Hubble Views ‘Ghostly’ Galaxy Lacking Dark Matter
This large, fuzzy-looking galaxy is so diffuse that astronomers call it a “see-through” galaxy because they can clearly see distant galaxies behind it.
The ghostly object, catalogued as NGC 1052-DF2, doesn’t have a noticeable central region, or even spiral arms and a disk, typical features of a spiral galaxy. But it doesn’t look like an elliptical galaxy, either. Even its globular clusters are oddballs: they are twice as large as typical stellar groupings seen in other galaxies.
All of these oddities pale in comparison to the weirdest aspect of this galaxy: NGC 1052-DF2 is missing most, if not all, of its dark matter. An invisible substance that makes up the bulk of our universe, 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 galaxy contains at most 1/400th the amount of dark matter that astronomers had expected. But how it formed is a complete mystery.
The galactic oddball is as large as our Milky Way, but it had escaped attention because it contains only 1/200th the number of stars as our galaxy. Given the object’s large size and faint appearance, astronomers classify NGC 1052-DF2 as an ultra-diffuse galaxy.
Based on the colors of its globular clusters, NGC 1052-DF2 is about 10 billion years old. It resides about 65 million light-years away.
The image was taken Nov. 16, 2017, by Hubble’s Advanced Camera for Surveys.