The Neutronium Alchemist is the most powerful weapon in Peter F. Hamilton's Night's Dawn universe.
Only one Alchemist was ever made. Physically it takes the form of a sleek, polished silvery conical missile. It is capable of being loaded onto a standard combat wasp, but comes with its own carrier vehicle which is specially designed to 1) withstand a star's heat and radiation far longer than any ordinary projectile and 2) accelerate at up to sixty-five gees, enabling it to outrun even antimatter-powered combat wasp interception.
When triggered, the Alchemist begins to internally manufacture neutronium, effectively forming a black hole. Operating procedure is to launch it into the centre of a planet or star and trigger it remotely. It then either swallows up the entire celestial body or causes it to go nova, depending on how dense a concentration of neutronium is selected. It thus is capable of extinguishing a star - turning it into a black hole. Obviously it can only be used once.
It was designed and built in 2580 by physicist Dr. Alkad Mzu during the escalating war between the star systems Garissa and Omuta over an extremely valuable collection of asteroids called the Dorados. Mzu intended to use it to slay Omuta's star - which would not directly kill any of the planet's inhabitants, but quickly render Omuta uninhabitable, forcing the population to evacuate and winning the war for Garissa. She was present on the ship Beezling which was sent with this secret mission in 2581. However, the ship was ambushed in transit and left drifting, light years from the nearest inhabited system. Mzu was the only one who escaped, leaving the Alchemist and rest of the crew (including her husband, Peter Adul) in zero-tau (stasis) with the intention of rescuing them later.
It was only when she got back to civilization that Mzu discovered that in the intervening time, Omuta had bombed Garissa with antimatter, killing almost everybody on her home planet.
To explain what happened next would be to rehash a major plot arc of The Reality Dysfunction and The Neutronium Alchemist, the first two books in the Night's Dawn Trilogy. However, it can be stated that it was only in 2611 that the Alchemist was eventually recovered and ultimately destroyed - fired into the heart of a nameless gas giant in an uninhabited star system, causing it to go nova. Its only victims were a few ships full of bad guys.