Stars stripped in binaries -- the living gravitational wave sources

TL;DR

This paper predicts the population and observable signatures of binary systems with stripped stars and compact objects, highlighting their potential as multi-messenger sources for gravitational wave and electromagnetic observations with LISA.

Contribution

The authors develop a Monte Carlo simulation to estimate the Galactic population of stripped star binaries with compact objects, providing predictions for their detectability and observational signatures.

Findings

Predicts 0-100 white dwarf companions and up to 4 neutron star companions detectable by LISA.

Over 90% of these binaries show large radial velocity shifts, detectable spectroscopically.

Stripped star + neutron star binaries are expected to be X-ray bright.

Abstract

Binary interaction can cause stellar envelopes to be stripped, which significantly reduces the radius of the star. The orbit of a binary composed of a stripped star and a compact object can therefore be so tight that the gravitational radiation the system produces reaches frequencies accessible to the Laser Interferometer Space Antenna (LISA). Two such stripped stars in tight orbits with white dwarfs are known so far (ZTF J2130+4420 and CD-30 11223), but many more are expected to exist. These binaries provide important constraints for binary evolution models and may be used as LISA verification sources. We develop a Monte Carlo code that uses detailed evolutionary models to simulate the Galactic population of stripped stars in tight orbits with either neutron star or white dwarf companions. We predict 0-100 stripped star + white dwarf binaries and 0-4 stripped star + neutron star binaries with SNR>5 after 10 years of observations with LISA. More than 90% of these binaries are expected to show large radial velocity shifts of $\gtrsim 200$ km/s, which are spectroscopically detectable. Photometric variability due to tidal deformation of the stripped star is also expected and has been observed in ZTF J2130+4420 and CD-30 11223. In addition, the stripped star + neutron star binaries are expected to be X-ray bright with $L_X \gtrsim 10^{33} - 10^{36}$ erg/s. Our results show that stripped star binaries are promising multi-messenger sources for the upcoming electromagnetic and gravitational wave facilities.