Determining the Nature of White Dwarfs from Low-frequency Gravitational Waves

Wen-Biao Han,Xi-Long Fan

doi:10.3847/1538-4357/aab03c

Abstract

Abstract An extreme-mass-ratio system composed of a white dwarf (WD) and a massive black hole can be observed by low-frequency gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA). When the mass of the black hole is around 104 ∼ 105 M ⊙, the WD will be disrupted by the tidal interaction at the final inspiraling stage. The event position and time of the tidal disruption of the WD can be accurately determined by the gravitational wave signals. Such position and time depend upon the mass of the black hole and especially on the density of the WD. We present the theory that by using LISA-like gravitational wave detectors, the mass–radius relation and the equations of state of WDs could be strictly constrained (accuracy up to 0.1%). We also point out that LISA can accurately predict the disruption time of a WD and forecast the electromagnetic follow-up of this tidal disruption event.

Highlights

The era of gravitational wave (GW) astronomy arrived when the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) observed the first gravitational wave event GW150914 (Abbott et al 2016)
An extreme-mass-ratio system composed of a white dwarf (WD) and a massive black hole can be observed by the lowfrequency gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA)
We present the theory by using LISA-like gravitational wave detectors, the mass-radius relation and the equations of state of WDs could be strictly constrained

Summary

INTRODUCTION

The era of gravitational wave (GW) astronomy arrived when the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) observed the first gravitational wave event GW150914 (Abbott et al 2016). Since GW interferometers (like LISA) are very sensitive to the phase of the signal, this phase difference is crucial for distinguishing the disruption position and time of the WD Such position and time are determined by the mass and radius of WD and the mass of the black hole. With such kind of WD disruption events, LISA will constrain the mass-radius relation of WDs much better than current astronomical methods (Magano et al 2017; Holberg et al 2012; Tremblay et al 2012). By using the TDE, in principle, one can independently obtain the tidal radius of WDs from the GW’s cutoff frequency. From the radius-mass relation (7) and Eq (1), we can determine the tidal radius and calculate the remaining time of TDE to ISCO. The difference of two remaining times is just the expected time of TDE relative to the position at radius r

WD’S EOS CONSTRAINT RESULTS

Findings

DISCUSSION