= Collisionless black-hole capture
Collisionless matter approaching a <black hole> generally cannot dissipate enough orbital energy to remain bound, so direct capture requires sufficiently small <angular momentum>. For nonrelativistic incident speed $v$, a <Schwarzschild black hole> has direct test-particle capture cross-section approximately $16\pi G^2M^2/(c^2v^2)$. A Newtonian pericentre estimate using the <Schwarzschild radius> instead gives $4\pi G^2M^2/(c^2v^2)$. Both show that capture at a given mass density is suppressed by order $(v/c)^2$ relative to supersonic <Bondi--Hoyle--Lyttleton accretion>. <Tidal disruption events> provide a distinct way to accrete some stellar debris.
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