STARS COLLIDE ...
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 USbased 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, infra-red 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.
“These extremely small and dense objects are the remains of giant stars 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 detectable gravitational waves when they merge,” Cunnama said.
The first detection of gravitational waves, made on September 14, 2015 and announced on February 11, 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.
Petri Vaisanen, Head of SALT Astronomy Operations, who was the observer stationed at the SALT telescope, said August 18 – the day after the LIGO detection – was a busy day in the Karoo.
“After a flurry of messages and e-mails that afternoon in Sutherland, I finally got the co-ordinates. 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,” Vaisanen concluded.