Guided sky tour · 7 stops · about 2 minutes

Gravitational waves

Einstein's ripples in space: how pulsars proved them, how LIGO hears them, and where they come from.

Take it on the live map

Sit back: it plays by itself. Space pauses, ← → move, reads it aloud.

The whole sky

Stop 1 of 7

Ripples in space itself

Gravitational waves are ripples in space, sent out when black holes or neutron stars spiral together. LIGO, Virgo and KAGRA measure them as a stretch of less than a thousandth of a proton's width. Each shaded patch is where a recent event came from: one detection narrows a source only to a patch of sky.

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Hulse-Taylor Pulsar: a sky-survey photograph of its field

Hulse-Taylor Pulsar · 21,000 light-years

Stop 2 of 7

The first proof

In 1974 Russell Hulse and Joseph Taylor found this pair of neutron stars, orbiting each other every 7.75 hours. Their orbit shrinks exactly as Einstein predicted if they lose energy to gravitational waves, which won the 1993 Nobel Prize.

21,000 light-years light left 21,000 years ago

Explore it on the map Hulse-Taylor Pulsar's page

Double Pulsar: a sky-survey photograph of its field

Double Pulsar · 2,400 light-years

Stop 3 of 7

Two pulsars at once

The Double Pulsar, found in 2003, is the only known pair in which both neutron stars are pulsars. Timing it tests Einstein's theory more precisely than anything else; the two will merge in about 85 million years.

2,400 light-years light left 2,400 years ago, around 375 BC

Explore it on the map Double Pulsar's page

Cygnus X-1: a sky-survey photograph of its field

Cygnus X-1 · 7,200 light-years

Stop 4 of 7

The first black hole merger

Most events are pairs of black holes like the one in Cygnus X-1. The first, GW150914 in September 2015, came from black holes of about 36 and 29 Suns merging 1.3 billion light-years away: three Suns' worth of mass turned into gravitational waves in a fraction of a second.

7,200 light-years light left 7,200 years ago, around 5,175 BC

Explore it on the map Cygnus X-1's page

NGC 4993 (GW170817): a sky-survey photograph of its field

NGC 4993 (GW170817) · 130 million light-years

Stop 5 of 7

Heard and seen

GW170817 was the first event seen in light too: two neutron stars merging in NGC 4993. It showed that gravitational waves travel at the speed of light and that such mergers forge much of the universe's gold.

130 million light-years light left 130 million years ago

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PSR J0437-4715: a sky-survey photograph of its field

PSR J0437-4715 · 510 light-years

Stop 6 of 7

A galaxy-sized detector

Slower waves, from pairs of giant black holes, need a detector the size of the galaxy. Pulsar timing arrays time dozens of millisecond pulsars like this one; in 2023 they reported the first signs of a background hum of such waves.

510 light-years light left 510 years ago, around AD 1516

Explore it on the map PSR J0437-4715's page

M87* (Messier 87): a sky-survey photograph of its field

M87* (Messier 87) · 53 million light-years

Stop 7 of 7

Giants that make the hum

M87*, the first black hole ever photographed (2019), weighs about 6.5 billion Suns. Pairs of black holes this big, brought together when their galaxies collide, are thought to make that hum.

53 million light-years light left 53 million years ago

Explore it on the map M87* (Messier 87)'s page

Tour complete

Gravitational waves

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