Item from deaths-end by
A near-lightspeed mass-dot — the dark-forest weapon that ends a star and the system around it. The Trisolarans receive one before humanity does.
The photoid (光粒) is the standard medium-power dark-forest strike: cheap, clean, and reliably system-killing. A pellet of ordinary matter at near-c carries kinetic energy comparable to a planet's gravitational binding energy; striking a star, it gouges out a stream of plasma sufficient to sterilize the orbiting worlds in light-hours. Trisolaris is destroyed by a photoid early in Death's End; another is prepared for the Solar System but Singer chooses the dual-vector foil instead.
A single grain of matter, no larger than a marble, accelerated to near-lightspeed. Invisible from any direction except its line of approach, against which it appears as a single relativistically blue-shifted point. On impact with a star, the result is a brief intense disturbance in the photosphere that ejects a vast plume of stellar material.