Pulsar LGM-1: Visualisation · Signals from the Periphery

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Pulsar

B1919+21

Period

1.3373 s

Sweeps Earth?

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Timing

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LGM-1 · PSR B1919+21
Mullard Radio Astronomy Observatory
Cambridge · found 28 Nov 1967
Jocelyn Bell · Antony Hewish · 81.5 MHz
P 1.3373 s · Vulpecula · ~2,300 ly
first filed, half in jest, as Little Green Men 1

Feature

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Evidence

fact ⇄ what kind of claim · live

The scruff: same sidereal time, day after day

Aug-Nov 1967 · a quarter inch in 96 ft/day

MEASURED

Pulses at 1.3373 s, stable to clock quality

28 Nov 1967 · the fast recording

MEASURED

Timing flat: no orbit, so no planet, so no LGM

Earth's own Doppler seen · the source's, absent

MEASURED

Four sources across the sky by January 1968

CP 1133, 0834, 0950 join CP 1919

MEASURED

This lighthouse: dipole + tilted beams + geometry

the pulse profile falls out of two angles

MODELLED

A rotating neutron star: settled by the 33 ms Crab

1968 · only a neutron star can turn that fast

MEASURED

LGM: the reading that was tested, then let go

Bell: "some silly lot of little green men"

READING

View

The pulsar

MEASURED · the first pulsar · Bell's scruff, 1.3373 s

playback ×1 · fast pulsars run in slow motion; the period shown is the real one

The timing test · what killed LGM

Anybody transmitting lives on a planet, and a planet orbits: its motion must stretch and squeeze the pulse period over the months, ΔP/P = v/c. The team found exactly one such wobble in the data, the Earth's own orbit, proving the source lay far outside the solar system, and beyond that, nothing. Flat timing, no planet, no LGM.

Geometry · aim the lighthouse

Magnetic inclination α45°

the tilt between the spin axis and the beams. Drag to zero and the pulses die: an aligned rotator blinks for nobody.

Viewing angle ζ50°

where Earth sits relative to the spin axis. If the sweeping cone never crosses this line, the pulsar shines and we never know. Most don't sweep us.

Overlays

Dipole field lines

Auto-play

Readout · live

Period P

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Slowdown Ṗ

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Characteristic age

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Beam width ρ

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Pulses caught

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Timing residual

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What is measured vs what is read

Measured: the charts and the scruff's sidereal clock, the 1.3373 s period, the flat timing residuals, the second sources, and the Crab's 33 ms. Modelled: this lighthouse drawing, the dipole field, the beam geometry. Reading: LGM was one, for a few honest weeks in 1967, and it was tested and retired. What remains is settled physics.

Where this drawing takes liberties

The star is drawn thousands of times too large, the beams are cartoons of a messy magnetosphere, and the fast pulsars run in slow motion so your eye can follow. The periods are real, B1919's rotation on screen is real-time, the two-angle geometry is the actual lighthouse model, and the pulse profile on the strip falls out of that geometry, not out of an animation.

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drag = orbit · scroll = zoom · click a label to inspect · aim the beam with the two angle sliders