17 October 2017

South Africa: SA Telescopes Observe Gravitational Waves From Collision of Two Stars

South African scientists have announced that two local telescopes have for the first time detected gravitational waves that are a result of a merging of two neutron stars.

The two telescopes are the South African Astronomical Observatory (SAAO) in Cape Town and the Southern African Large Telescope (SALT) in the small Karoo town of Sutherland.

According to previous research, the neutron stars - which are the smallest and densest known stars - collided 130 million light years ago, an event that resulted in gravitational waves being emitted and detectible for 100 seconds.

In an interview shortly after the announcement at the SAAO headquarters in Observatory, Cape Town, on Monday afternoon, Dr Daniel Cunnama, a ‎Postdoctoral Research Fellow at the South African Astronomical Observatory, said the detection, which happened on August 17, was very significant for astrophysics.

"Why we are here today is basically we have for the first time detected gravitational waves and electro-magnetic radiation, or light, from the same event [the merging of the two neutron stars]... and we have managed to follow up this event with South African telescopes in Sutherland. Multiple telescopes contributed to the understanding of this astronomical event," he said.

Leading up to the detection, a total of about 4 000 scientists and astronomical researchers from observatories, universities and other institutions from around the world and many in South Africa collaborated in the research.

Seven papers have come out from the South African Astronomical Observatory around this event already. Over 70 observatories were included in this observing campaign.

"The original detection was made in the United States, along with the European Space Observatory as well as many others that were involved.

"It is a great day for South African astronomy. We have shown ourselves to be able to contribute valuably to an international endeavour.

"We have world class telescopes here, which we have managed to set up over the last 20 years and we can really do wonders for future science such as this," said Cunnama.

The collision of the neutron stars

About 130 million light years ago, in a distant galaxy, two incredibly dense objects, known as neutron starts, merged together in a cataclysmic explosion.

According to astronomers, this event was so violent that it destroyed the very fabric of space in time.

The effects of that explosion travelled at the speed of light and reached earth on August 16 of this year and were detected by US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European-based Virgo detector.

Subsequent observations by SALT and other telescopes in Sutherland have played a similar role in understanding that event. For the first time, local astronomers have been able to identify and study the source of the gravitational wave event.

The collision also resulted in an explosion of light, initially in the form of gamma rays, which were detected by space-based telescopes. The gamma rays were then followed by X-rays, ultraviolet, optical, infrared and radio waves.

This allowed astronomers to localise the event within hours and launch follow-up observations by SALT and numerous other telescopes in South Africa and around the world.

Making an announcement earlier on, Cunnama said: "These extremely small and dense objects are the remains of giant starts that have exploded at super nova and more mass than the sun is compressed into a sphere that is about the size of a city. These neutron stars are commonly found in pairs and Einstein's general relativity predicts that these incredibly large objects should produce detectible gravitational waves when they merge."

The first detection of gravitational waves, made on 14 September 2015 and announced on 11 February 2016, was a milestone in physics and astronomy. It confirmed a major prediction of Albert Einstein's 1915 general theory of relativity, and marked the beginning of the new field of gravitational-wave astronomy.

Ever since the first detection, there have been three more detections confirmed.

On 3 October, the three leaders of the research - physicists Rainer Weiss of the Massachusetts Institute of Technology and Barry Barish and Kip Thorne of the California Institute of Technology - were awarded the 2017 Nobel Prize in Physics for their work on gravitational waves.

Petri Vaisanen, Head of SALT Astronomy Operations, who was the observer stationed at the SALT telescope, said on August 18 -- the day after the LIGO detection -- was a busy day at the Karoo.

"After a flurry of messages and emails that afternoon in Sutherland, I finally got the coordinates.

"There was a new object, which had caused the whole of space-time to ripple, sitting at the outskirts of the galaxy NGC 4993, some 130 million light years away.

"I knew that everyone with a working telescope in the Southern Hemisphere was scrambling to get data on it. We decided to drop all other plans for that evening, and went for a spectral observation with SALT, since you need a large telescope for such observations breaking up the light into all its colours.

"It was a difficult observation since we had to do it in twilight, before it got properly dark. I'm very proud of the whole team. SALT was only the third observatory to provide a spectrum of the target, and the first spectrum that clearly started showing anomalous behaviour proving that this was no run-of-the-mill transient event."

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