Gravitational-wave asteroseismology with fundamental modes from compact binary inspirals

Abstract

Gravitational waves (GWs) from binary neutron stars encode unique information about ultradense matter through characterisic signatures associated with a variety of phenomena including tidal effects during the inspiral. The main tidal signature depends predominantly on the equation of state (EoS)-related tidal deformability parameter Λ, but at late times is also characterised by the frequency of the star's fundamental oscillation mode (f-mode). In General Relativity and for nuclear matter, Λ and the f-modes are related by universal relations which may not hold for alternative theories of gravity or exotic matter. Independently measuring Λ and the f-mode frequency enables tests of gravity and the nature of compact binaries. Here we present directly measured constraints on the f-mode frequencies of the companions of GW170817. We also show that future GW detector networks will measure fmode frequencies to within tens of Hz, enabling precision GW asteroseismology with binary inspiral signals alone.

Neutron-star tidal deformability and equation-of-state constraints

“…Another effect of interest is the potential resonant excitation of different neutron star modes driven by the orbital motion [338,339]. In spite of its high resonance frequency, O(1000)Hz, an f-mode excitation could be detected in the future [340][341][342], potentially aided by orbital eccentricity [343] or neutron star spins [344]. A search for a proposed nonresonant mode coupling [345][346][347][348] in GW170817 and GW190425 was inconclusive [32,349].…”

Excitation of f -modes during mergers of spinning binary neutron star

“…where the coefficients V and I s xy ¼ I xx þ I yy are determined by the normalization condition equation (14). Here I xx and I yy are the components of the moment of inertia…”

“…The detection of gravitational waves (GWs) and their electromagnetic counterparts from binary neutron star (BNS) coalescence GW170817 [1][2][3][4], as well as the recent event GW190425 [5], has started a new approach to study the physics of NSs. The observations have already provided new constraints on tidal deformabilities [6][7][8][9], the maximum mass [7,[10][11][12][13], radii [6,9], and f-mode frequencies [14] of NSs. With the improvement of detector sensitivity, more BNS coalescence detections are expected for the near future [15][16][17][18].…”

Detecting resonant tidal excitations of Rossby modes in coalescing neutron-star binaries with third-generation gravitational-wave detectors

“…Gravitational-wave (GW) astronomy recently provided us a new way to study neutron-star (NS) physics, with events GW170817 [1,2] and GW190425 [3] already imposing new constraints on NS properties [4][5][6][7][8][9][10][11][12]. With future upgrades for Advanced LIGO and Virgo [13][14][15][16][17][18][19][20][21][22][23][24], LIGO-India [25], and KAGRA [26,27], as well as thirdgeneration detectors like the Einstein Telescope [28][29][30][31] and the Cosmic Explorer (CE) [32,33], we expect to detect more events, as well as to achieve much higher signal-tonoise ratios [34].…”