Research

The group's researches mainly focus on high-energy astrophysics, late stage stellar evolution, observational cosmology and planetary science (including the solar system).

Prof. Dai is a theoretical and computational astrophysicist, working to understand relativistic phenomena around black holes. She mainly develops and employs novel numerical simulations to model these energetic phenomena and connect theory to observations. She is also involved in several observational collaboration teams. Her current research interests mainly include: (1) black hole accretion and outflows, (2) tidal disruption events and other black hole transient phenomena, (3) X-ray reflection and reverberation, and (4) multi-messenger astrophysics.

Prof. Lee is a planetary dynamicist who works on the formation and dynamical evolution of planetary bodies (planets, moons, etc.) in our Solar System and in planetary systems around other stars. He is also an expert in numerical methods for dynamical simulations of planetary systems. His current research interests include the dynamics and origins of (1) orbital resonances in extrasolar planetary systems, (2) planets in binary star systems, (3) the orbital architecture of the planets in our Solar System, and (4) the satellite systems of Jupiter, Uranus and Pluto-Charon.

Prof. Lim's research has spanned a broad range of topics, including (i) stellar coronal magnetic activity, (ii) the formation and late evolution of stars in our Galaxy, (iii) star formation and AGNs in nearby galaxies, (iv) X-ray cooling flows in galaxy clusters, and (v) astrophysical applications of gravitational lensing, including weighing supermassive black holes, evolution of galaxies in the early Universe, as well as the nature of dark matter. The present focus of his work is on topics (iii)-(v). As an observational astronomer, Prof. Lim uses primarily radio telescopes (e.g., VLA, SMA, ALMA) and optical-infrared telescopes (e.g., CFHT, HST). Prof. Lim has mentored many graduate students, a number of whom have gone on to PhD programs in the USA and Europe, or have since become postdoctoral fellows. He collaborates with many astronomers worldwide, bringing international exposure to his students. Over the past 6 years, in collaboration with Prof. Thomas Broadhurst at Ikerbasque, Spain, Prof. Lim has built a strong group of undergraduate and graduate students working on gravitational lensing at HKU. Prof. Lim actively recruits talented undergraduate students for casual research in preparation for their capstone and graduate studies.

Prof. Ng studies extreme objects in our Galaxy, including magnetars, energetic pulsars, pulsar wind nebulae (PWNe), and supernova remnants. He has led observational projects using world-class telescopes in X-rays and radio, such as the Chandra X-ray Observatory, XMM-Newton, the Expanded Very Large Array, and the Australia Telescope Compact Array. He has identified a pulsar moving at an enormous velocity over 2,000 km/s. He has also developed a powerful 3D modeling technique to capture the X-ray torus and jet morphology of PWNe and to measure the structure and evolution of the supernova remnant 1987A.

Prof. Ng's latest research focuses on the magnetic fields of neutron stars and their environments. Employing X-ray observations, he measures the surface temperature of magnetars, which are stars with the strongest magnetic fields in the Universe, to understand their extreme properties and their connection with ordinary radio pulsars. In addition, he maps the magnetic field configurations of PWNe using radio telescopes, in order to probe the cosmic ray production and transport in these systems. Further information can be found at the webpage http://www.physics.hku.hk/~ncy/.

Prof. Wang is a theoretical and computational astrophysicist working on the dynamics of dense stellar environments and the transients they produce. His research focuses on the accretion disks of active galactic nuclei (AGN) and galactic nuclei, where stars and compact objects can be captured, tidally disrupted, paired into binaries, and driven to merge. A central goal is to understand how AGN disks reshape nuclear star clusters through repeated gas drag on disk-crossing stars and compact objects, and how this disk-cluster coupling affects tidal disruption events, changing-look AGN, and gravitational-wave sources. More broadly, his work uses nuclear transients and compact-object mergers as probes of the hidden stellar and black-hole populations around massive black holes.

Prof. Wang also develops open-source computational tools for astrophysical dynamics and transient modeling. These include SpaceHub, a high-precision gravity integration toolkit for close encounters, extreme orbits, and few-body mergers, and VegasAfterglow, a fast framework for modeling gamma-ray burst afterglows directly against multi-wavelength observations. As a member of the Einstein Probe, SVOM, and LHAASO collaborations, he works closely with observational teams studying fast high-energy transients, including gamma-ray bursts and fast X-ray transients, across the electromagnetic spectrum from X-rays to TeV gamma-rays. Students working with Prof. Wang will be trained in theoretical modeling, numerical simulation, Bayesian inference, and modern software-development workflows.

Prof. Zhang is a theoretical astrophysicist actively collaborating with observers. His research covers a wide range of topics in the area of high-energy, multi-messenger astrophysics. Research topics include black holes of all sizes, neutron stars of different species, relativistic jets launched from these systems and their interactions with the ambient medium, the physics of astrophysical transients, and applying them as cosmic probes to study cosmology and constrain fundamental physics. The research is multi-wavelength (data from the entire electromagnetic spectrum from radio all the way to TeV gamma-rays) and multi-messenger (including gravitational waves, neutrinos, and cosmic rays, besides the traditional electromagnetic radiation) in nature. The three areas that take up most of Prof. Zhang’s time include gamma-ray bursts (GRBs) and their softer siblings known as fast X-ray transients (FXTs), fast radio bursts (FRBs), as well as electromagnetic/neutrino counterparts of gravitational wave events. Prof. Zhang’s research has three modes: in the solo mode, he writes single-author books, reviews, and research papers; in the small-collaboration mode, he works with his students/postdocs to carry out cutting-edge theoretical, computational, and observational research projects in many frontier areas listed above; and in the large-collaboration mode, he plays a leading role in several large-collaboration teams to carry out discoveries and observations of new phenomena and provide timely theoretical guidance to these teams. Currently, he is one of the leaders of the FAST (Five-hundred-meter Aperture Spherical Telescope) FRB Key Science Project (served as PI of the Project from 2020-2025), Chair of the multi-messenger science topical panel and member of science management committee of the Einstein Probe mission, and Mission Scientist of the Chinese-French GRB mission SVOM (Space Variable Objects Monitor).

(For the complete publication list of the department, please go back to Research.)

Prof. J.L.X. Dai

1. “Detecting Population III Stars through Tidal Disruption Events in the Era of JWST and Roman”, Kar Chowdhury R., Chang J.N.Y., Dai L., Natarajan P., The Astrophysical Journal Letters, 966, L33 (2024)
2. “The Effects of Gas Angular Momentum on the Formation of Magnetically Arrested Disks and the Launching of Powerful Jets,” Kwan, T. M., Dai, L., & Tchekhovskoy, A., The Astrophysical Journal Letters, 946, L42 (2023)
3. “Dynamical Unification of Tidal Disruption Events,” Thomsen, L. L., Kwan, T. M., Dai, L., Wu, S.~C., Roth N., & Ramirez-Ruiz E., The Astrophysical Journal Letters, 937, L28 (2022)
4. “The Physics of Accretion Discs, Winds and Jets in Tidal Disruption Events,” Dai, L., Lodato, G., & Cheng, R., Space Science Reviews, 217, 12 (2021)
5. “A Unified Model for Tidal Disruption Events,” Dai, L., McKinney, J., Roth, N., Ramierz-Ruiz, E. & Miller, M. C., The Astrophysical Journal Letters, 859, 2 (2018)
   
   

Prof. J.J.L. Lim

1. “Dark Matter Distinguished by Skewed Microlensing in the "Dragon Arc"”, Tom Broadhurst, Sung Kei Li, Amruth Alfred, Jose M. Diego, Paloma Morilla, Patrick L. Kelly, Fengwu Sun, Masamune Oguri, Hayley Williams, Rogier Windhorst, Adi Zitrin, Katsuya T. Abe, Wenlei Chen, Liang Dai, Yoshinobu Fudamoto, Hiroki Kawai, Jeremy Lim, Tao Liu, Ashish K. Meena, Jose M. Palencia, George F. Smoot, and Liliya L.R. Williams, The Astrophysical Journal Letters, 978, L5 (2025)
2. “Star Formation, Nebulae, and Active Galactic Nuclei in CLASH Brightest Cluster Galaxies. I. Dependence on Core Entropy of Intracluster Medium”, Arsen Levitskiy, Jeremy Lim, Youichi Ohyama, Juno Li, and Megan Donahue, The Astrophysical Journal, 971, 42 (2024)
3. “A Lens Finder Map to Check Claimed High-z Galaxies behind SMACS J0723.3-7327”, Alex Chow, Sung Kei Li, Jeremy Lim, Tom Broadhurst, Man Cheung Alex Li, James Nianias, Jake Summers, and Rogier Windhorst, The Astrophysical Journal, 962, 30 (2024)
4. “Einstein rings modulated by wavelike dark matter from anomalies in gravitationally lensed images”, Alfred Amruth, Tom Broadhurst, Jeremy Lim, Masamune Oguri, George F. Smoot, Jose M. Diego, Enoch Leung, Razieh Emami, Juno Li, Tzihong Chiueh, Hsi-Yu Schive, Michael C. H. Yeung & Sung Kei Li, Nature Astronomy, 7, 736-747 (2023)
5. “Sustained formation of progenitor globular clusters in a giant elliptical galaxy”, Broadhurst, T., Lim, J., Medezinski, E., Ohyama, Y., Wong, W., Nature Astronomy, 4, 153 (2020) 
   
   

Prof. S.C.Y. Ng

1. “Radio Study of the Pulsar Wind Nebula Powered by PSR B1706-44”, Liu, Y. H., Ng, C. -Y., Dodson R., The Astrophysical Journal, Volume 945, Issue 1, id.82, 11 pp. (2023)
2. “High-resolution Radio Study of the Dragonfly Pulsar Wind Nebula Powered by PSR J2021+3651”, Jin, Ruolan, Ng, C.-Y., Roberts, Mallory S. E., Li, Kwan-Lok, The Astrophysical Journal, Volume 942, Issue 2, id.100, 9 pp. (2023)
3. “Magnetic Field Structure and Faraday Rotation of the Plerionic Supernova Remnant G21.5-0.9”, Lai, Paul C. W., Ng, C. -Y., Bucciantini, Niccolo', The Astrophysical Journal, Volume 930, Issue 1, id.1, 10 pp. (2022)
4. “A Comprehensive Study of the Spectral Variation and the Brightness Profile of Young Pulsar Wind Nebulae”, Hu, Chin-Ping, Ishizaki, Wataru, Ng, C. -Y., Tanaka, Shuta J., Mong, Y. –L, The Astrophysical Journal, Volume 927, Issue 1, id.87, 11 pp. (2022)
5. “High-frequency radio observations of two magnetars, PSR J1622 - 4950 and 1E 1547.0 - 5408”, Chu, Che-Yen, Ng, C. -Y., Kong, Albert K. H., Chang, Hsiang-Kuang, Monthly Notices of the Royal Astronomical Society, Volume 503, Issue 1, pp.1214-1220 (2021)

Dr. J.C.S. Pun

1. “Natural experiments from Earth Hour reveal urban night sky being drastically lit up by few decorative buildings,” Chu Wing So, Chun Shing Jason Pun, Shengjie Liu, Sze Leung Cheung, Ho Keung Kenneith Hui, Kelly Blumenthal, Constance Elaine Walker, Scientific Reports, 15, 21414 (2025)
2. “Analyzing the sources and variations of nighttime lights in Hong Kong from VIIRS monthly data,” Shengjie Liu, Chu Wing So, Chun Shing Jason Pun, Remote Sensing, 17, 1447 (2025)
3. “Comprehensive Measurement of the Reactor Antineutrino Spectrum and Flux at Daya Bay,” F. P. An, ……C. S. J. Pun et al. (Daya Bay Collaboration), Physical Review Letters, 134, 201802 (2025)
4. “Measurement of cosmic-ray muons and muon-induced neutrons in the Aberdeen Tunnel Underground Laboratory”, S. Blyth,……C.S.J. Pun et al. (Aberdeen Tunnel Underground Experiment collaboration), Physical Review D, 93, 072005 (2016)
5. "The discovery of an X-ray / UV stellar flare from the late-K/early-M dwarf LMC 335," B.T.H. Tsang, C.S.J. Pun,R. DiStefano, K.L. Li and A.K.H. Kong, The Astrophysical Journal, 754, 107 (2012)

Prof. Y.H. Wang

1. "VegasAfterglow: A high-performance framework for gamma-ray burst afterglows", Yihan Wang, Connery Chen and Bing Zhang, Journal of High Energy Astrophysics, 50, 100490 (2026)
2. "Evidence of a past merger of the Galactic Centre black hole", Yihan Wang and Bing Zhang, Nature Astronomy, 8, 1592-1601 (2024)
3. "Free-floating binary planets from ejections during close stellar encounters", Yihan Wang, Rosalba Perna and Zhaohuan Zhu, Nature Astronomy, 8, 756-764 (2024)
4. "Stellar/BH population in AGN discs: direct binary formation from capture objects in nuclei clusters", Yihan Wang, Zhaohuan Zhu and Douglas N. C. Lin, Monthly Notices of the Royal Astronomical Society, 528, 4958-4975 (2024)
5. "SpaceHub: A high-performance gravity integration toolkit for few-body problems in astrophysics", Yi-Han Wang, Nathan W. C. Leigh, Bin Liu and Rosalba Perna, Monthly Notices of the Royal Astronomical Society, 505, 1053-1070 (2021)

Prof. B. Zhang

1. “The physics of fast radio bursts”, Bing Zhang, Reviews of Modern Physics, 95(3), 035005 (2023)
2. “The physical mechanisms of fast radio bursts”, Bing Zhang, Nature, 587, 45-53 (2020)
3. “The physics of gamma-ray bursts”, Bing Zhang, Cambridge University Press, DOI: 10.1017/9781107027619 (a 578-page textbook/monograph), (2018)
4. “The internal-collision-induced magnetic reconnection and turbulence (ICMART) model of gamma-ray bursts”, Bing Zhang & Huirong Yan, The Astrophysical Journal, 726(2), 90 (2011)
5. “Physical processes shaping GRB X-ray afterglow lightcurves: theoretical implications from the Swift XRT observations”, Bing Zhang, Yi-Zhong Fan, Jaroslaw Dyks, Shiho Kobayashi, Peter Mészáros, David N. Burrows, John A. Nousek & Neil Gehrels, The Astrophysical Journal, 642(1), 354-370 (2006)