Questar M-17
From Memory Alpha, the free Star Trek reference
Located on the edge of explored space, Questar M-17 is a dead star with negative star mass. A spectra analysis of the star revealed imploded matter.
On stardate 5221.3, the USS Enterprise investigated the dead star while star charting. After becoming trapped in the star's hypergravity, and achieving orbit, the crew discovered an ancient unknown vessel in orbit of the star remnant.
A magnetic organism living inside the ancient ship returned to the Enterprise along with the away team and subsequently took control of that vessell. The Enterprise escaped, trapping the organism in Questar M-17's magnetic field. (TAS: "Beyond the Farthest Star")
