain copious amounts of dark matter, with one exception.
Galactic mergers, interactions, or gas stripping events can isolate large amounts of normal matter.
These liberated clumps should gravitate and recollapse, creating dark matter-free galaxies.
Detractors argued their absence proved dark matter’s non-existence.
However, 2018 and 2019 saw scientists announce two dark matter-free galaxies: NGC 1052-DF2 and NGC 1052-DF4.
The key advance was measuring their velocity dispersions, an achievement enabled by modern instrumentation.
Those measurements, combined with parent galaxy NGC 1052’s distance, allowed reconstruction of their total masses.
With distances estimated at ~60–70 million light-years, their galactic properties indicate a dark matter-free composition.
Previously, a direct measurement of NGC 1052-DF2’s surface brightness fluctuations yielded that same distance, but doubts persisted.
A different team claimed these galaxies belong to a closer foreground group, implying a typical dark matter density.
Hubble measurements of the other galaxy, NGC 1052-DF4, were taken to settle the controversy.
Using stars from the tip of the red giant branch, a distance of 61 million light-years was determined, consistent with no dark matter.
If these galaxies truly possess the sizes, distances, and velocity dispersions measured, they must be dark matter-free.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.