A "Starbuster" is a character or weapon which has the capability to destroy a star, or produce an attack equal to an exploding star.
"Starbuster" (I like Star Destroyer better, but Star Wars took it!) is the next step up from a planetbuster, and in reality, would follow the same principal of gravitational binding energy to perform. Being a "Starbuster" in the OBD, like a planetbuster, would at the minimum conform to destruction of a star by overcoming its gravitational binding energy.
For our own Sun, the energy needed is actually 6.87xE41 joules or around 164.913 tenatons, and that is over 3 billion times the energy required for earth. This is a LOT.
However, the Sun is actually larger and brighter than most stars in the visible universe, and the sizes of stars vary greatly (much like planets). For this reason, there are two other sub-categories in the general "star busting" range.
Small: This is the energy required to destroy the smallest stars, which are red dwarves many times smaller than the Sun. This would require around 2.998 tenatons.
Large: This sub-category corresponds to the most massive stars - blue giants. A typical blue giant star like Rigel (used as the benchmark here) has a gravitational binding energy of around 330.544 tenatons.
In fiction, "Starbusters" come in two types: those which equal power to an exploding star/can destroy a star, or those which achieve it by chain reaction/non brute force. In the OBD, a "Starbuster" of the direct variety would be considered much much more powerful, since they can bring the energy of a star's destruction to bear as an attack anywhere, whereas a device which causes a star to become unstable requires that the device is deployed to the star in order to work, and it's actual destructive power is nowhere near enough as it is.
Characters/Weapons that can destroy stars/create attacks equal to supernova:
- Archangel (Image Comics)
- Archangels from ToAru
- Some Bastard!! characters
- Broly (Dragon Ball Movies)
- C'Tan, GEoM, Warmaster Horus and some technologies from Warhammer 40,000
- The Eclipse Cannon and Final Egg blaster from Sonic the Hedgehog
- Emperor Charon and other characters from Crossgen Comics
- Forerunners (Halo)
- Green Lanterns and many others from DC Comics
- The Hand of Omega, most TARDIS, and various other technologies from Doctor Who
- Ideon (Space Runaway Ideon)
- Pyron from Darkstalkers
- Morgoth (The Silmarillion)
- Many Saint Seiya characters
- Many Sailor Moon characters
- Several Sith Lords in Star Wars when their power is focused through special crystals (chain reaction)
- Silver Surfer and all Heralds of Galactus, Gladiator, Drax the Destroyer, and many others from Marvel Comics
- Sirius from Megaman Starforce
- Sun Crusher through chain reaction and the Centerpoint Station (Star Wars EU)
- Trilithium Torpedos through chain reaction (Star Trek)
- Unicron (Transformers)
- Valdurmon, Tactimon, and a few others (Digimon)
The next step up from a "Starbuster" would be destroying entire star systems/clusters, and then even galaxies.
- Destructive Capacity
- Gravitational Binding Energy
- Life Wipers
- TNT Equivalent