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SA telescopes track neutron star collision

SA telescopes track neutron star collision

The astronomical facilities of the National Research Foundation of South Africa (NRF) have contributed to the study of what is fast becoming one of the most widely studied events in the history of astrophysics.
These events are a direct detection of gravitational waves — ripples in space and time — from the collision of two neutron stars.

The international LIGO and Virgo collaborations have announced the first detection of gravitational waves produced by two colliding neutron stars. Through investigations of more than 70 astronomical facilities worldwide and in Earth orbit, this is also the first time that gravitational waves (ripples in space-time) and light (electromagnetic waves) have been observed from the same object, opening a new window into a deeper understanding of the cosmos.

The Southern African Large Telescope (SALT), and numerous telescopes hosted at the South African Astronomical Observatory (SAAO) Sutherland site, observed the event just over a day after the gravitational wave had passed through the Earth on 17 August 2017.

A telescope in Chile first detected light from the merger of the two neutron stars in a galaxy 130-million light years from Earth. As soon as it was dark enough that evening in South Africa, SALT and other telescopes started observing the optical counterpart of the gravitational waves event dubbed GW170817.

Early observations in this case were very important, because the optical “afterglow” from the collision varies rapidly, becoming dimmer and changing in colour.

The large complement of sensitive telescopes and instruments available in Sutherland allowed some crucial measurement to be done that will contribute to a better understanding of this remarkable event. This work will be presented in numerous articles to be published in international astronomical journals starting today.

Radio emission is expected from the fast-moving debris resulting from the merger of the two neutron stars heralded by GW170817.

SKA South Africa’s MeerKAT telescope (part of the South African Radio Astronomy Observatory) has observed the location of the merger on three dates since late August. So far it hasn’t detected a signal, despite very sensitive observations.

SARAO’s HartRAO also participated in observations of this event through its inclusion in an international network of radio telescopes.
While the aftermath of GW170817 initially dimmed quickly in visible light, it is expected to get brighter over the coming weeks at radio wavelengths.

The partially-built MeerKAT is already one of the world’s most sensitive telescopes of its kind, and upcoming observations will continue to monitor this extraordinary cosmic event.

Dr Molapo Qhobela, CEO of the NRF, comments: “We congratulate the astronomy research facilities for the important role that they played in this unprecedented astronomical event.

“The quality of the facilities, including their ability to respond rapidly to fast-evolving events, and the connections developed by local researchers with their counterparts around the world, has allowed South Africa to play a meaningful role in the event announcing the birth of the new era of multi-messenger astronomy.

“The NRF looks forward to further discoveries in this new domain, and to ever greater participation of its facilities and the researchers of South Africa in these exciting endeavours.”

Time-domain astronomy, the study of the variable cosmos, is at the forefront of astrophysical research. With the coming availability of MeerKAT; with the novel MeerLICHT optical telescope in Sutherland that will simultaneously observe whatever MeerKAT is observing at radio wavelengths; with SAAO’s plans to make time-domain astronomy one of its focus areas; and with the recently secured access for South African researchers to the Large Synoptic Survey Telescope (LSST), set to become in the next decade the world’s premier time-domain optical facility, the future for South African contributions in this area is indeed bright.


Pictured: The hot, dense, expanding cloud of debris stripped from two neutron stars just before they collided. Within this neutron-rich debris, large quantities of some of the universe’s heaviest elements were forged, including hundreds of Earth masses of gold and platinum.

This represents the first time scientists detected light tied to a gravitational-wave event, thanks to two merging neutron stars in the galaxy NGC 4993, located about 130 million light-years from Earth in the constellation Hydra.

Image Credit: NASA Goddard Space Flight Center/CI Lab