Physical and radiation properties of compact objects

As the final product of stellar evolution, compact objects serve as cosmic laboratories for exploring extremely strong gravitational, high-density, and strong magnetic field environments. However, due to the limitations of observation methods and the unique properties of compact objects, only a very small part has been discovered to date, thus their physical properties and evolution remain a mystery. The observation and study of compact objects often require their interaction with other celestial bodies. Therefore, based on recent research results from Wuhan University, this review summarizes the related research on neutron stars and black holes through three aspects: X-ray binaries, globular clusters, and supermassive black holes. This review first introduces the accretion features of black holes and neutron stars in binary systems. Due to the strong magnetic field in neutron stars, the accretion features and radiation environment of a neutron star binary system are more complex compared to those of a black hole binary system. The center energy of the cyclotron absorption line is a key factor in determining the strength of the magnetic field of a source. Thus, thanks to the wide energy range and unique advantages of the Insight-HXMT satellite, this review focuses on the study of cyclotron absorption lines to limit the magnetic field and accretion model of the neutron star. Additionally, this review introduces the first application of wavelet analysis in the field of binary systems. The more accurate time-frequency domain information obtained by this method can provide much more detailed information of the quasi-periodic oscillation signals, offering features that cannot be obtained by traditional power density spectra and contributing to a deeper understanding of the mechanism of quasi-periodic oscillations. Furthermore, there is an inseparable relationship between compact objects and globular clusters. The compact cluster environment provides an excellent location for black holes to capture other celestial bodies and form X-ray binary systems, gravitational wave sources, and even intermediate-mass black holes. On the other hand, the dynamic process of black holes can change the dynamic structure and evolutionary process of host clusters, as well as the evolution, distribution, and abundance of visible binary systems in the clusters. This, in turn, provides many observational possibilities for studying the dynamic evolution process of black holes in globular clusters. Finally, supermassive black holes are generally located in the center of large galaxies, such as Sagittarius A* at the center of the Milky Way, and have unique physical properties and observational features, such as the evolution of active galactic nuclei, tidal disruption events, and bubble structures near the galactic center. Unlike the much longer evolution timescales of active galactic nuclei, the physical processes involved in tidal disruption events, such as the formation of accretion disks, the state transition from high to low accretion rates, and the generation of outflows, are condensed within just a few months to a few years. This provides an important sample for relevant research. Moreover, bubbles near the galactic center are often considered to be related to the activity history of the galactic center. By displaying research results on tidal disruption events and bubbles near the galactic center, this review analyzes the properties and features of supermassive black holes, providing insights into their accretion processes, activity mechanisms, and surrounding cloud environments.