The light curves of radioactive transients, such as supernovae and kilonovae,
are powered by the decay of radioisotopes, which release high-energy leptons
through $\beta^+$ and $\beta^-$ decays. These leptons deposit energy into the
expanding ejecta. As the ejecta density decreases during expansion, the plasma
becomes collisionless, with particle motion governed by electromagnetic forces.
In such environments, strong or turbulent magnetic fields are thought to
confine particles, though the origin of these fields and the confinement
mechanism have remained unclear. Using fully kinetic particle-in-cell (PIC)
simulations, we demonstrate that plasma instabilities can naturally confine
high-energy leptons. These leptons generate magnetic fields through plasma
streaming instabilities, even in the absence of pre-existing fields. The
self-generated magnetic fields slow lepton diffusion, enabling confinement and
transferring energy to thermal electrons and ions. Our results naturally
explain the positron trapping inferred from late-time observations of
thermonuclear and core-collapse supernovae. Furthermore, they suggest potential
implications for electron dynamics in the ejecta of kilonovae. We also estimate
synchrotron radio luminosities from positrons for Type Ia supernovae and find
that such emission could only be detectable with next-generation radio
observatories from a Galactic or local-group supernova in an environment
without any circumstellar material.

Dieser Artikel untersucht Zeitreisen und deren Auswirkungen.

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