The initial mission of SG-7 and SG-1 to Hanka was to use the newly constructed Douglas McLean Memorial Observatory there to observe a black hole during a total eclipse, however the observatory and the planet were abandoned after an attack by Nirrti.
Earth's first direct encounter with a black hole occurred when SG-10, under the command of Major Henry Boyd, was unable to return from P3W-451, a planet in a binary system which was in orbit around the companion star of a newly formed black hole. The SGC and Earth were connected to the gravitational field of the black hole through the open wormhole, which was able to draw power directly from the black hole itself, making it impossible to disengage. According to the Theory of Relativity, near light-speed velocities or extreme gravity will cause a time dilation. The gravitational field of the black hole extended through the wormhole, expanding outward like a bubble, and making the time dilation worse as the field expanded, eventually slowing to more than 600% below normal. The warping of space/time occurred in advance of the gravitational field rather than as a result of it, probably due to a lensing effect generated by the stargate, and contradicting known facts and accepted theories about time and gravity. Due to the time dilation, two days within the SGC equaled two weeks outside the mountain. The wormhole was eventually disengaged by using a shaped charge directed at the stargate, forcing it to arc to another stargate on P2A-870.
Later, on Vorash, Carter's plan to destroy Apophis's fleet involved redialing P3W-451 and allowing the gravity of the black hole to remove enough stellar matter through the stargate to disrupt the balance between the forces of fusion and gravity in Vorash's sun, thus creating an artificial supernova and destroying the solar system. The coordinates offered to the Aschen also included the black hole on P3W-451.
An Asgard plan to eliminate the Replicators involved the artificial creation of a black hole. After the Replicators had been trapped within the time dilation field on Hala, Thor was entrusted with the task of collapsing Hala's sun by artificially increasing its gravitational field in order to create a black hole that would break apart and consume the planet. The planet was successfully destroyed, however, before reaching the event horizon of the black hole, a large number of Replicator blocks formed a coherent mass and seemed to use the time-dilation device to counteract the gravitational effects that should have drawn them in. The blocks formed a ship, and the Replicators escaped the black hole.
The Ori plan to conquer the Milky Way Galaxy hinged upon the creation of a massive stargate, or supergate, large enough to accommodate the passage of an armada of warships and powerful enough to maintain a connection between galaxies. On the planet Kallana, a force field was established that expanded to engulf the entire planet and collapsed it into a micro-singularity. A wormhole powered by a black hole at either end could span the vast distances between galaxies and remain open indefinitely, however SG-1 successfully prevented the formation of a supergate at Kallana.
The black hole that was created during the destruction of the Ori beachhead at Kallana was later used to establish an inter-universal bridge. An SG-1 team in a parallel universe bisected the singularity by establishing a wormhole from PX7-455 to Earth. They then blasted a bridge into this universe which resulted in a subspace rupture and a ripple effect that drew multiple SG teams from different universes into our reality. The problem was corrected by establishing a return wormhole and using a directed energy weapon to reverse the rupture and invert the convergence effect so that the teams could be returned to their own worlds.
The SGC continued to monitor the galaxy for signs of gravitational disturbances that could indicate another attempt at an Ori beachhead. One such gravitational disturbance near P3X-584 turned out to be another black hole, but there were no signs of supergate activity. At P3Y-229, however, the Ori once again succeeded in collapsing the planet into a micro-singularity and establishing a fully formed supergate through which they launched their invasion of the galaxy. Unable to destroy the supergate, SG-1 attempted to block it by using the power of a black hole in the Pegasus Galaxy. The Odyssey launched a stargate toward the accretion disk of the black hole and established a wormhole to a second stargate released near the supergate. The intense gravity of the black hole distorted Odyssey's sensors and blocked subspace communications. A message from Atlantis to Odyssey had to be relayed first from Atlantis to the SGC via the stargate, then transmitted to SG-11 at the Gamma Site, then forwarded via subspace relay to Teal'c, who could complete the delivery of the message to Odyssey through the open wormhole between galaxies. Odyssey used the black hole's gravity to slingshot the ship away from the accretion disk, and by causing the wormhole to arc from the stargate to the supergate, they successfully established a wormhole to the supergate, powered by a black hole in the Pegasus Galaxy that could maintain the connection indefinitely and effectively prevent the Ori from using the supergate to bring more ships into the galaxy.
Cross Reference: Alternate Reality - Ripple Effect, Aschen, Asgard, Henry Boyd, Frank Cromwell, Paul Davis, Hala, Hanka, Kallana, Odyssey, P3W-451, P3X-584, P3Y-229, Pegasus Galaxy, Replicators, Supergate, Supernova, Time Dilation Device, Vorash, Wormhole Arc
Episode Reference: Singularity, A Matter of Time, Exodus, 2001, New Order, Beachhead, Ripple Effect, The Pegasus Project