Australia’s new eyes on the skies to look for gravitational wave events

Australia will soon be the southern hemisphere’s eyes-on-the-skies when it comes to searching for the optical wavelength after-effects of some of the most violent collisions and mergers in our Universe. 

A new instrument, known as the Gravitational-wave Optical Transient Observer (GOTO) is set to be built at one of Australia’s most iconic dark sky regions, the Siding Spring Observatory - located in north, central NSW. 

The instrument is made of two autonomous telescope mount systems, each featuring eight individual 40-centimetre telescopes that cover a very large region of the sky, utilising the light collecting power of a combined array of 16 astrographs, and giving a powerful 800 million pixel output. 

The new GOTO instrument in development in Australia will be the second of its kind, with the first already developed and operating in La Palma, in Spain’s Canary Islands. The vision is to position each of these telescopes in their own hemispheres to provide entire sky coverage, both north and south. 

“This is really encouraging from an international cooperation perspective that the UK is willing to support this project, with new telescopes to be built in Australia,” said Associate Professor (A/Prof) Duncan Galloway, from the Monash University School of Physics and Astronomy.

What GOTO will be looking out for is the electromagnetic counterpart signal that emerges when very high mass objects, like binary pairs of neutron stars, follow inspiral orbits, eventually merging in a huge explosion known as a kilonova. The light from these explosions is very important to astronomers, as its signature contains information about how some of the heaviest elements in the Universe - like gold and platinum - are created. 

But what triggers GOTO to search for these signals doesn’t come from the explosion in space itself at first, as it would be very difficult (or extremely lucky) to be pointing any telescope at the exact patch of sky when one of these explosions goes off. Instead, from data and information come from another, terrestrial-based set of instruments - the gravitational wave (GW) interferometers, like LIGO, VIRGO and KAGRA.

The GW detectors use giant lasers to observe passing gravitational waves, causing the perpendicular lasers to expand and shrink in their respective configurations. This occurs because as a gravitational wave passes through our region of the Solar System, it causes all matter  -you, me, the Earth and the interferometers - to be stretched and squeezed. 

Since the introduction of two additional detectors - VIRGO (located in Pisa, Italy) and KAGRA (located in Japan), as well as the two originals in two separate locations in the USA, astrophysicists have been able to get a better handle on the rough location of where a GW event originates from, in the sky. But for the most part, it’s still a big patch of sky that contains hundreds of thousands, or millions of galaxies from which these events could occur. 

And this is where GOTO steps in, to fill an observational gap in hopefully helping track down any counterpart light signal from the kilonova, based on where the GW detectors say it is coming from. And then, where a potential electromagnetic signal has been detected, GOTO will notify astronomers and observatories all around the world, so that they can quickly turn their instruments to the source and begin collecting data. 

As the light from kilonovas changes rapidly, astronomers are in a race against time to get these instruments looking in the right direction, as soon as possible to get the most data from these violent events - allowing a proper scientific analysis that uses a multi-messenger methodology that combines information from the GW event, as well as the electromagnetic event. 

In 2017, the world was treated to the first of these types of events, when two neutron stars merged, emitting gravitational radiation that was detected by the GW interferometers. The localisation of this event was reasonable, which then allowed electromagnetic telescopes to look into the expected region - and there it was - the light from the kilonova. This event became known as the GW170817 event and has been studied extensively. 

“The new site gives us a massive improvement in our chance to observe the counterparts of Gravitational Wave detections. Detecting the optical counterparts promptly is a key factor in how much we can learn from Gravitational Wave detections. The first such event, GW170817, was identified in 11 hours; but our GOTO network can be on sky and autonomously observing the field within minutes,” said A/Prof. Galloway. 

Along with the telescope being built at the Siding Spring Observatory, several astronomers and researchers from Monash University are also involved in the project, which also features a number of international organisations, including the lead institution, the University of Warwick. 

“There are fleets of telescopes all over the world available to look towards the skies when Gravitational Waves are detected, in order to find out more about the source. But as the Gravitational Wave detectors are not able to pinpoint where the ripples come from, these telescopes do not know where to look,” said Professor Danny Steeghs of the University of Warwick, GOTO’s Principle Investigator.

“The award of £3.2 million of STFC funding was critical in allowing us to build GOTO, as it was always envisaged to be; arrays of wide-field optical telescopes in at least two sites so that these could patrol and search the optical sky regularly and rapidly.”

“This will allow GOTO to provide that much-needed link, to give the targets for bigger telescopes to point towards,” he said. 

The robotic systems that control the telescope are expected to operate autonomously, patrolling the sky continuously but also focusing on particular events or regions of sky in response to alerts of potential Gravitational Wave events.