The Isa device, also known as the collapsar device, was a technology created by the Asgard Fenrir to use as a weapon against the Replicators by collapsing stars into black holes and thus destroying entire solar systems.
Using a combination of cosmology, temporal physics and matter energy transfer, the isa device is designed to drill down through the layers of normal space into unknown, extradimensional realms of energy. Drawing on levels of cosmic power strong enough to cut through the barriers of quantum reality, the isa device twists gravitation into a lens and blows it outwards, forming a sphere of fast-time a dozen kilometers wide. Once the device is activated, after having been beamed into the heart of a star. Within the isa device's sphere, all matter caught inside ages a trillion times faster than the universe outside of the sphere. Eons pass in milliseconds and within ten seconds, all within the isa device's effect age to nothing. The result of this is that the heart of the star the isa device is used upon is rotted, causing an instant stellar collapse, turning the star into a black hole. (SGA: "Nightfall")
During the Asgard war with the Replicators, the Asgard scientist Fenrir created the isa device as a weapon against them to destroy systems infected with the Replicators before they can react. While conducting an unauthorized test of the isa device, Fenrir experienced a misfire due to radiation interference and six planets were destroyed, including one with a pre-industrial civilization. As punishment for his actions, Fenrir was banished on a five hundred year penal cruise on his ship, the Aegis. (SGA: "Nightfall")
After the Replicators were trapped on Hala by SG-1, the other Asgard would ironically use the isa device to destroy Hala by collapsing its star into a black hole in a failed attempt to destroy the Replicators. (SG1: "New Order, Part 1") (SGA: "Nightfall")
After encountering Fenrir on Heruun in the Pegasus Galaxy, Doctor Rodney McKay and Lt. Colonel John Sheppard learned of the isa device and Fenrir's crimes from the Asgard computer core onboard the Odyssey. The Wraith subsequently learned of the isa device from information downloaded from the computer core by McKay and a single Wraith Queen and her hive ship sought the device as a weapon to destroy the Asurans and gain rule of the Wraith. After the queen sacrificed herself to kill Fenrir, the Wraith onboard the Aegis were able to use the ship's matter converter and the blueprints for the isa device from the Aegis's databanks to synthesize the device. Though Sheppard killed the Wraith before they could deploy it using the Aegis's Asgard transporter, the Wraith Commander was able to activate it. With the Aegis transporter matrix destroyed in the firefight, McKay was unable to beam it to a safe distance nor could he disarm it. Instead, to protect Heruun and end the threat from the hive ship, Colonel Samantha Carter rammed the hive ship with the Aegis and with McKay's help, used the Aegis's Asgard hyperdrive to send the two ships hundreds of light years away into the interstellar void between star systems where the device could cause no harm to a solar system. There, the isa device detonated, aging both the Aegis and hive ship to dust. (SGA: "Nightfall")