Close Encounters Between Stellar Binaries And Supermassive Black Hole Binaries

Tidal disruption events(TDEs)can be used to study non-active supermassive black holes(SMBHs).After mergers between two galaxies,a supermassive black hole bina-ries(SMBHBs)will be formed inevitably at galactic centers(GCs).Thus,besides grav-itational waves,TDEs are also useful tools for the lurking SMBHBs at the GCs.On the other hand,there are lots of stellar binaries in galaxies,the interactions of stellar binaries with SMBHBs should be very frequent.And it is likely that the two component stars can be disrupted in turn by either SMBH(double TDEs;DTDEs).In this paper,we are going to study such kinds of interactions by scattering experiments.The research items in this thesis contain mainly two parts:the study of DTDEs with SMBHBs,and blue straggler stars,calcium-rich transients and eccentric stellar binaries with SMBHBs.First,we study encounters of stellar binaries with a SMBHB and focus on DTDEs.The encounters are studied by the N-body code REBOUND,and we assume that the orbits of stellar binaries are parabolic.According to our scattering experiments,we find that the time interval between two successive TDEs depends on the semi-major axis of stellar binaries when they encounter the first SMBH.For a representative stellar binary with one solar mass of each star and the semi-major axis less than 100 AU,the maximum time interval is?150 d when the stellar binary is disrupted by a single SMBH.However,in the case of SMBHB,the time interval is in the range from minutes to ten thousand years.DTDEs with the time interval larger than 150 d are called long time interval DTDEs(LDTDEs).The rate of DTDEs increases with the mass ratio of the SMBHB(qbhb),and tends to be constant when qbhb(?)0.1.The LDTDEs of the SMBHB may also be considered as two separate TDEs of the single SMBH,but this probability can be neglected,when the LDTDEs occur in 150 d-15 yr for the SMBHB with qbhb(?)0.1.As in gas poor galaxies,SMBHs are generally in quiescent state,we find the LDTDEs in 150 d-15 yr could be a useful tool to find SMBHB candidates with qbhhb(?)0.1 at galactic centers.Second,we continue to study the encounters of stellar binaries with the SMBHB,and focus on mergers and ejected stellar binaries.We find that the SMBHB can excite more stellar binaries to merge;and the fraction for the merger stars increases with the mass ratio qbhb when qbhb(?)0.1,and approaches to be a constant value for qbhb(?)0.01.After ejections by the SMBHB,the inner orbits of the stellar binaries are usually eccentric,and each encounter with the SMBHB can have an increase for the eccentricity.Moreover,we also find that the SMBHB with a larger mass ratio(e.g.,qbhb(?)0.01)can help to increase eccentricities of the ejected stellar binaries.Considering the fact that large eccentricities are helpful to increase the merger rate,and if stellar evolution is taken into account,our results suggest that some possible merger products(e.g.,calcium-rich transients and blue straggler stars(BSSs))and eccentric binaries(e.g.,binary X-ray sources and BSS binaries),which move away with large velocities and have large distances from GCs,could result from the interactions between stellar binaries and the SMBHB that has a high mass ratio qbhb(?)0.01.