It is often stated that pulsar timings are very stable and hence used as a cosmic clock by astronomers. Yet, on a live demonstration at Dwingaloo Observatory in Netherlands tonight, we saw that irregular missed beats occurred on the pulsations coming from the pulsar they observed.
Great question — and you didn’t imagine it. What you saw is exactly what pulsar astronomers expect in a live, single-pulse demo.
The key idea is this:
Pulsars are exquisitely stable clocks in the average, not pulse-by-pulse.
Here’s what’s going on.
1. The clock is in the rotation, not each radio flash
The neutron star’s rotation period is astonishingly stable — rivaling atomic clocks over long timescales. That’s what’s used for:
pulsar timing arrays
gravitational wave detection
tests of general relativity
But the radio emission mechanism is noisy and fickle.
When we say “a pulse every X milliseconds,” that’s shorthand for:
When you fold thousands to millions of rotations together, a stable profile emerges.
A live demo is usually showing individual pulses, not a folded profile — and individual pulses are messy beasts.
2. “Missed beats” are often intrinsic to the pulsar
Several well-known effects cause pulses to disappear or weaken:
🔹 Nulling
Some pulsars simply switch off their radio emission for one or more rotations:
lasts from a single pulse to seconds or minutes
the star is still rotating perfectly normally
emission mechanism temporarily stops
Classic, very common phenomenon.
🔹 Mode changing
The pulsar abruptly switches between emission states:
strong pulses → weak pulses → different pulse shape
looks like irregularity, but timing remains intact
🔹 Giant pulses vs weak pulses
Many pulsars emit:
occasional very strong pulses
many weak ones near the noise floor
In a live setup, the weak ones just vanish into the noise.
3. The interstellar medium actively messes with the signal
Between Dwingeloo and the pulsar lies a lot of turbulent plasma.
🌌 Interstellar scintillation
Think of it as cosmic twinkling, like stars in visible light:
constructive interference → strong pulses
destructive interference → pulses fade or vanish
timescale: seconds to minutes (exactly what you saw)
Nothing about the pulsar changed — the propagation did.