STOCHASTIC GRAVITATIONAL WAVE BACKGROUND FROM NEUTRON STARr-MODE INSTABILITY REVISITED

Abstract

We revisit the possibility and detectability of a stochastic gravitational wave (GW) background produced by a cosmological population of newborn neutron stars (NSs) with r-mode instabilities. The NS formation rate is derived from both observational and simulated cosmic star formation rates (CSFRs). We show that the resultant GW background is insensitive to the choice of CSFR models, but depends strongly on the evolving behavior of CSFR at low redshifts. Nonlinear effects such as differential rotation, suggested to be an unavoidable feature which greatly influences the saturation amplitude of r-mode, are considered to account for GW emission from individual sources. Our results show that the dimensionless energy density Ω GW could have a peak amplitude of ≃ (1 − 3.5) × 10 −8 in the frequency range (200 − 1000) Hz, if the smallest amount of differential rotation corresponding to a saturation amplitude of order unity is assumed. However, such a high mode amplitude is unrealistic as it is known that the maximum value is much smaller and at most 10 −2 . A realistic estimate of Ω GW should be at least 4 orders of magnitude lower (∼ 10 −12 ), which leads to a pessimistic outlook for the detection of r-mode background. We consider different pairs of terrestrial interferometers (IFOs) and compare two approaches to combine multiple IFOs in order to evaluate the detectability of this GW background. Constraints on the total emitted GW energy associated with this mechanism to produce a detectable stochastic background (a SNR of 2.56 with 3-year cross correlation) are ∼ 10 −3 M ⊙ c 2 for two co-located advanced LIGO detectors, and 2×10 −5 M ⊙ c 2 for two Einstein Telescopes. These constraints may also be applicable to alternative GW emission mechanisms related to oscillations or instabilities in NSs depending on the frequency band where most GWs are emitted.

Upper Limits on the Stochastic Gravitational-Wave Background from Advanced LIGO’s First Observing Run

“…These include unresolved compact binary coalescences of both black holes and neutron stars [1][2][3][4][5], rotating neutron stars [6][7][8], supernovae [9][10][11][12], cosmic strings [13][14][15][16], inflationary models [17][18][19][20][21][22][23][24], phase transitions [25][26][27], and the pre-Big Bang scenario [28][29][30][31]. The variety of mechanisms potentially contributing to the background provides the opportunity to study a number of different environments within the Universe.…”

Model of the stochastic gravitational-wave background due to core collapse to black holes

“…Cosmological models include inflationary models [1][2][3][4], models based on cosmic (super)strings [5][6][7][8][9][10], and models of alternative cosmologies [11,12]. Astrophysical models (see [13] for a review) integrate contributions from astrophysical objects across the universe including compact binary coalescences (CBC) of binary neutron stars (BNS) or binary black holes (BBH) [14][15][16][17][18][19][20][21][22][23][24], rotating neutron stars (NSs) [25][26][27][28][29][30][31][32][33][34], magnetars [34][35][36][37][38][39][40], the first stars [41], and white dwarf binaries [42].…”

Improved Upper Limits on the Stochastic Gravitational-Wave Background from 2009–2010 LIGO and Virgo Data

“…Astrophysical contributions to the background might very well dominate in the LIGO and Virgo frequency band. These contributions may include compact binary coalescences [1][2][3][4][5], rotating neutron stars [6][7][8], magnetars [9][10][11], and supernovae [12][13][14][15]. Many mechanisms for generating cosmological contributions to the stochastic background have been postulated as well, such as inflationary models [16][17][18][19][20][21][22][23] and cosmic strings [24][25][26][27].…”

“…Realistic binary rates may lead to a detectable stochastic signal in the advanced detector network. Other astrophysical models (including rotating neutron stars [6][7][8], magnetars [9][10][11], and others) may also contribute to the astrophysical foreground. Astrophysical sources are interesting in their own right.…”