Gravitational Waves: Visualisation · Signals from the Periphery

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Source

GW150914

Frequency

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Strain h

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Magnified

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Polarisation

Circular

Gravitational Waves · LIGO
ΔL = ½ h L · strain h ~ 10⁻²¹
4 km arms · ΔL ~ 10⁻¹⁸ m
f_GW = 2 f_orbit · sweeps up: the chirp
GW150914 · 3 M☉ radiated · 1.3 Gly
14 Sep 2015 · Hanford & Livingston

Component

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Strain, live

ΔL = ½ h L

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Exaggeration (ring stretch)

magnified×10²⁰

View

Source

Established · First detection (2015)

Polarisation

Controls

Exaggeration44%

the real strain is ≈10⁻²¹, a thousandth of a proton across 4 km. Magnified so the pattern can be seen; the true h is always shown

Playback speed1.0×

the real GW150914 sweep lasted 0.2 s; slowed here so the eye can follow the chirp

Frequency (steady waves)200 Hz

only for the steady +, × and circular presets

Display

Spacetime grid / sheet

Ring of test masses

LIGO interferometer

Strain trace h(t)

Auto-rotate

Readout · live

Frequency f_GW

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True strain h

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Arm change ΔL

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Separation

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Chirp mass 𝓜

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Magnified

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Why the detector is an L

A wave stretches one direction while it squeezes the perpendicular one. Measure a single length and you cannot tell a wave from the mirror drifting; measure the difference between two arms at right angles and the two effects add. That is a Michelson interferometer: split a laser down two 4 km arms, bounce it back, recombine. When the arms fall out of step by 10⁻¹⁸ m the recombined light dims, and that dimming is the signal.

What is exact vs stylised

Exact: the +, × and circular patterns and the ring deformation ΔL = ½ h L; the chirp shape f ∝ τ⁻³ᐟ⁸ and A ∝ f²ᐟ³ through the inspiral; the detector's genuine blindness to × on x/y arms; and the GW150914 / GW170817 masses, distances and frequencies. Stylised: the merger and ringdown are sketched in the right spirit (the true merger needs numerical relativity); GW170817 is drawn at GW150914's peak strain, where its real peak was about a sixth of that, so the neutron-star pattern stays readable at the same magnification; the strain is magnified by the factor shown live; and the real sub-second sweep is slowed so the eye can follow it.

Strain h(t): what LIGO records · drag to scrub

blind to × in this orientation

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drag = orbit · scroll = zoom · click a part