South African researchers have been part of a massive international effort to observe the collision of two neutron stars, after astronomers at the US-based Laser Interferometer Gravitational Wave Observatory (LIGO) and the European-based Virgo detector spotted gravitational waves coming from this cataclysmic event in a galaxy 130-million light years away.

Gravitational waves are ripples in the fabric of space-time, and although they were predicted by Albert Einstein in 1916 they were only detected for the first time two years ago, by scientists at LIGO who this year won the Nobel Prize for physics.

Since then there have been three more gravitational wave observations, but they have all been produced when black holes spiraled into each other, emitting no light. Monday’s announcement, which took simultaneously at several locations around the world, marks the first time astronomers have observed gravitational waves and electromagnetic radiation coming from the same event.

Petri Vaisanen, head of astronomy operations at the South African Large Telescope (SALT), said the discovery provided such an enormous amount of new information that it was like gaining an extra sense.

Southern African Large Telescope at Sutherland. Picture: SALT Foundation
Southern African Large Telescope at Sutherland. Picture: SALT Foundation

"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.

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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