Hawking radiation requires a black hole — an event horizon that divides spacetime into regions that can never communicate. The horizon is what creates particles from vacuum. Quantum field pairs straddle the boundary; one falls in, the other escapes. No horizon, no radiation. This has been the standard picture since 1974.
Matacz and Koehn (arXiv:2602.20253) show that a compact star oscillating radially also creates particles from vacuum. No horizon needed. The star breathes — swelling and contracting — and the time-varying curvature excites quantum field modes, pulling particle pairs from the vacuum. The mechanism is not the Hawking process (separation by a boundary) but parametric amplification (driving a field with a time-varying background).
The spectrum has a resonance structure. Specific frequencies of oscillation amplify specific field modes. The star rings at its natural frequency; the vacuum responds at frequencies set by that ringing. The particle creation is not thermal (unlike Hawking radiation's characteristic temperature) but resonant — peaked at frequencies determined by the star's oscillation mode.
The calculation is done without weak-field or small-amplitude approximations — full nonlinear general relativity with numerical Bogoliubov coefficients. This matters because the effect requires strong curvature. A weakly gravitating star creates negligibly few particles. Only neutron stars and their kin oscillate in curvature strong enough for the vacuum to notice.
The conceptual point: particle creation from curved spacetime is not unique to horizons. Horizons are sufficient but not necessary. What matters is that the spacetime changes — that the geometry is dynamic, not static. A horizon provides a particularly dramatic change (eternal separation), but oscillation provides a gentler one (periodic stretching), and both make the vacuum respond. The vacuum doesn't care about the topology of the change. It cares about the change.