Gravitational wave burst signal from core collapse of rotating stars

Abstract

We present results from detailed general relativistic simulations of stellar core collapse to a protoneutron star, using two different microphysical nonzero-temperature nuclear equations of state as well as an approximate description of deleptonization during the collapse phase. Investigating a wide variety of rotation rates and profiles as well as masses of the progenitor stars and both equations of state, we confirm in this very general setup the recent finding that a generic gravitational wave burst signal is associated with core bounce, already known as type I in the literature. The previously suggested type II (or "multiple-bounce") waveform morphology does not occur. Despite this reduction to a single waveform type, we demonstrate that it is still possible to constrain the progenitor and postbounce rotation based on a combination of the maximum signal amplitude and the peak frequency of the emitted gravitational wave burst. Our models include to sufficient accuracy the currently known necessary physics for the collapse and bounce phase of core-collapse supernovae, yielding accurate and reliable gravitational wave signal templates for gravitational wave data analysis. In addition, we assess the possiblity of nonaxisymmetric instabilities in rotating nascent proto-neutron stars. We find strong evidence that in an iron core-collapse event the postbounce core cannot reach sufficiently rapid rotation to become subject to a classical bar-mode instability. However, many of our postbounce core models exhibit sufficiently rapid and differential rotation to become subject to the recently discovered dynamical instability at low rotation rates.

Sources of Gravitational Waves: Theory and Observations

“…Thus the time scale for collapse is τ FF ∼ 2 ms and the frequency of GWs would be f ∼ τ −1 FF ∼ 500 Hz. Numerical simulations also reveal that the time domain waveform is a short burst and the energy in the burst is spread over a frequency range of 200 Hz to 1 kHz, with the peak of the radiation at f peak 500 Hz [429,430]. If a fraction ∼ 10 −8 of the rest mass energy of the star is converted to GWs then the characteristic amplitude of the signal would be h c ∼ 2 × 10 −22 Hz −1/2 .…”

Equation-of-state dependent features in shock-oscillation modulated neutrino and gravitational-wave signals from supernovae

“…In particular the infall and bounce phases, which are theoretically relatively well understood parts of the evolution, have received a lot of interest, because a strong and characteristic signature could make them a promising source of a detectable gravitational-wave burst (for a review-like introduction to the subject and a nearly complete list of publications, see Dimmelmeier et al 2008). For this to be the case, the core of the progenitor star must develop a sufficiently large deformation during its infall, and for that it must rotate enough rapidly.…”

Gravitational wave extraction in simulations of rotating stellar core collapse

“…Of the entire ensemble of potential GW emission processes in stellar collapse, rotating core collapse and bounce is arguably the simplest and yields the cleanest signal, depending only on rotation, on the nuclear EOS, and on the mass of the inner core at bounce [5]. Moreover, 3D studies have shown that collapsing iron cores with rotation rates in the range of what is physically plausible stay axisymmetric throughout the collapse phase and develop nonaxisymmetric dynamics only after bounce [4,6,17].…”

“…Rotation, centrifugally deforming the inner core to oblate shape, is an obvious source of such quadrupole asymmetry and rotating core collapse and bounce is the most extensively studied GW emission process in stellar collapse (see, e.g., [4][5][6][7][8][9] for recent studies and references therein). Alternatively, asymmetries in collapse may arise from perturbations, e.g., due to large convective plumes in the final phase of core nuclear burning, and may lead to GW emission at bounce and/or seed GW-emitting prompt postbounce convection [3,10,11].…”