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Starts With A Bang

Starts With A Bang podcast #64 — Galaxies Without Dark Matter

(Image credit: Montes et al., 2020, ApJ.)

We’ve found our first ones! The question is: how did they survive?


Over the past 2 years, an exciting development has finally arisen: scientists have measured a large number of small, diffuse galaxies exquisitely well, and have finally found their first candidate galaxies that appear to have no dark matter at all. Whereas large cosmic structures typically have dark matter-to-normal matter ratios of 5-to-1, smaller structures typically have higher ratios, as star formation will kick some of the normal matter out but leave the dark matter intact. However, there should be a second type of galaxy: stars without dark matter, as tidal interactions can rip the normal matter out and keep it out. But these structures are easy to destroy, and so shouldn’t persist for very long.

How, then, did we find a galaxy that both appears to have no dark matter and also appears to have not formed any new stars in ~7 billion years or more? While the science is still ongoing, I’m so pleased to welcome Dr. Mireia Montes onto the program, whose recent paper may have just solved the mystery.

Have a listen and enjoy the show; there’s a lot of astronomy in here for you to enjoy!


Starts With A Bang is written by Ethan Siegel, Ph.D., author of Beyond The Galaxy, and Treknology: The Science of Star Trek from Tricorders to Warp Drive.


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