Stellar Engine

Basic Information

A Stellar Engine is a category of megastructure that converts a star's radiation into usable energy. There are three categories of Stellar Engine:

• Class A: A propulsion system for moving a star, and everything orbiting the star. See Shkadov thruster and Caplan Thruster.
• Class B: A system for utilizing the all (or the vast majority) of the energy of a star. See Dyson Sphere and Matrioshka Brain.
• Class C: Combines both of the above classes. Utilizes all the energy of a star to, among other things, relocate that star. A Dyson Bubble could be built to be a Class C.

The creation of a Stellar Engine (especially types B & C) would push your civilization to Phase II on the Kardashev Scale.

Sources

Bibliography

1. Wikipedia

2. Kurzgesagt video on Stellar Engines

Game and Story Use

• Scientists discover a rogue star, on course to impact with our solar system in about a decade. As that time approaches and we get better imaging of the system, we realize that it's actually a Stellar Engine, and this may be first contact with an alien intelligence. They do not answer our radio transmissions - is the driver asleep at the wheel?
  • Recent SETI research suggests that radio transmissions may become lost in the cosmic background radiation after traveling just a couple of light years. The further they go, the weaker they get, due to the Inverse-Square Law. So it makes sense we won't hear from them till they get close enough to do some harm.
  • Or perhaps an entire solar system is nothing more than a ghost ship.
  • Possibly an unexpected side effect of firing up the stellar engine (or some result of the movement of the system) has killed everyone. Or perhaps the system has been in motion a very long time…
• We send an entire star at the enemy! This would be a terrible weapon, in every sense of the word. On the one hand, even if the target destroys the stellar engine before collision, the effects of another sun positioned at the edge of your system have got to play astronomical havoc. On the other hand, wouldn't interstellar nuclear missiles be easier? Still, it may be just crazy enough for a pulp-influenced game.
  • Using one star to destroy another is probably less silly than converting an entire planet into a gun that somehow fires its primary at other planets at FTL speeds.
• If advanced civilizations build megastructures that suck up all the energy from their systems, then the universe might not be as empty as we imagine. The truth behind dark matter might just be that 20% of the universe is made up of Type II+ Kardashev cultures with extremely efficient energy converters. No light escapes their stars for us to see. Of course, you'd still have to explain why there's no signs of such things under construction, how they communicate and travel without leaving signs, etc, but there's some potential to make this work for your settings' back story.
  • Speaking of which possible signs have cropped up in a couple of places…
• For more ideas, see Stellar Megastructure.