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A New Approach To Rapidly Localize Gravitational Waves To Coordinate Prompt Follow-Up Observations

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

Multimessenger astronomy is an emerging field that aims to study astronomical objects using different ‘messengers’ or sources, like electromagnetic radiation (light), neutrinos, and gravitational wavesGravitational waves are distortions or ripples in the fabric of space and time. They were first detected in 2015 by the Advanced LIGO detectors and are produced by catastrophic events such as colliding black holes, supernovae, or merging neutron stars.”>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 localization 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 LIGOThe Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory supported by the National Science Foundation and operated by Caltech and MIT. It’s designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. It’s multi-kilometer-scale gravitational wave detectors use laser interferometry to measure the minute ripples in space-time caused by passing gravitational waves. It consists of two widely separated interferometers within the United States—one in Hanford, Washington and the other in Livingston, Louisiana.”>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 starA neutron star is the collapsed core of a large (between 10 and 29 solar masses) star. Neutron stars are the smallest and densest stars known to exist. Though neutron stars typically have a radius on the order of just 10 – 20 kilometers (6 – 12 miles), they can have masses of about 1.3 – 2.5 that of the Sun.”>neutron star with a black holeA black hole is a place in space where the pull of gravity is so strong not even light can escape it. Astronomers classify black holes into three categories by size: miniature, stellar, and supermassive black holes. Miniature black holes could have a mass smaller than our Sun and supermassive black holes could have a mass equivalent to billions of our Sun.”>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 localization method while maintaining its accuracyHow close the measured value conforms to the correct value.”>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. “Semianalytical approach for sky localization of gravitational waves” by Qian Hu, Cong Zhou, Jhao-Hong Peng, Linqing Wen, Qi Chu and Manoj Kovalam, 3 November 2021, Physical Review D.
    DOI: 10.1103/PhysRevD.104.104008
  2. “High speed source localization in searches for gravitational waves from compact object collisions” by Takuya Tsutsui, Kipp Cannon and Leo Tsukada, 22 February 2021, Physical Review D.
    DOI: 10.1103/PhysRevD.103.043011

Source: SciTechDaily