A comet near our Sun is a familiar object. Ice sublimes, gas drags dust off the surface, radiation pressure sculpts a tail. Water molecules released at 1 AU survive for hours before photodissociation. Sodium and iron atoms persist as neutrals. The physics is gentle enough that we can watch the process unfold over weeks.
Place the same comet near β Pictoris — an A-type star 8.7 times more luminous than the Sun — and gentle becomes violent. Water molecules survive 1.5 seconds at 0.2 AU. Neutral iron photo-ionizes in under a minute. A half-micron olivine grain sublimes in a single day at 0.18 AU (it would need to be three times closer to the Sun for the same fate). Everything we associate with cometary behavior — gas coma, dust tail, gradual mass loss over an orbit — collapses into something faster and more extreme. No water has ever been directly detected around β Pictoris exocomets. Only CO, which is harder to destroy.
Vrignaud et al. survey exocometary physics across four stellar environments, and the variation is not a matter of degree. Each star creates a qualitatively different regime for mass loss. Around the M-dwarf AU Microscopii, intense stellar winds dominate. Around β Pictoris, radiation obliterates molecules before they travel a single kilometer. Around the white dwarf WD 1145+017, tidal forces disintegrate the body itself — cometary physics has become planetary destruction. The dust activity in that system has, as of 2025, completely ceased. Whatever was falling apart has finished falling apart.
The β Pictoris over-representation in exocomet detection is explained by this same violence. The intense radiation that destroys volatiles instantly also makes the surviving species — ionized metals, CO, refractory dust — detectable across wider orbital distances. A-type stars don't host more comets. They make comets more visible by destroying them faster.
This is the kind of result that reframes a selection effect as physics. The observational bias (we see more exocomets around hot stars) and the physical explanation (hot stars destroy comets more efficiently, producing brighter signatures over larger volumes) are not separate facts to be distinguished. They are the same fact stated at different levels of description.
The deepest contrast is between the Solar System and WD 1145+017. Our comets die slowly — a few meters of surface loss per orbit, enough to survive thousands of passages. The white dwarf's bodies die completely. The sublimation zone is 0.03 AU, smaller than the Sun's own radius. Inside that boundary, nothing survives. The system is not observing cometary physics. It is observing the final stage of planetary system destruction, using the same observational signatures that elsewhere indicate ongoing activity. The same tail means different things around different stars.