The visibility of double neutron star binaries to LISA

Sammanfattning: Double neutron star binaries (DNSBs) in the mHz gravitational wave (GW) regime are an important group of objects which the GW detector LISA will be able to observe. The detection and parametrization of these objects will help develop our current understanding of neutron star formation and evolution. In this thesis, we synthesize a group of DNSBs using data from Church et al. (2011) and normalize the population to observed data of DNSB merger rates (Belczynski et al. 2018; Pol et al. 2019). The DNSB’s orbits are evolved in order to determine if their GW’s frequency is within the LISA band at present time. The binaries that are not within the LISA band are subsequently removed. Initial positions are then assigned to the DNSBs using a model for the stellar density in the galactic thin disk (McMillan, 2017), as well as initial birth times on the assumption that the star formation rate is constant to present time and begins at −10 Gyr from present day. We integrate their local and galactic orbits using a simple galactic potential (Repetto et al., 2012), as well as the separation evolution of a binary orbit (Peters, 1964), until present time. We calculate the strain of the DNSB’s GWs (Kupfer et al., 2018) and convert to both power spectral density and characteristic strain (Moore et al., 2014). The LISA sensitivity curve (Amaro-Seoane et al., 2017), including the background contribution of galactic binaries (GBs), is then compared to the characteristic strain of the DNSB population which shows that 265 DNSBs will be visible (SNR> 1) to LISA after a nominal mission time of 4 years. We show that 42 of these systems will also be resolvable (SNR> 5) to LISA. If the mission is extended to 10 years, the number of resolvable systems goes up to 79. We also show that these resolvable DNSB systems will be mostly clustered around the Galactic Center (GC) and our solar system, with the furthest DNSBs not exceeding 20 kpc from LISA.