P3W-451 was a planet in the Milky Way galaxy that held a Stargate and was dangerously near the event horizon of a black hole. It was explored on a tragic mission by SG-10. The planet was formerly orbiting a Binary star and had a moon.
The planet was formerly in Goa'uld control and they had transplanted people from ancient Egypt. (RPG: "Friends and Foes: Stargate Season Two") The planet was also dangerously close to the event horizon of a black hole. SG-10 was sent on a routine reconnaissance mission to the planet, only to discover that all life on the planet had recently died out for an unknown reason. During the time they were there, one of the stars the planet orbited turned into a black hole.
While attempting to establish contact with SG-10, Earth was inadvertently linked to the black hole. The extreme gravity and time dilation came through the Stargate and effected Earth while the SGC was unable to shut the Stargate down. The black hole's effects became a grave threat to Earth before Captain Samantha Carter came up with the plan to use a shaped charge to jump the wormhole to another Stargate, effectively severing the connection between Earth and P3W-451. The plan worked and the wormhole jumped to P2A-870, allowing the SGC to finally shut down the Stargate and saving the world. SG-10 remained trapped on the planet, beyond any apparent hope of rescue. (SG1: "A Matter of Time")
When planning to destroy Apophis' fleet, SG-1 used a Stargate to dial P3W-451 and launched it into the star that Vorash orbited. The black hole absorbed the mass, and caused the star to supernova, destroying Apophis' fleet. Due to time dilation, the stellar matter didn't actually arrive until nearly three years later. (SG1: "Exodus", "The Cost of Honor")
When Stargate Command went into negotiations with the Aschen, the SGC offered them a list of addresses as a sign of good faith. When suspicions arose as to the true nature of the Aschen's relations with the Volians, the list of addresses was altered. The first address was that of the black hole of P3W-451. The other addresses supposedly lead to worse planets. The Aschen later dialed the address, but while they apparently managed to find a way to close the wormhole, Mollem and several of their leaders were killed. (SG1: "2001", "Relativity")
Five years later, upon learning of an anti-gravity technology that could allow them to safely return to the planet via ship, SG-1 launched a dangerous rescue mission to the planet for SG-10. Using stolen designs from the Kinahhi and a power source from Ba'al, SG-1 was able to create an anti-gravity shield around a Tel'tak and fly it to P3W-451 which was now within the event horizon of the black hole. To SG-10, it had only been a very short time since the black hole was created and they had multiple failed dial outs to Earth. Due to the time dilation, the mass of Vorash's sun had not yet arrived either. Due to the plans to the device being sabotaged, the shield failed and the Tel'tak crashed on the planet, but using wiring from the MALP, Major Samantha Carter was able to fix it. Before the two SG teams could leave though, the wormhole from Vorash finally opened and Lieutenant Reed was incinerated. SG-1 and the rest of SG-10 managed to escape on the Tel'tak however and Carter got the shield working once again, allowing them to escape to hyperspace. However, everything else on the planet was incinerated by the heat from Vorash's sun. Due to the time dilation, while to SG-1 it seemed like less than an hour, they were gone for five months to the rest of the universe. (SG1: "The Cost of Honor")