Two neutron stars collide — and the explosion stuns astronomers

“Imagine all your life you have merely looked at the world. Two years ago you heard voices coming from somewhere around you. Then suddenly, you actually see someone talking. How much more will you understand about how the world looks when you put those together? That to me sums up the momentous discovery and hints at the possibilities going forward,” said Petri Vaisanen, head of operations at the South African Large Telescope (SALT), which contributed to the spectral observations of the event. SALT was one of the telescopes that observed the colour of the neutron star merger, which went from blue to red.

LIGO and Virgo detected the gravitational waves on August 17, triggering 70 land and space-based observatories to train their telescopes on the region in which they had detected the neutron star collision. These instruments detected a gamma ray burst in the same part of the sky two seconds later, and then gathered large amounts of data on the event from x-rays, ultra-violet, optical light, infra-red, and radio waves.

Their work, published today in a series of articles in the journal Nature, has confirmed theoretical work showing that an initial neutron star collision is followed by an explosion called a kilonova, which blows heavy elements like gold and lead far out into space. The work also confirms the Hubble constant, which measures the rate at which the universe is expanding.

“This is the start of the new multi-messenger astronomy, where various techniques such as the gravitational wave laser interferometers… and astronomical techniques are used together to study one event,” said Sergio Colafranco, who led a team at the University of the Witwatersrand that worked with data from the High Energy Spectroscopic System telescope in Namibia and the AGILE system in Italy.

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The MeerKAT radio telescope under construction in the Karoo, and several optical telescopes managed by the South African Astronomical Observatory were also involved in observing the event, which scientists have dubbed GW178017.

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