A global team of scientists, including researchers from The University of Western Australia, has witnessed the death spiral and merger of a neutron star and a black hole, rare space events that likely took place a billion years ago, long before dinosaurs existed.
Although the events took place a long time ago, gravitational waves from these events have only just reached Earth.
"Many pairs of neutron stars have been found, but never a neutron star orbiting a black hole."
UWA Engineering Masters student Victor Oloworaran
The scientists detected them through the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US, and the Virgo gravitational-wave observatory in Italy.
The SPIIR (Summed Parallel Infinite Impulse Response) pipeline, developed by scientists at UWA, is one of five data analysis pipelines in the world that can analyse data from LIGO and Virgo in real-time and alert the public and astronomers within seconds of gravitational wave events being detected.
OzGrav ARC Centre of Excellence for Gravitational Wave Discovery UWA Postdoctoral Researcher Dr Fiona Panther said neutron stars were collapsed massive stars, and black holes were regions of space and time where gravity was so strong that nothing – not even particles or electromagnetic radiation such as light – could escape from it.
"The collision of the two results in the neutron star being ripped apart and swallowed by the black hole; a process that emits gravitational waves and may lead to the emission of light. This discovery will allow researchers to better understand the nature of space-time, and the building blocks of matter," Dr Panther said.
The first observation was made on 5 January 2020, when gravitational waves -- tiny ripples in the fabric of space and time -- were detected from the collision event by LIGO and Virgo. Detailed analysis of the gravitational waves revealed that the neutron star was around twice as large as the Sun, while the black hole was around nine times the size of the Sun. UWA's SPIIR pipeline detected the event less than a minute after the gravitational waves reached Earth.
Then, remarkably, on 15 January 2020 another merger of a neutron star and a black hole was observed from gravitational waves. This neutron star and black hole also collided around a billion years ago, but it was slightly smaller – the neutron star was around one-and-a-half times the size of the Sun, while the black hole was around five-and-a-half times the size.
The Zadko telescope at UWA was one of the Australian facilities that helped with the search effort for a counterpart to the merger event, led by UWA's Dr Bruce Gendre and Eloise Moore. Despite no optical counterpart detected, the observations helped constrain the physics at play during the merging phase.
UWA Engineering Masters student Victor Oloworaran, who was involved in the project and played a key role assisting the UWA team in analysing data to detect gravitational waves, said neutron stars and black holes had been predicted to exist by theorists for decades, but had long avoided detection.
"Many pairs of neutron stars have been found, but never a neutron star orbiting a black hole," he said.
"The detection of the neutron star-black hole merger is not only significant due to it being the world's first detection of this event, but it's also important as it shows that UWA's SPIIR pipeline gravitational waves detection system will be able to detect these events in future.
"It is a very exciting time in gravitational-wave astronomy right now, and between ongoing research and the use of emerging technologies, I can't wait to see what we achieve next."
Further information
UWA's contributions to the international effort in gravitational wave detection and follow-up observations include instrumentation (led by Professors Li Ju and Chunnong Zhao), online real-time detection (led by Professor Linqing Wen and Research Fellow Dr Qi Chu), and optical follow-up observations with the Zadko telescope (led by Professor David Coward and Dr Bruce Gendre).
The ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) is funded by the Australian Government through the Australian Research Council Centres of Excellence funding scheme. OzGrav is a partnership between Swinburne University of Technology (host of OzGrav headquarters), the Australian National University, Monash University, University of Adelaide, the University of Melbourne, and the University of Western Australia, along with other collaborating organisations in Australia and overseas.
LIGO is funded by NSF and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. Nearly 1300 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.php.
The Virgo Collaboration is currently composed of approximately 350 scientists, engineers, and technicians from about 70 institutes from Belgium, France, Germany, Hungary, Italy, the Netherlands, Poland, and Spain. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and Nikhef in the Netherlands. A list of the Virgo Collaboration members can be found at http://public.virgo-gw.eu/the-virgo-collaboration.
