New telescope to be the ’GOTO’ for gravitational wave events

GOTO Telescop image credit - STFC
GOTO Telescop image credit - STFC

A new telescope, made up of two identical arrays on opposite sides of the planet, will track down sources of gravitational waves.

The Gravitational-wave Optical Transient Observer (GOTO) will help shepherd in a new era of gravitational wave science. Deployed across two antipodal locations to fully cover the sky, GOTO will scour the skies for optical clues about the violent cosmic events that create ripples in the fabric of space itself.

GOTO began when the UK’s University of Warwick and Australia’s Monash University wanted to address the gap between gravitational wave (GW) detectors and electromagnetic signals. Now the international collaboration has 10 partners, 6 of which are in the UK.

The primary science of GOTO is to detect the optical light connected to gravitational wave events. As part of the overall GOTO activity, The University of Manchester will be using the new telescope to help its astronomers search for unique ’spider’ pulsars, the name for very fast spinning binary pulsars.

For the gravitational wave science, GOTO needs to scan a large area of the sky repeatedly, both to find these events as they occur but also to build a very accurate reference of what the sky ’normally’ looks like so that if a gravitational wave counterpart appears one can tell it was not there before. The ability of GOTO will allow researchers to produce extended time-lapses of the sky, which can then be mined for all kinds of other variable sources.

Professor Rene Breton of The University of Manchester , one of the GOTO project partners, says that the science return also goes beyond gravitational waves. "The ’time-lapse’ picture of the sky it continuously builds up is a gold mine to study variability in other astronomical objects and search for transient phenomena unconnected to gravitational wave events," he said.

The ’time-lapse’ picture of the sky it continuously builds up is a gold mine to study variability in other astronomical objects and search for transient phenomena unconnected to gravitational wave events.

"In our specific case, we’re after discovering new spider pulsars by looking for the periodic signature of the heated star orbiting them. Some display unexpected changes and brighten up as mass suddenly start flowing from the companion star towards the pulsar. We don’t understand this behaviour as it occurs quickly (somewhere between days to weeks) and has only been observed a couple of times. Having "eyes" scanning the sky is exactly what we think could help us uncover their secrets."

GOTO has received 3.2 million of funding from the Science and Technology Facilities Council (STFC) to deploy the full-scale facility.

Long hypothesised as a by-product of the collision and merger of cosmic behemoths such as neutron stars and black holes, gravitational waves were finally detected directly by the Advanced LIGO (Laser Interferometry Gravitational-wave Observatory) in 2015.

GOTO is designed to fill this observational gap by searching for optical signals in the electromagnetic spectrum that might indicate the source of the GW - quickly locating the source and using that information to direct a fleet of telescopes, satellites and instruments at it.

As most GW signals involve the merger of massive objects, these ’visual’ cues are extremely fleeting as must be located as quickly as possible, which is where GOTO comes in.

The idea is that GOTO will act as sort of intermediary between the likes of LIGO, which detect the presence of a gravitational wave event, and more targetable multi-wavelength observatories that can study the event’s optical source.

Professor Danny Steeghs of the University of Warwick, GOTO’s Principle Investigator, said: "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."

"If the gravitational wave observatories are the ears, picking up the sounds of the events, and the telescopes are the eyes, ready to view the event in all the wavelengths, then GOTO is the bit in the middle, telling the eyes where to look."

Following the successful testing of a prototype system in La Palma, in Spain’s Canary Islands, the project is deploying a much expanded, second generation instrument.

Two telescope mount systems, each made up of eight individual 40 cm (16 inch) telescopes, are now operational in La Palma. Combined, these 16 telescopes cover a very large field of view with 800 million pixels across their digital sensors, enabling the array to sweep the visible sky every few nights.

These robotic systems will 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.

In parallel, the team is preparing a site at Australia’s Siding Spring Observatory, which will contain the same two-mount, 16 telescope system as the La Palma installation.

The plan is to have both sites operational this year to be ready for the next observing run of the LIGO/Virgo gravitational wave detectors in 2023.

The optical search for gravitational wave events is the next step in the evolution of gravitational wave astronomy. It has been achieved once before, but with GOTO’s help it should become much easier.

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