Grand, majestic spiral galaxies like our Milky Way are hard to miss. Astronomers can spot these vast complexes because of their large, glowing centers and their signature winding arms of gas and dust, where thousands of glowing stars reside.

But some galaxies aren't so distinctive. They are big, but they have so few stars for their size that they appear very faint and diffuse. In fact, they are so diffuse that they look like giant cotton balls.

Observations by NASA's Hubble Space Telescope of one such galaxy have turned up an oddity that sets it apart from most other galaxies, even the diffuse-looking ones. It contains little, if any, dark matter, the underlying scaffolding upon which galaxies are built. Dark matter is an invisible substance that makes up the bulk of our universe and the invisible glue that holds visible matter in galaxies — stars and gas — together.

Called NGC 1052-DF2, this "ghostly" galaxy contains at most 1/400th the amount of dark matter that astronomers had expected. How it formed is a complete mystery. The galactic oddball is as large as our Milky Way, but the galaxy had escaped attention because it contains only 1/200th the number of stars as our 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.

Lee esta historia en español.