Black hole

A black hole is a concentrated singularity of gravity which aborbs everything within it's reach, including light. Black holes cannot be seen, but the accretion disk, which is the flow of matter being pulled by the black hole, is visible.

While dialing P3W-451, the SGC was caught by a black hole consuming the planet. Unable to end the connection, Earth would so be swallowed by the black hole. As they got closer, time slowed down, causing the SGC to lose contact with the rest of the outside world. The connection was broken when an explosive was placed just away from the Stargate, causing the wormhole to jump to another gate.

Supergates are powered by black holes, and this could mean that their wormholes could last indefinitely.