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. 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] open new doors in astronomy.

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.

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 (pictured above, credits: LVK) instead of a black hole, it would enable new studies across fundamental physics, astrophysics and cosmology.

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.

Professor Hannuksela’s team includes PhD students in CUHK’s Department of Physics Laura Uronen, Hemantakumar Phurailatpam and Jason Poon Sheung-chi.

[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.