RESEARCH HIGHLIGHT: A new approach to rapidly localise gravitational waves

Artist’s illustration of a black hole and neutron star orbiting each other and about to merge, by Carl Knox, OzGrav-Swinburne University

​Multimessenger astronomy is an emerging field which aims to study astronomical objects using different ‘messengers’ or sources, like electromagnetic radiation (light), neutrinos and gravitational waves. This field gained enormous recognition after the joint detection of gravitational waves and gamma ray bursts in 2017. Gravitational waves can be used to identify the sky direction of an event in space and alert conventional telescopes to follow-up for other sources of radiation. However, following up on prompt emissions would require a rapid and accurate localisation of such events, which will be key for joint observations in the future.
 
The conventional method to accurately estimate the sky direction of gravitational waves is tedious—taking a few hours to days—while a faster online version needs only seconds. There is an emerging capacity from the LIGO-Virgo collaboration to detect gravitational waves from electromagnetic-bright binary coalescences, tens of seconds before their final merger, and provide alerts across the world. The goal is to coordinate prompt follow up observations with other telescopes around the globe to capture potential electromagnetic flashes within minutes from the mergers of two neutron stars, or a neutron star with a black hole—this was not possible before. The University of Western Australia’s SPIIR team is one of the world leaders in this area of research. Determining sky directions within seconds of a merger event is crucial,as most telescopes need to know where to point in the sky. In our recently accepted paper [1], led by three visiting students (undergraduate and Masters by research) at the OzGrav-UWA node, we applied analytical approximations to greatly reduce the computational time of the conventional localisation method while maintaining its accuracy. A similar semi-analytical approach has also been published in another recent study [2].
 
The results from this work show great potential and will be integrated into the SPIIR online pipeline going forward in the next observing run. We hope that this work complements other methods from the LIGO-Virgo collaboration and that it will be part of some exciting discoveries.
 
Written by OzGrav PhD student Manoj Kovalam, University of Western Australia.
 
[1] https://doi.org/10.1103/PhysRevD.104.104008
[2] https://doi.org/10.1103/PhysRevD.103.043011
This work is now accepted by PRD: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.104.104008