A new gravitational-wave signature of low-T/|W| instability in rapidly rotating stellar core collapse

Abstract

We present results from a full general relativistic three-dimensional hydrodynamics simulation of rapidly rotating core-collapse of a 70 M star with three-flavor spectral neutrino transport. To see clearly the impact of rotation on both the dynamics and gravitational-wave (GW) emission, the initial central angular velocity of 2.0 rad s −1 is imposed. We find a strong GW emission that originates from the growth of the one-and twoarmed spiral waves extending from the nascent proto-neutron star (PNS). The GW spectrogram shows several unique features that are produced by the non-axisymmetric instabilities. After bounce, the spectrogram first shows a transient quasi-periodic time modulation at ∼ 450 Hz. In the second active phase, it again shows the quasi-periodic modulation but with the peak frequency increasing with time, which continues until the final simulation time (∼ 270 ms after bounce). From our detailed analysis, such features can be well explained by a combination of the so-called low-T /|W | instability and the PNS core contraction. We point out that the next generation interferometers such as Einstein Telescope and Cosmic Explorer could make it possible to detect these GW signals up to ∼ Mpc distance scales.

Characteristic time variability of gravitational-wave and neutrino signals from three-dimensional simulations of non-rotating and rapidly rotating stellar core collapse

“…3. As we have already shown in Shibagaki et al (2020), the onset of the second low-/| | instability is associated with the generation of the two-armed spiral flow in the vicinity of the PNS.…”

“…Note that the evaluation of ℎ char in this paper is different from that in Kuroda et al(2014)andShibagaki et al (2020). The difference is, for example, that the angle-average was partly taken in the previous estimate.…”

“…In this phase, the peak frequency of the GW increases from 300 Hz to 400 Hz with time. The peak frequency of the quasi-periodic GWs seen in the above two rotating models corresponds to the rotation frequency of the PNS, and the increase of the peak frequency can be interpreted as due to the gradual PNS contraction (Shibagaki et al 2020). Both of the two models commonly show that the plus mode of the quasi-periodic GW observed in the equatorial plane is roughly two times bigger than the plus and cross modes observed in the polar direction, and the cross mode observed in the equatorial plane is much smaller than the plus mode.…”

Pulsational pair-instability supernovae: gravitational collapse, black-hole formation, and beyond

“…These effects influence the possibility of neutrino-driven shock expansion in multiple ways and often enable explosions in 2D when 3D simulations yield failures (see, e.g., Melson et al 2015b;Summa et al 2018). Another generically 3D effect concerns rapidly rotating models, which can develop equatorial explosions in 3D because of the support by SASI spiral modes (Summa et al 2018) or other triaxial spiral waves (e.g., Shibagaki et al 2020). Such phenomena 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 do not exist in 2D.…”

Instabilities in neutron-star postmerger remnants

“…. represents an angular average at a specific radius in the equatorial plane [52]. The computational domain is divided into two parts, approximately representing the neutron star interior and the surrounding low-density medium (the atmosphere).…”