Tidal disruption events
A tidal disruption event (TDE) occurs when a star wanders within the tidal radius of a supermassive black hole,
R_t ≈ R★ (M_BH / M★)^(1/3),
where the black hole’s tidal forces exceed the star’s self-gravity. For a Sun-like star and a 10⁶–10⁷ M☉ black hole, R_t lies just outside the event horizon — the star is stretched into a long debris stream (“spaghettified”). Roughly half of the debris is unbound and escapes; the bound half falls back at a rate that famously declines as Ṁ ∝ t^(−5/3), feeding a temporary accretion disk. Relativistic apsidal precession causes the returning stream to self-intersect, dissipating orbital energy and circularizing the debris.
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Jetted TDEs
A small fraction of TDEs launch relativistic jets. The prototype, Swift J1644+57 (2011), produced luminous, highly variable X-ray emission for months, with a jet of Γ ~ 10 pointed at Earth — effectively a blazar switched on by a single star. Radio observations of its external shock showed that the conditions required to accelerate protons to 10²⁰ eV appear to be realized in the jet. Only a handful of on-axis jetted TDEs are known (Swift J1644+57, Swift J2058+05, Swift J1112−82, AT2022cmc), implying that most TDE jets point elsewhere.
Why TDEs are attractive UHECR candidates
- Energetics and rates — jetted TDEs plausibly supply the required UHECR luminosity density (~10⁴⁴ erg Mpc⁻³ yr⁻¹).
- Transience — magnetic time delays of 10³–10⁵ yr in cosmic magnetic fields erase the temporal correlation between a burst and its arriving particles, naturally explaining why no source is seen “in the act.”
- Composition — disruptions of evolved stars or carbon–oxygen white dwarfs by intermediate-mass black holes inject intermediate-mass nuclei, matching the gradually heavier composition Auger measures at the highest energies. A nuclear cascade in the jet can simultaneously fit the UHECR spectrum and composition and produce PeV neutrinos.
- Neutrino hints — the TDE AT2019dsg and the candidates AT2019fdr and AT2019aalc have been associated with IceCube alerts, making TDEs one of the few source classes with individual multi-messenger evidence.
Challenges
The volumetric rate of jetted TDEs is uncertain by orders of magnitude, and the observed events are too few for population statistics. Whether the jets persist long enough, and whether nuclei survive the intense radiation fields near the disk, remain active research questions.
Related
- Blazars & AGN jets — persistent jets from accreting black holes
- Gamma-ray bursts — stellar-death transients
- Open questions