Astronomy and Astrophysics Group

Very Large Array Radio Telescope

People

Research Activities

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

Dr. 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.

Dr. 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.

Dr. 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, Dr. Lim uses primarily radio telescopes (e.g., VLA, SMA, ALMA) and optical-infrared telescopes (e.g., CFHT, HST). Dr. 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, Dr. Lim has built a strong group of undergraduate and graduate students working on gravitational lensing at HKU. Dr. Lim actively recruits talented undergraduate students for casual research in preparation for their capstone and graduate studies.

Dr. 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.

Dr. 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/.

Some Representative Publications

Dr. J.L.X. Dai

1. “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)
2. “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)
3. “An asymmetric electron-scattering photosphere around optical tidal disruption events,” Leloudas, G., Bulla, M., Cikota, A., Dai, L., Thomsen, L. L., et al., Nature Astronomy, 6, 1193 (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. “X-Ray Fluorescence from Super-Eddington Accreting Black Holes,” Thomsen L. L., Dai, J. L., Ramirez-Ruiz, E., Kara, E., & Reynolds, C., The Astrophysical Journal Letters, 884, L21 (2019)
6. “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)
    

Dr. J.J.L. Lim

1. "A likely Supermassive Black Hole revealed by its Einstein radius in Hubble Frontier Field Image," Chen, M. C., Broadhurst, T., Lim, J., Diego, J. M., Ohyama, Y., Ford, H., & Benítez, N, The Astrophysical Journal, 863, 135 (2018)
2. "Magnification Bias of distant Galaxies in the Hubble Frontier Fields: Testing Wave vs. Particle Dark Matter predictions," Leung, E., Broadhurst, T., Lim, J., Diego, J. M., Chiueh, T., Schive, H.-Y., & Windhorst, R., The Astrophysical Journal, 862, 156 (2018)
3. "Geometric Corroboration of the Earliest Lensed Galaxy at z ≃ 10.8 from Robust Free-form Modelling," Chan, B. Y. M., Broadhurst, T., Lim, J., Diego, J. M., Zitrin, A., Coe, D., & Ford, H., The Astrophysical Journal, 835, 44 (2017)
4. "The Role of Electron Excitation and Nature of Molecular Gas in Cluster Central Elliptical Galaxies," Lim, J., Dinh-V-T., Vrtilek, J., David, L. P., & Forman, W., The Astrophysical Journal, 850, 31 (2017)
5. “The High-Velocity System: Infall of a Giant Low-Surface-Brightness Galaxy towards the center of the Perseus Cluster”, A. Yu, J. Lim, Y. Ohyama, J. C. C. Chan, & T. Broadhurst, The Astrophysical Journal, 814, 101 (2015)
6. “A Rigorous Free-form Lens Model of A2744 to Meet the Hubble Frontier Fields Challenge”, D. Lam, T. Broadhurst, J.M. Diego, J.J.L. Lim, D. Coe, H.C. Ford and Z. Wei, The Astrophysical Journal, 697, 98 (2014)
7. “Molecular Gas in the X-Ray Bright Group NGC 5044 as Revealed by ALMA”, L.P. David, J.J.L. Lim, et al., The Astrophysical Journal, 792, 94 (2014)
8. "A Molecular Hydrogen Nebula in the Central cD Galaxy of the Perseus Cluster", J.J.L. Lim, Y. Ohyama, C.H. Yan, D.V. Trung and S.Y. Wang, The Astrophysical Journal, 744, 112 (2012)
    

Dr. S.C.Y. Ng

1. "A systematic study of soft X-ray pulse profiles of magnetars in quiescence”, Chin-Ping Hu, C.-Y. Ng and Wynn C. G. Ho, Monthly Notices of the Royal Astronomical Society, 485 (2019)
2. "The Reacceleration of the Shock Wave in the Radio Remnant of SN 1987A”, Y. Cendes , B. M. Gaensler, C.-Y. Ng , G. Zanardo, L. Staveley-Smith, and A. K. Tzioumis, the Astrophysical Journal, 867, 65 (2018)
3. "Chandra Phase-Resolved Spectroscopy of the High-Magnetic-Field Pulsar B1509-58", Chin-Ping Hu, C.-Y. Ng, J. Takata, R. M. Shannon, and S. Johnston, the Astrophysical Journal, 838, 156 (2017)
4. “Discovery of a Synchrotron Bubble Associated with PSR J1015-5719”, C.-Y. Ng, R. Bandiera, R. W. Hunstead, and S. Johnston, the Astrophysical Journal, 842, 100 (2017)
5. "Radio Polarization Observations of the Snail: A Crushed Pulsar Wind Nebula in G327.1-1.1 with a Highly Ordered Magnetic Field",Y. K. Ma, C.-Y. Ng, N. Bucciantini, P. O. Slane, B. M. Gaensler, & T. Temim, The Astrophysical Journal, 820, 100 (2016)
6. "An anti-glitch in a magnetar", R.F. Archibald , S.C.Y. Ng, K.N. Gourgouliatos, D. Tsang, P. Scholz, A.P. Beardmore, N. Gehrels, J.A. Kennea, Nature, 497, 591 (2013)

Dr. J.C.S. Pun

1. "Measurement of the Electron Antielectron Oscillation with 1958 Days of Operation at Daya Bay", F. P. An, et al. (Daya Bay Reactor Neutrino Experiment collaboration), Physical Review Letters, 121, 241805 (2018)
2. "Measurement of cosmic-ray muons and muon-induced neutrons in the Aberdeen Tunnel Underground Laboratory" S. Blyth, et al. (Aberdeen Tunnel Underground Experiment collaboration), Physical Review D, 93, 072005 (2016)
3. "The destruction of the circumstellar ring of SN1987A," C. Fransson, J. Larsson,... C.S.J. Pun, G. Sonneborn and B. Sugerman, The Astrophysical Journal Letters, 806, L19 (2015)
4. "Contributions of artificial lighting sources on light pollution in Hong Kong measured through a night sky brightness monitoring network", C.S.J. Pun, C.W. So, W.Y. Leung and C.F. Wong, Journal of Quantitative Spectroscopy & Radiative Transfer, 139, 90-108 (2014)
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)