Neutron-Star Merger (GW170817)
On 17 August 2017 LIGO and Virgo heard two neutron stars merge; 1.7 seconds later telescopes saw a gamma-ray burst, then the glow. It was the first multi-messenger event and showed where gold comes from.
Open in the interactive tree →The signal came from the galaxy NGC 4993, about 130 million light-years away. Fermi detected a gamma-ray burst 1.7 s after the merger, and an optical counterpart (AT 2017gfo) was found about 11 hours later, followed by many telescopes worldwide. The fading glow matched a kilonova, the light of freshly made heavy elements; one estimate is about 10 Earth masses of gold and platinum. The event gave an independent Hubble constant of about 70 km/s/Mpc (+12, -8), limited any difference between the speeds of gravity and light to a few parts in 10^15, and Science named it the 2017 Breakthrough of the Year.
Prerequisites
- Nuclear Physics1938Heavy elements form by rapid neutron capture, a nuclear process
- Pulsars1967Neutron stars were known from pulsars, including the binary pulsar that loses orbital energy
- Gravitational Waves Detected2015LIGO and Virgo's laser interferometers detected the signal
Unlocks
- Dark Energy & Hubble TensionopenA merger seen in gravity and light gave a Hubble constant independent of both sides