We analyze the properties of the gravitational wave signal emitted after the merger of a binary neutron star system when the remnant survives for more than a 80 ms (and up to 140 ms). We employ four different piecewise polytropic equations of state supplemented by an ideal fluid thermal component. We find that the postmerger phase can be subdivided into three phases: an early postmerger phase (where the quadrupole mode and a few subdominant features are active), the intermediate postmerger phase (where only the quadrupole mode is active) and the late postmerger phase (where convective instabilities trigger inertial modes). The inertial modes have frequencies somewhat smaller than the quadrupole modes. In one model, we find an interesting association of a corotation of the quadrupole mode in parts of the star with a revival of its amplitude. The gravitational wave emission of inertial modes in the late postmerger phase is concentrated in a narrow frequency region and is potentially detectable by the planned third-generation detectors. This allows for the possibility of probing not only the cold part of the equation of state, but also its dependence on finite temperature. In view of these results, it will be important to investigate the impact of various type of viscosities on the potential excitation of inertial modes in binary neutron star merger remnants.

We present the first very long-term simulations (extending up to $\sim 140\mathrm{ms}$ after merger) of binary neutron star mergers with piecewise polytropic equations of state and in full general relativity. Our simulations reveal that, at a time of 30–50 ms after merger, parts of the star become convectively unstable, which triggers the excitation of inertial modes. The excited inertial modes are sustained up to several tens of milliseconds and are potentially observable by the planned third-generation gravitational-wave detectors at frequencies of a few kilohertz. Since inertial modes depend on the rotation rate of the star and they are triggered by a convective instability in the postmerger remnant, their detection in gravitational waves will provide a unique opportunity to probe the rotational and thermal state of the merger remnant. In addition, our findings have implications for the long-term evolution and stability of binary neutron star remnants.

Petroleum, also known as crude oil, is a natural, non-renewable, and essential energy resource. Its extraction and transportation require specific precautions/recommendations to prevent or mitigate potential emergency scenarios, and pollution of soil, air, and water resources. One of the safest ways of transporting crude oil is through pipelines. However, they are subject to corrosion that may lead to leaks that cause severe environmental and water pollution. In this paper, we investigate the migration of petroleum in a scenario mimicking a pipeline leakage (with the pipeline included in the numerical simulation) and the consequent spread of the contaminant in the environment. We use the numerical code CactusHydro, which accurately resolves the sharp discontinuities and temporal dynamics of three-phase fluid flow and thereby accurately tracks contaminant migration in space and time through a variably saturated zone with variable permeability and porosity. We analyze various scenarios encompassing different climatic conditions, including rainfall-induced water saturation, in the variable-saturation porous medium zone and different porosity values, for a total of sixteen transient numerical simulations. Hydraulic conductivity is linked to saturation and provides information on the type of porous soil that facilitates contaminant migration. Also, the porosity can vehicle more or less rapidly its vertical movement in the unsaturated zone. The numerical results show that the vertical migration of the petroleum is primarily driven by the high pressure within the pipeline, since the contaminant has a very limited mobility. Moreover, hydraulic conductivity and porosity play important roles in petroleum migration. Our results suggest that, for crude oil, the distribution of leaked oil may not extend below 2 meters in elevation within 10 days. Our conclusions show that certain types of soil are more adaptable at preventing possible spill migration and can be helpful in constructing pipeline paths that avoid or reduce pollution.