NGC 1052-DF2 was said to ‘defy theory,’ incorrectly, by many. Here’s what our current theories actually predict.
Last week, astronomers announced the discovery of NGC 1052-DF2: a galaxy without dark matter.
While most galaxies have much more dark matter than normal matter, this one, found nearby a giant elliptical, has practically none.
It’s the first of its kind, but doesn’t defy theories. Here are 5 ways to make “DF2.”
1.) From stripped gas in a cluster. When galaxies speed through the intra-cluster medium, their gas can get stripped out, creating new stars in isolation, without dark matter.
2.) Ejected from galactic mergers. When two galaxies smash together, they usually merge entirely, but sometimes there is ejected material. Sufficient amounts could create a baryons-only galaxy.
3.) Quasar outflows. The outflows from supermassive-black-hole-powered galaxies can recollapse to form their own galaxies. Normally, they create dwarf galaxies, but DF2 is potentially larger.
4.) Evolved Voorwerpjes. Galaxies sometimes have green, glowing companions: stripped and ionized material.
DF2 could be an evolved, 10,000,000,000 year old analogue of Hanny’s Voorwerp.
5.) There is no dark matter. And, somehow, some galaxies might feel normal gravity from the normal matter, rather than obeying MOND.
If all galaxies follow the same underlying rules, only their compositions can differ.
A dark-matter-free galaxy implies a dark-matter-rich Universe.
Mostly Mute Monday tells the astronomical story of an object, image, or phenomenon in pictures, visuals, and no more than 200 words.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.