The Gravitational Wave Optical Transient Observer

Tuesday 15th May, 2018

Our speaker was Dr Danny Steeghs from Warwick University who mentioned in his introduction that he had visited the Society about 10 years ago to give a talk about astrotomography. This is a method of analysing stars by taking a series of cross-sectional images and then using a computer to put them back together. The technique is more widely known in its use as a medical diagnosis tool in hospitals when it is referred to as a CT or CAT scan.

Dr Steeghs began the evening's talk, entitled "The Gravitational-wave Optical Transient Observer (GOTO)", by saying that astronomy had begun as a purely visual science using wavelengths of light that the human eye could see. As technology had progressed we are now able to examine objects such as our own galaxy in other wavelengths from long radio waves through to incredibly short gamma rays. Each observation in a particular wavelength reveals a different aspect of our home galaxy, the Milky Way. For example, the centre of our galaxy is obscured by dust but by observing in infrared light we can see into the central region.

He then continued by saying that only three years ago a different wave was employed to study the Universe — namely gravitational waves. These are not light waves but are actually ripples in the fabric of space-time itself. Just as a stone tossed into a pond sends water waves rippling away from its point of impact, so massive bodies in space send out gravitational waves as they move. In America and Italy incredibly sensitive gravitational wave detectors have been built called, respectively, LIGO and VIRGO and these have already detected mergers of black holes and neutron stars.

However, with only three observatories spread widely across the Northern Hemisphere, it is not possible to pinpoint exactly where on the sky these mergers came from. But this problem is what Dr Steeghs' international team of scientists is hoping to solve using a number of robotic telescopes that automatically scan large areas of the sky for the visual afterglow of a gravitational wave event. Unfortunately, Dr Steeghs said that the merger of two black holes would not give off any detectable light at visual wavelengths but the merger of two neutron stars would, and LIGO is currently being upgraded to detect these sort of collisions.

To detect the visual remnants of these mergers, the GOTO project is planning to build two small optical observatories on the island of La Palma and further observatories in Australia if funds allow. Each observatory will consist of a small clamshell dome housing an array of eight telescopes attached to a single robotic mount. The data from La Palma is ready to be fed back to Warwick University through a dedicated fibre optic link and they currently have one dome working with 4 operational telescopes. This summer they are hoping to add another 4 telescopes to complete this first observatory, ready for when LIGO comes back online in autumn later this year.