LISA and the Existence of a Fast-Merging Double Neutron Star Formation Channel

TL;DR

This paper demonstrates that LISA will detect hundreds of Galactic double neutron star systems, including those from a fast-merging formation channel, providing unique insights into their orbital properties and formation scenarios.

Contribution

It introduces the potential of LISA to detect and characterize short-period, fast-merging DNSs, revealing a new observational window into their formation channels.

Findings

LISA can detect hundreds of Galactic DNSs within 4-8 years.

Detection is possible even at lower merger rates of 42 Myr$^{-1}$.

Orbital eccentricities as small as 10$^{-2}$ can be measured by LISA.

Abstract

Using a Milky Way double neutron star (DNS) merger rate of 210 Myr$^{-1}$, as derived by the Laser Interferometer Gravitational-Wave Observatory (LIGO), we demonstrate that the Laser Interferometer Space Antenna (LISA) will detect on average 240 (330) DNSs within the Milky Way for a 4-year (8-year) mission with a signal-to-noise ratio greater than 7. Even adopting a more pessimistic rate of 42 Myr$^{-1}$, as derived by the population of Galactic DNSs, we find a significant detection of 46 (65) Milky Way DNSs. These DNSs can be leveraged to constrain formation scenarios. In particular, traditional NS-discovery methods using radio telescopes are unable to detect DNSs with $P_{\rm orb}$ $\lesssim$1 hour (merger times $\lesssim$10 Myr). If a fast-merging channel exists that forms DNSs at these short orbital periods, LISA affords, perhaps, the only opportunity to observationally characterize these systems; we show that toy models for possible formation scenarios leave unique imprints on DNS orbital eccentricities, which may be measured by LISA for values as small as $\sim$10$^{-2}$.