Pulsars flicker because of electric funnels in their magnetic field ✛ ✎ ✦
A pulsar is a super-dense neutron star left over after a supernova explosion. It spins rapidly, holding a cloud of plasma with its magnetic field. The plasma rotates unevenly: faster near the axis than at the edges. This difference spawns electric funnels, like a whirlpool. They grow in just a few rotations of the star (which for an Earth observer stretch out due to the immense gravity). The funnels stir up charges and fling them toward the light cylinder — the outer boundary of the magnetosphere. There, particles disrupt the radio signal, causing the pulsar to flicker or fall silent altogether.
Astronomers detect these changes using spectroscopy: they break radio waves into frequencies, tracking how the funnels distort the emission. Now the variability of pulsars has a clear cause.
The strength of the electric funnel is just a couple percent of the pulsar's total charge, but that's enough to make this cosmic lighthouse flicker.
In Carl Sagan's 'Contact,' aliens turned a pulsar into a beacon; nature does just fine without them: electric funnels turn the star into a twinkling transmitter all on their own.