High-energy and time-domain astrophysics is a cutting-edge field in astronomy that studies the most violent and dynamic processes in the universe. It focuses on the immense energy released by compact objects such as black holes and neutron stars during accretion, merger, and outburst events, and their evolution over time. The Zhejiang University Institute of Astronomy has identified this as one of its four foundational research pillars. We have assembled an interdisciplinary team of researchers, including Professor Cao Xinwu, Researcher Liu Bin, Researcher Chen Ping, and Researcher Jiao Jinlong, dedicated to uncovering the physical laws behind these extreme cosmic phenomena from multiple perspectives encompassing theory, simulation, and multi-wavelength observation.
1. Main Research Directions
Our research is closely centered on the extreme physical processes involving compact objects, primarily covering the following core areas:
1.1 Active Galactic Nuclei and Supermassive Black Hole Physics
This direction focuses on the accretion, radiation, and interaction with the surrounding environment of supermassive black holes at the centers of galaxies.
Central Engine and Changing-Look Mechanisms: Investigating the structure and radiative properties of the accretion disk and corona around the central black hole in Active Galactic Nuclei (AGN), particularly the physical causes behind dramatic short-term changes in their spectra and luminosity (known as changing-look phenomena).
Tidal Disruption Events: Studying the complete physical picture of stars being torn apart by the tidal forces of a central supermassive black hole, leading to a transient accretion process. This includes matter fallback, accretion flow formation, jet production, and their multi-wavelength radiative signatures.
Black Hole Accretion and Feedback: Gaining a deeper understanding of how accretion processes power AGN and how the resulting radiation and outflows influence the evolution of their host galaxies.
1.2 Compact Object Mergers and Gravitational-Wave Astrophysics
This direction concerns the dynamical evolution of stellar-mass black holes, neutron stars, and other compact objects, and the gravitational waves and electromagnetic counterparts produced by their mergers.
Dynamical Processes in Nuclear Star Clusters: Researching the formation, dynamical evolution (e.g., mergers induced by the von Zeipel–Lidov–Kozai, ZLK, mechanism), and final merger rates of stellar-mass binary black holes, binary neutron stars, and similar systems in the extreme environments of galactic nuclear star clusters coexisting with supermassive black holes.
Multi-messenger Studies of Gravitational Wave Sources: Theoretically predicting the multi-messenger signals (gravitational waves, short gamma-ray bursts, kilonovae, etc.) from merger events and exploring the scientific value of their joint observation for constraining the equation of state of compact objects, cosmological parameters, and more.
Formation of Special Gravitational-Wave Events: Investigating how dynamical processes (e.g., hierarchical mergers) can produce gravitational-wave events with special parameters, such as those located in the mass gap (e.g., GW231123).
1.3 Supernova Physics and Time-domain Astronomy
Led by Researcher Chen Ping, this direction focuses on the ultimate explosions in stellar evolution and the transient phenomena they trigger, representing one of the most scientifically driven frontiers in modern time-domain astronomy.
Supernova Progenitors and Explosion Mechanisms: Studying the progenitor systems of different supernova types (e.g., Type Ia, core-collapse), their triggering mechanisms (thermonuclear explosion or core collapse), and the associated neutrino and gravitational wave production during the explosion.
Explosion Dynamics and Radiative Transfer: Using numerical simulations to research the propagation of shock waves in supernova explosions, nucleosynthesis processes, and the expansion, radiative cooling, and spectral evolution of the ejecta post-explosion.
Transient Source Searches and Multi-messenger Observations: Systematically searching for and monitoring various transients like supernovae, fast radio bursts, and tidal disruption events using large time-domain surveys. This involves comprehensive analysis combining multi-wavelength (optical, X-ray, radio) and even multi-messenger (neutrinos, gravitational waves) data to reveal their physical nature.
2. Research Methods and Distinctive Features
The team employs a deeply integrated research paradigm combining multi-messenger observations, theoretical modeling, and high-performance numerical simulations.
Theory: Developing a series of theoretical models ranging from general relativistic dynamics and accretion disk theory to supernova explosion physics and radiative transfer.
Simulation: Widely applying and developing N-body simulations, fluid/magnetohydrodynamic (MHD) simulations, radiative transfer calculations, and multi-dimensional supernova explosion simulations. Leveraging the institute's Galaxy high-performance heterogeneous computing platform, we achieve high-fidelity numerical reconstructions of extreme physical processes.
Observation: Deeply participating in domestic and international large-scale time-domain surveys (e.g., LAST, CSST) and space-based X-ray and gamma-ray telescope projects (e.g., SVOM). We systematically search for, identify, and intensively study various transient sources and high-energy astrophysical objects.
3. Scientific Goals and Significance
Through the aforementioned research, we aim to:
Deeply understand the growth of supermassive black holes and their feedback effects on galaxy evolution.
Elucidate the formation channels and physical laws governing binary compact object mergersand massive stellar explosions, which act as cosmic heavy-element factories and sources of gravitational waves.
Reveal the physical origins of various violent transient phenomena in the universe, advancing the field of time-domain astronomy.
Cultivate top-tier interdisciplinary talent skilled in handling cutting-edge theory, massive datasets, and complex simulations, providing intellectual support for national strategic development in areas like space exploration and high-performance computing.
High-energy and time-domain astrophysics connects the smallest compact objects in the universe with the largest-scale galaxy evolution, standing as one of the most active frontiers in contemporary astrophysics. The team in this direction at the Zhejiang University Institute of Astronomy is committed to achieving breakthrough discoveries in this field. We look forward to collaborating with peers both in China and abroad to jointly unravel the mysteries of the universe's most extreme phenomena.
