Black holes, when size doesn't matter

Tidal disruption events involve a star being destroyed by a black hole, with the resulting stellar matter forming an accretion disk around the black hole. This debris can either fall into the event horizon or be expelled as winds or jets. The behavior of this ejected matter depends on how quickly the black hole feeds. Research by Goodwin and Mummery studied twenty tidal disruption events to analyze these flows. They found two phases of matter expulsion related to accretion rate: an initial phase when accretion rates exceed the Eddington limit, leading to powerful outflows, and a later phase occurring when the accretion rate drops to about two percent of the Eddington rate. This latter, later flow is associated with the formation of compact radio jets. The existence of these flows is not guaranteed in all events, as simulations indicate that some systems take many years to reach the critical accretion rates necessary for the later phase.

The underlying framework suggests a universal critical threshold, defined by the Eddington limit relationship, governs when black holes transition between different states of matter expulsion. The observation that this same rule applies across stellar-mass black holes and supermassive black holes—despite immense mass differences—suggests an intrinsic physical mechanism dictated by accretion physics rather than the black hole's absolute size. This universality points toward a fundamental bifurcation in accretion state driven by critical density thresholds, implying that the onset of powerful jet production is governed by the efficiency of energy conversion relative to gravitational limits, regardless of the scale of the object. The uncertainty surrounding why not all events show these flows—explained by simulation modeling concerning timescale versus critical rate crossing—introduces a layer of complexity regarding observational selection effects or true physical rarity. This pattern invites questioning whether the observed variations are truly random sampling or indicative of complex, multi-scale evolutionary pathways that require more comprehensive temporal observation to fully map.