The starbreaker is the primary weapon used by the Xeelee. It has only been observed in use on the nightfighter starships. The starbreaker is a gravity wave beam weapon that has the ability to destroy a star. The starbreaker was first observed in the short story Blue Shift (Vacuum Diagrams). In this story, the Qax (another alien race that has conquered Man) have found a damaged nightfighter. The only thing aboard is a small object that is similar to a handgun with delicate wire wrapped around the barrel, and controls described as being for hands smaller than a human's.
At low power settings, the device emits synchrotron radiation, but the Qax have been too scared to try the higher settings. It is not until later in the story when Jim Bolder, piloting the nightfighter for the Qax, discovers the true nature of the device when he witnesses a small fleet of nightfighters destroying a star with cherry-red beams. After hatching a plot to change his entry point into the Qax system, this theory is proven when the starbreaker is accidentally fired into the system's sun at full power in an attempt to destroy the nightfighter. The star begins destroying itself within four days.
The beams emitter by a starbeaker are consistently described as thin beams of cherry red that emit from Nightfighters and other Xeelee vessels encountered around Bolder's Ring. In the short story Blue Shift the source of the Starbreaker is described as a pistol-like device designed for hands the size of a human child. There is intricate wiring around the handle and an adjustment knob on the back. It will emit synchrotron radiation on the lowest setting, suggesting that it is powered by some form of particle acceleration.
The full capabilities of the starbreaker have never been clearly explained. For example, it is not known if the weapon makes use of direct energy transfer, or if the stellar disruption effect is due to some other mechanism. Furthermore, with the variable outputs of the device, it remains uncertain as to what magnitude of damage it can inflict upon "normal" targets. It would seem reasonable to assume that the device is formidable no matter what the mechanism, as the Xeelee have found it to be quite effective for their needs.
Presumably since it is capable of destroying stars the Starbreaker (like most Xeelee equipment) was designed with the Photino birds in mind.