Constraining the P-Mode-G-Mode Tidal Instability with GW170817

B. P. Abbott, California Institute of Technology
R. Abbott, Louisiana State University
T. D. Abbott, University of Salerno
F. Acernese, Complesso Universitario di Monte sant'Angelo
K. Ackley, Monash University
C. Adams, Universite Grenoble Alpes
T. Adams, University of Sannio
P. Addesso, Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
R. X. Adhikari, Leibniz University Hannover
V. B. Adya, University of Illinois at Urbana-Champaign
C. Affeldt, University of Cambridge
B. Agarwal, National Institute for Subatomic Physics
M. Agathos, Massachusetts Institute of Technology
K. Agatsuma, National Institute for Space Research
N. Aggarwal, Gran Sasso Science Institute
O. D. Aguiar, National Institute for Nuclear Physics
L. Aiello, Inter-University Centre for Astronomy and Astrophysics India
A. Ain, Tata Institute of Fundamental Research
P. Ajith, University of Wisconsin-Milwaukee
B. Allen, University of Pisa
G. Allen, Sezione di Pisa
A. Allocca, University of Valencia
M. A. Aloy, Australian National University
P. A. Altin, Institut National de Physique Nucleaire et de Physique des Particules
A. Amato, University of Strathclyde
A. Ananyeva, ComUE Paris-Saclay
S. B. Anderson, California State University Fullerton
W. G. Anderson, Universite Paris 7
S. V. Angelova, European Gravitational Observatory
S. Antier, Chennai Mathematical Institute
Marc Favata, Montclair State University

Abstract

We analyze the impact of a proposed tidal instability coupling p modes and g modes within neutron stars on GW170817. This nonresonant instability transfers energy from the orbit of the binary to internal modes of the stars, accelerating the gravitational-wave driven inspiral. We model the impact of this instability on the phasing of the gravitational wave signal using three parameters per star: An overall amplitude, a saturation frequency, and a spectral index. Incorporating these additional parameters, we compute the Bayes factor (lnB!pgpg) comparing our p-g model to a standard one. We find that the observed signal is consistent with waveform models that neglect p-g effects, with lnB!pgpg=0.03-0.58+0.70 (maximum a posteriori and 90% credible region). By injecting simulated signals that do not include p-g effects and recovering them with the p-g model, we show that there is a ≃50% probability of obtaining similar lnB!pgpg even when p-g effects are absent. We find that the p-g amplitude for 1.4 MâŠneutron stars is constrained to less than a few tenths of the theoretical maximum, with maxima a posteriori near one-Tenth this maximum and p-g saturation frequency ∼70 Hz. This suggests that there are less than a few hundred excited modes, assuming they all saturate by wave breaking. For comparison, theoretical upper bounds suggest a103 modes saturate by wave breaking. Thus, the measured constraints only rule out extreme values of the p-g parameters. They also imply that the instability dissipates a1051 erg over the entire inspiral, i.e., less than a few percent of the energy radiated as gravitational waves.