ASTRO In the literature: contested

What mechanism produces coherent pulsar radio emission?

In plain words

Pulsar radio waves are so bright that huge numbers of electrons must radiate in step (coherently), and the process that synchronizes them is not established.

Precise statement

Pulsar radio brightness temperatures exceed $1e25\,\mathrm{K}$. Identify the mechanism (plasma instabilities in the outflow, coherent curvature radiation from charge bunches, direct emission from nonstationary pair discharges) that reproduces the mean spectrum (flux ~ nu^-1.6), radius-to-frequency mapping, polarization and the population of luminosities. Answer: a first-principles kinetic model reproducing these observables.

What would settle it

A kinetic model that predicts spectra, polarization and luminosity versus spin-down power matching population data from FAST and MeerKAT surveys.

Status in the literature

2020: kinetic simulations showed that nonstationary pair discharges at the polar cap emit coherent electromagnetic waves, a candidate mechanism now being tested against observed spectra.