VIRGOHI21

A dark galaxy within the Virgo Cluster, VIRGOHI21 is composed entirely of dark matter. The mysterious object is located about 50 million light years from the Milky Way.

The dark galaxy appears to have collided with NGC 4254 within the last 100 million years, causing the unusual shape of the visible galaxy. Gas is being siphoned away into a tenuous stream, and one of its spiral arms is being torn off by the invisible dark matter object.

It's possible that VIRGOHI21 has always been this way, formed from primordial dark matter and neutral hydrogen after the Big Bang. It's been cruising the Universe ever since, disrupting galaxies as it goes.

Alternatively, the object might be the wreckage from a collision of galaxy clusters; a shred of dark matter hurled out into space.