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CUHK’s research advances the world’s first discovery of multi-messenger gravitational lensing
The Chinese University of Hong Kong (CUHK) is at the forefront of multi-messenger astronomy, pioneering global research that integrates gravitational waves, light and neutrinos to unravel cosmic mysteries. Led by Professor Otto Hannuksela from the Department of Physics, CUHK’s gravitational-wave group is driving international efforts to achieve the first detection of a lensed multi-messenger event. With the LIGO-Virgo-Kagra[1](LVK) collaboration’s fourth observing run underway and instruments such as the Legacy Survey of Space and Time (LSST)[2] and Euclid[3] opening new doors in astronomy, the 2024 Theo Murphy Royal Society Discussion Meeting on multi-messenger lensing brought scientists from across this emerging field together to discuss the challenges and opportunities. The meeting culminated in a comprehensive themed issue of leading scientific journal Philosophical Transactions A, with Professor Hannuksela’s gravitational-wave group contributing four out of the 16 research papers, highlighting the University’s pivotal role in advancing this transformative physics research.
The mystery of the cosmic magnifying glass
Gravitational lensing occurs when light or gravitational waves from distant celestial objects pass near massive galaxies and their paths are bent as if passing through a magnifying glass. While instruments like the Hubble Space Telescope have long observed the bending of light, CUHK researchers are pioneering the study of lensed gravitational waves.
The CUHK team’s role in the LVK international gravitational wave detection collaboration focuses on analysing gravitational wave data from binary black hole mergers to look for indicators of gravitational lensing effects, including waveform distortions and repeated signals. Successfully detecting the first lensed gravitational wave event could help identify the galaxy lensing system responsible for the merger event and allow observation of multiple signals from the same event. Such lensing localisation would constitute the only method to locate merging black holes with high precision. If the event is accompanied by an electromagnetic counterpart, as is the case when the source is a binary neutron star instead of a black hole, it would enable new studies across fundamental physics, astrophysics and cosmology.
Professor Hannuksela said: “The synergy between gravitational waves and electromagnetic observations opens entirely new avenues for cosmology. The contributions from CUHK reflect the institution’s commitment to addressing fundamental questions about the nature of gravity, dark matter and the formation of compact objects in our universe.”
First discovery expected within a decade
The LVK’s fourth observing run (O4), underway now, is expected to yield hundreds of gravitational-wave detections, with CUHK playing a critical role in data analysis. Collaborating with institutions such as ICG Portsmouth, UCLouvain, the University of Groningen, the Dutch National Institute for Subatomic Physics (Nikhef) and Utrecht University, the team will use CUHK’s unique methodology to localise lensed binary black holes by searching for multiple images and waveform distortions, and forecasting the expected types of lensed gravitational-wave events, as well as localising these events once they are detected.
The scientific community is in widespread agreement that the first discovery of multi-messenger gravitational lensing is likely within the next decade, with preparatory work required over the next three to five years. While challenges remain, the special themed issue of Philosophical Transactions A about multi-messenger astronomy is expected to bridge the gap between communities and revitalise efforts to address these obstacles through a united approach to achieving the first detection.
By the 2030s, next-generation detectors like the Einstein Telescope and Cosmic Explorer might bring even greater discovery potential. On the electromagnetic side, upcoming instruments like Euclid, the Vera C. Rubin Observatory’s LSST, and the Square Kilometre Array (SKA)[4] will further expand the search for multi-messenger lensing.
Professor Hannuksela and his team, including PhD students in CUHK’s Department of Physics Laura Uronen, Hemantakumar Phurailatpam and Jason Poon Sheung-chi, co-authored key sections of the themed issue, highlighting LVK science and black hole multi-messenger applications.
About multi-messenger astronomy
In astronomy, “multi-messenger” refers to the use of different types of cosmic signal, or messenger, to study astronomical events and objects. These messengers include gravitational waves, electromagnetic radiation and neutrinos. The 2017 discovery of the binary neutron star merger GW170817 by LIGO-Virgo marked the dawn of multi-messenger astronomy. In 2024, the Theo Murphy Royal Society Discussion Meeting brought together global experts to address challenges and opportunities in detecting lensed multi-messenger events, where gravitational waves and light are bent by massive cosmic objects, creating multiple images and a plethora of other signatures.
About The Chinese University of Hong Kong
Founded in 1963, The Chinese University of Hong Kong (CUHK) is a leading comprehensive research university with a global reputation and world-leading rankings. Located in the heart of Asia, CUHK has a vision and a mission to combine tradition with modernity, and to bring together China and the West. Under the University’s unique collegiate system, the programmes and activities offered by its nine colleges complement the formal curricula by delivering whole-person education and pastoral care. The University has eight faculties: Arts, Business Administration, Education, Engineering, Law, Medicine, Science, and Social Science. Together with the Graduate School, the University offers over 300 undergraduate and postgraduate programmes. All faculties are actively engaged in research in a wide range of disciplines, with an array of research institutes and research centres specialising in interdisciplinary research of the highest quality.
The University has been committed to promoting innovative technology and currently has more than 2,400 granted patents in different jurisdictions worldwide. Some of these patents have been licensed to relevant industries that help bring these innovations to the market to benefit society. In the 2024-25 academic year, CUHK has received 425 granted patents and filed 575 patent applications for inventions developed in the areas of medical technology, biotechnology, information technology, telecommunications, and materials science.
For the full research, please visit:
https://royalsocietypublishing.org/doi/10.1098/rsta.2024.0134
https://royalsocietypublishing.org/doi/10.1098/rsta.2024.0129
https://royalsocietypublishing.org/doi/10.1098/rsta.2024.0152
https://royalsocietypublishing.org/doi/10.1098/rsta.2024.0127
[1] LIGO – Laser Interferometer Gravitational-Wave Observatory; Virgo – Virgo Interferometer; Kagra – Kamioka Gravitational Wave Detector.
[2] Large Synoptic Survey Telescope (LSST) is an astronomical observatory in Coquimbo Region, Chile. Its main task is to conduct an astronomical survey of the southern sky every few nights, creating a ten-year time-lapse record.
[3] Euclid is a wide-angle space telescope with a 600-megapixel camera to record visible light, a near-infrared spectrometer, and photometer, to determine the redshift of detected galaxies.
[4] The Square Kilometre Array (SKA) is an intergovernmental international radio telescope project, it offers the view of the Milky Way galaxy is the best and radio interference is at its least.
The idea behind multi-messenger localisation of merging binary black holes is to locate the galaxy lens system that produced the merger observed with LVK through gravitational waves. A successful localisation would enable studies of multi-messenger lensing with merging black holes and would constitute the most precise localisation of these dark objects.
Image credits: Laura Uronen
Numerical simulation of a binary neutron star merger.
Besides binary black holes, binary neutron stars can also be used to study multi-messenger lensing. After these objects merge, they produce a burst of electromagnetic radiation that can be observed using telescopes. If a lensed version of these objects were observed, it would open a plethora of lines of enquiry across fundamental physics, cosmology and astrophysics.
Image credits: LVK
Illustration of gravitational lensing of compact object binaries.
The first lensed gravitational wave has been forecast to become observable by several independent groups across the globe, with about one in a thousand being such lensed binary compact objects. As detector sensitivities improve, the first detection is a matter of time.
Image credits: Riccardo Buscicchio, University of Birmingham
