| Compact objects are stellar remnants such as white dwarfs(WD),neutron stars(NS),and black holes(BH).They are products of stars at the end of their lives.The study of compact objects will help us to understand the laws of stellar evolution,the physics under extreme conditions,and ultimately,to understand better the relationship between the formation of elements,the evolution of galaxies and us as a human.Modern astronomy has moved into an era of multi-wavelength,multi-messenger,time-domain astronomy.The search for compact objects can invoke the observations from X-rays to the ultraviolet,optical band,infrared,all the way to radio frequencies that cover the full spectrum of electromagnetic waves.Detectors for gravitational waves,high energy neutrinos are also rapidly developing.The large-scale sky surveys provide a tremendous amount of observational data,which offer both opportunities and challenges for the search and the study of the compact objects.In this paper,I will explore some of the hot topics related to compact objects.This paper is organized as follows:Chapter 1 introduces the basic information of the three types of compact stars.Then we introduce two astrophysical processes that are related to compact objects:the merger of compact binary stars and the hyper-accretion of black holes.Three associated high-energy astrophysical phenomena are introduced:the gravitational wave radiations,gamma-ray bursts,and the kilonovae.Then I will briefly introduce the searching methods of compact objects.Chapters 2 and 3 will introduce the association between BH hyper-accretion the kilonova,and the gamma-ray bursts that are caused by BH-NS or NS-NS mergers.We propose two possible mechanisms as the injection of energy and materials from the BH hyper-accretion disk to the kilonova:the vertical advection effect and the baryonic outflows mechanism.Our models consider the energy balance of the accretion disk and can well explain the radiation energy injection of the observed kilonova events.Chapters 4 and 5 describe some of our attempts in the searching for compact objects.We studied the stellar evolution models,the formation channels of stellar-mass BHs,and the detection limit of the LAMOST telescope,to estimate the number and distributions of the stellar BH that may be found by LAMOST during its sky surveys.In Chapter 5,I present a single-line spectroscopic binary system that contains a compact object.The properties of the system are analyzed from the photometry and spectroscopy,and the identity of the invisible compact object is speculated.In Chapter 6,I will discuss an application of compact binary systems.We use the periodic accretion of an NS-WD system in an orbit with large eccentricity to explain the periodic activities of repeating fast radio bursts.The origin of the fast radio burst is briefly discussed.In the last Chapter,a succinct plan for future research will be layout as to conclude this thesis. |
