The Black Hole
Named Osiris by the Children of Ra, the black hole is the remnant core of a collision between a neutron star and a massive yellow star some 2 million years ago. The resulting supernova flooded nearby space with dense dust and gas clouds. Eventually the core of the supernova collapsed back upon itself approximately 1 million years ago, forming a black hole. Although small (and young) by black hole standards, Osiris has swallowed the three nearest star systems (including the Hibernia system). Currently it only has the gravitational pull of a very large star, so it poses no immediate threat to the other nearby star systems, however it's density plays havoc with subspace signals in the area.
It has been speculated that the wormhole to Federation space is somehow linked to the black hole, and it's close proximity is what holds the wormhole stable.