The Cartwheel Galaxy is approximately 500 million lightyears away. It is a ring galaxy which was likely once a spiral galaxy like the Milky Way but suffered a collision with a smaller galaxy around 150,000 years ago. It is estimated to be 150,000 light years across with a mass of about 2.9 to 4.8 x 109 solar masses, and rotates at 217 km/s.
It is theorized that this galaxy may have a larger instance of exotic subspace events and anomalies created when the two galaxies interacted with each other, though this is only theorized.
Subspace Accelerator Accident
In 2379 Section 31 was conducting experiments with a Subspace Accelerator in the Homam Star System which probably sent several vessels at extreme velocity into this galaxy. Given the extreme range of the galaxy from the Milky Way, it is considered nearly impossible to determine exactly where such a vessel might have been sent or if the ship and its crew survived.