GALAXY WITH­OUT DARK MAT­TER

All About Space - - The Impossible Star -

Astronomers have be­come con­fi­dent that most of the mat­ter in the uni­verse is made of a shad­owy sub­stance called dark mat­ter. It is the glue that binds gal­ax­ies to­gether. An­other way to think of it is as the scaf­fold on which the uni­verse’s con­struc­tion projects are built. So it was shock­ing to find a galaxy seem­ingly de­void of it ear­lier this year. Known as NGC 1052-DF2, its lack of dark mat­ter was dis­cov­ered us­ing the Dragon­fly Tele­photo Ar­ray in New Mex­ico.

The team be­hind the dis­cov­ery stud­ied ten star clus­ters or­bit­ing close to the galaxy. They were trav­el­ling far slower than ex­pected, sug­gest­ing there’s scant grav­i­ta­tional pull from lo­cal dark mat­ter to ac­cel­er­ate them to high speeds. The job now is to fig­ure out how the 10-bil­lion-year-old galaxy formed with­out it. Some are call­ing it the im­pos­si­ble galaxy. It could turn out to be a blow for an al­ter­na­tive the­ory to dark mat­ter: mod­i­fied grav­ity. Ad­vo­cates for the the­ory say grav­ity works dif­fer­ently at dif­fer­ent scales. Yet that would af­fect all gal­ax­ies equally. The fact this one is miss­ing dark mat­ter sug­gests the shad­owy sub­stance is re­ally out there, just not here.

ob­ser­va­tions of NGC 1052-DF2show lack of dark mat­ter

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