Now, Darkish Matter Free! | by Brian Koberlein

Hubble House Telescope

The above picture may not look uncommon, nevertheless it poses an attention-grabbing thriller for astronomers. Captured by the Hubble House Telescope, it’s a picture of an ultra-diffuse galaxy (UDG) generally known as FCC 224. In contrast to common dwarf galaxies such because the Magellanic Clouds, these galaxies have an unusually low floor brightness for a galaxy of their dimension. This normally means they include numerous darkish matter. The gravity of the darkish matter holds the galaxy collectively slightly than the celebs and cosmic mud.

The usual cosmological mannequin predicts UDGs. Since darkish matter is extra frequent than common matter, it’s the clumping of darkish matter that drives galaxy formation. Generally a darkish matter clump can kind with out a variety of stellar materials round, and also you get a galaxy with out numerous stars. However lately, astronomers have discovered that some diffuse galaxies aren’t dominated by darkish matter. The proof pointing to a scarcity of darkish matter wasn’t definitive, nevertheless it was robust sufficient for astronomers to marvel about how such a galaxy might kind. One concept is that they’re a results of a latest collision that stripped the diffuse galaxy of its darkish matter. Different astronomers argue that such a galaxy would help various fashions, akin to modified gravity.

This new galaxy has two issues going for it. The primary is that FCC 224 just isn’t a part of a galactic cluster generally known as the NGC 1052 group. This implies we will simply argue that these odd UDGs are the results of some distinctive property of a selected cluster. In a single examine, ^{the authors present that there are shared traits amongst these galaxies, akin to having previous, metal-poor stars, low ranges of mud, and a sluggish price of rotation. This means that darkish matter free ultra-diffuse galaxies will be categorized as a particular kind of galaxy.}

A second examine seems at globular clusters with FCC 224. ^{They’re unusually small and tightly packed, which might throw a wrench within the collision mannequin. If a collision was robust sufficient to strip the galaxy of darkish matter, it also needs to have been robust sufficient to disrupt the globular clusters.}

General, these research affirm the existence of ultra-diffuse galaxies with out darkish matter, and their existence suggests we could must revise the usual mannequin.