Penrose Xray Cannon:
A mirror shell is constructed around a super massive blackhole with a powerful xray laser. The xray beam is then shot inside the sphere and with the help of the penrose process and superradiant scattering a massive beam of energy is shot out the other end shaped using extremely strong magnetic fields generated by magnetars.
The resultant energy beam has the capability to cause a supernova in nearby stars and sterilize entire solar systems.