A ZPM
In physics, zero-point energy is the lowest possible energy that a quantum mechanical physical system may possess and is the energy of the ground state of the system.
Zero Point Modules are incredibly long-lived power sources of great magnitude, which draw zero point energy from artificially created layers of subspace. Another way to draw zero point energy is by using a matter bridge. (SG1: "Lost City, Part 1", SGA: "Rising")
The power core of an Ori warship uses zero point energy as an energy source.
In real life, the Zero Point Energy of vacuum space is theorized to roughly have the same density as the core of the sun.