NASA | STScI | HubbleSite | 2018 Mar 28
Galaxies and dark matter go together like peanut butter and jelly. You typically don't find one without the other.Credit: NASA/GSFC/SVS/Katrina Jackson
Therefore, researchers were surprised when they uncovered a galaxy that is missing most, if not all, of its dark matter. An invisible substance, dark matter is the underlying scaffolding upon which galaxies are built. It's the glue that holds the visible matter in galaxies — stars and gas — together. ...
The unique galaxy, called NGC 1052-DF2, contains at most 1/400th the amount of dark matter that astronomers had expected. The galaxy is as large as our Milky Way, but it had escaped attention because it contains only 1/200th the number of stars. Given the object's large size and faint appearance, astronomers classify NGC 1052-DF2 as an ultra-diffuse galaxy. A 2015 survey of the Coma galaxy cluster showed these large, faint objects to be surprisingly common.
But none of the ultra-diffuse galaxies discovered so far have been found to be lacking in dark matter. So even among this unusual class of galaxy, NGC 1052-DF2 is an oddball. ...
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