Pedro Montero | Harvard University (original) (raw)
Papers by Pedro Montero
We discuss the application of our new three-dimensional fully general relativistic hydrodynamics ... more We discuss the application of our new three-dimensional fully general relativistic hydrodynamics code which uses high-resolution shock-capturing techniques and a conformal traceless formulation of the Einstein equations, to the study of the gravitational collapse of uniformly rotating neutron stars to Kerr black holes. We investigate the dynamics of the matter and of the trapped surfaces. We provide precise measurements of the black-hole mass and spin.
Monthly Notices of The Royal Astronomical Society, 2004
This is the second of a series of papers investigating the oscillation properties of relativistic... more This is the second of a series of papers investigating the oscillation properties of relativistic, non-selfgravitating tori orbiting around black holes. Extending the work done in a Schwarzschild background, we here consider the axisymmetric oscillations of vertically integrated tori in a Kerr spacetime. The tori are modeled with a number of different non-Keplerian distributions of specific angular momentum and we discuss how the oscillation properties depend on these and on the rotation of the central black hole. We first consider a local analysis to highlight the relations between acoustic and epicyclic oscillations in a Kerr spacetime and subsequently perform a global eigenmode analysis to compute the axisymmetric p modes. In analogy with what found in a Schwarzschild background, these modes behave as sound waves that are modified by rotation and are globally trapped in the torus. For constant distributions of specific angular momentum, the eigenfrequencies appear in a sequence 2:3:4:... which is essentially independent of the size of the disc and of the black hole rotation. For non-constant distributions of angular momentum, on the other hand, the sequence depends on the properties of the disc and on the spin of the black hole, becoming harmonic for sufficiently large tori. We also comment on how p modes could explain the high frequency quasi-periodic oscillations observed in low-mass X-ray binaries with a black hole candidate and the properties of an equivalent model in Newtonian physics.
Monthly Notices of The Royal Astronomical Society, 2004
Monthly Notices of The Royal Astronomical Society, 2005
We present a comprehensive numerical study of the dynamics of relativistic axisymmetric accretion... more We present a comprehensive numerical study of the dynamics of relativistic axisymmetric accretion tori with a power-law distribution of specific angular momentum orbiting in the background space–time of a Kerr black hole. By combining general relativistic hydrodynamics simulations with a linear perturbative approach we investigate the main dynamical properties of these objects over a large parameter space. The astrophysical implications of our results extend and improve two interesting results that have been recently reported in the literature. First, the induced quasi-periodic variation of the mass quadrupole moment makes relativistic tori of nuclear matter densities, as those formed during the last stages of binary neutron star mergers, promising sources of gravitational radiation, potentially detectable by interferometric instruments. Secondly, p-mode oscillations in relativistic tori of low rest-mass densities could be used to explain high-frequency quasi-periodic oscillations observed in X-ray binaries containing a black hole candidate under conditions more generic than those considered so far.
Monthly Notices of The Royal Astronomical Society, 2005
Monthly Notices of The Royal Astronomical Society, 2004
This is the second in a series of papers investigating the oscillation properties of relativistic... more This is the second in a series of papers investigating the oscillation properties of relativistic, non-self-gravitating tori orbiting around black holes. Extending the work done in a Schwarzschild background, here we consider the axisymmetric oscillations of vertically integrated tori in a Kerr space-time. The tori are modelled with a number of different non-Keplerian distributions of specific angular momentum, and we discuss how the oscillation properties depend on these and on the rotation of the central black hole. We first consider a local analysis to highlight the relations between acoustic and epicyclic oscillations in a Kerr space-time, and subsequently perform a global eigenmode analysis to compute the axisymmetric p modes. In analogy with what has been found in a Schwarzschild background, these modes behave as sound waves that are modified by rotation and are globally trapped in the torus. For constant distributions of specific angular momentum, the eigenfrequencies appear in a sequence 2:3:4:..., which is essentially independent of the size of the disc and of the black hole rotation. For non-constant distributions of angular momentum, on the other hand, the sequence depends on the properties of the disc and on the spin of the black hole, becoming harmonic for sufficiently large tori. We also comment on how p modes could explain the high-frequency quasi-periodic oscillations observed in low-mass X-ray binaries with a black hole candidate and the properties of an equivalent model in Newtonian physics.
Physical Review D, 2005
We present a new three-dimensional fully general-relativistic hydrodynamics code using high-resol... more We present a new three-dimensional fully general-relativistic hydrodynamics code using high-resolution shock-capturing techniques and a conformal traceless formulation of the Einstein equations. Besides presenting a thorough set of tests which the code passes with very high accuracy, we discuss its application to the study of the gravitational collapse of uniformly rotating neutron stars to Kerr black holes. The initial stellar models are modelled as relativistic polytropes which are either secularly or dynamically unstable and with angular velocities which range from slow rotation to the mass-shedding limit. We investigate the gravitational collapse by carefully studying not only the dynamics of the matter, but also that of the trapped surfaces, i.e. of both the apparent and event horizons formed during the collapse. The use of these surfaces, together with the dynamical horizon framework, allows for a precise measurement of the black-hole mass and spin. The ability to successfully perform these simulations for sufficiently long times relies on excising a region of the computational domain which includes the singularity and is within the apparent horizon. The dynamics of the collapsing matter is strongly influenced by the initial amount of angular momentum in the progenitor star and, for initial models with sufficiently high angular velocities, the collapse can lead to the formation of an unstable disc in differential rotation. All the simulations performed with uniformly rotating initial data and a polytropic or ideal-fluid equation of state show no evidence of shocks or of the presence of matter on stable orbits outside the black hole.
Monthly Notices of The Royal Astronomical Society, 2007
We present a numerical study of the dynamics of magnetized, relativistic, non-self-gravitating, a... more We present a numerical study of the dynamics of magnetized, relativistic, non-self-gravitating, axisymmetric tori orbiting in the background spacetimes of Schwarzschild and Kerr black holes. The initial models have a constant specific angular momentum and are built with a non-zero toroidal magnetic field component, for which equilibrium configurations have recently been obtained. In this work we extend our previous investigations which dealt with purely hydrodynamical thick discs, and study the dynamics of magnetized tori subject to perturbations which, for the values of the magnetic field strength considered here, trigger quasi-periodic oscillations lasting for tens of orbital periods. Overall, we have found that the dynamics of the magnetized tori analyzed is very similar to that found in the corresponding unmagnetized models. The spectral distribution of the eigenfrequencies of oscillation shows the presence of a fundamental p mode and of a series of overtones in a harmonic ratio 2:3:.... These simulations, therefore, extend the validity of the model of Rezzolla et al.(2003a) for explaining the high-frequency QPOs observed in the spectra of LMXBs containing a black-hole candidate also to the case of magnetized discs with purely toroidal magnetic field distribution. If sufficiently compact and massive, these oscillations can also lead to the emission of intense gravitational radiation which is potentially detectable for sources within the Galaxy.
We discuss the application of our new three-dimensional fully general relativistic hydrodynamics ... more We discuss the application of our new three-dimensional fully general relativistic hydrodynamics code which uses high-resolution shock-capturing techniques and a conformal traceless formulation of the Einstein equations, to the study of the gravitational collapse of uniformly rotating neutron stars to Kerr black holes. We investigate the dynamics of the matter and of the trapped surfaces. We provide precise measurements of the black-hole mass and spin.
Monthly Notices of The Royal Astronomical Society, 2004
This is the second of a series of papers investigating the oscillation properties of relativistic... more This is the second of a series of papers investigating the oscillation properties of relativistic, non-selfgravitating tori orbiting around black holes. Extending the work done in a Schwarzschild background, we here consider the axisymmetric oscillations of vertically integrated tori in a Kerr spacetime. The tori are modeled with a number of different non-Keplerian distributions of specific angular momentum and we discuss how the oscillation properties depend on these and on the rotation of the central black hole. We first consider a local analysis to highlight the relations between acoustic and epicyclic oscillations in a Kerr spacetime and subsequently perform a global eigenmode analysis to compute the axisymmetric p modes. In analogy with what found in a Schwarzschild background, these modes behave as sound waves that are modified by rotation and are globally trapped in the torus. For constant distributions of specific angular momentum, the eigenfrequencies appear in a sequence 2:3:4:... which is essentially independent of the size of the disc and of the black hole rotation. For non-constant distributions of angular momentum, on the other hand, the sequence depends on the properties of the disc and on the spin of the black hole, becoming harmonic for sufficiently large tori. We also comment on how p modes could explain the high frequency quasi-periodic oscillations observed in low-mass X-ray binaries with a black hole candidate and the properties of an equivalent model in Newtonian physics.
Monthly Notices of The Royal Astronomical Society, 2004
Monthly Notices of The Royal Astronomical Society, 2005
We present a comprehensive numerical study of the dynamics of relativistic axisymmetric accretion... more We present a comprehensive numerical study of the dynamics of relativistic axisymmetric accretion tori with a power-law distribution of specific angular momentum orbiting in the background space–time of a Kerr black hole. By combining general relativistic hydrodynamics simulations with a linear perturbative approach we investigate the main dynamical properties of these objects over a large parameter space. The astrophysical implications of our results extend and improve two interesting results that have been recently reported in the literature. First, the induced quasi-periodic variation of the mass quadrupole moment makes relativistic tori of nuclear matter densities, as those formed during the last stages of binary neutron star mergers, promising sources of gravitational radiation, potentially detectable by interferometric instruments. Secondly, p-mode oscillations in relativistic tori of low rest-mass densities could be used to explain high-frequency quasi-periodic oscillations observed in X-ray binaries containing a black hole candidate under conditions more generic than those considered so far.
Monthly Notices of The Royal Astronomical Society, 2005
Monthly Notices of The Royal Astronomical Society, 2004
This is the second in a series of papers investigating the oscillation properties of relativistic... more This is the second in a series of papers investigating the oscillation properties of relativistic, non-self-gravitating tori orbiting around black holes. Extending the work done in a Schwarzschild background, here we consider the axisymmetric oscillations of vertically integrated tori in a Kerr space-time. The tori are modelled with a number of different non-Keplerian distributions of specific angular momentum, and we discuss how the oscillation properties depend on these and on the rotation of the central black hole. We first consider a local analysis to highlight the relations between acoustic and epicyclic oscillations in a Kerr space-time, and subsequently perform a global eigenmode analysis to compute the axisymmetric p modes. In analogy with what has been found in a Schwarzschild background, these modes behave as sound waves that are modified by rotation and are globally trapped in the torus. For constant distributions of specific angular momentum, the eigenfrequencies appear in a sequence 2:3:4:..., which is essentially independent of the size of the disc and of the black hole rotation. For non-constant distributions of angular momentum, on the other hand, the sequence depends on the properties of the disc and on the spin of the black hole, becoming harmonic for sufficiently large tori. We also comment on how p modes could explain the high-frequency quasi-periodic oscillations observed in low-mass X-ray binaries with a black hole candidate and the properties of an equivalent model in Newtonian physics.
Physical Review D, 2005
We present a new three-dimensional fully general-relativistic hydrodynamics code using high-resol... more We present a new three-dimensional fully general-relativistic hydrodynamics code using high-resolution shock-capturing techniques and a conformal traceless formulation of the Einstein equations. Besides presenting a thorough set of tests which the code passes with very high accuracy, we discuss its application to the study of the gravitational collapse of uniformly rotating neutron stars to Kerr black holes. The initial stellar models are modelled as relativistic polytropes which are either secularly or dynamically unstable and with angular velocities which range from slow rotation to the mass-shedding limit. We investigate the gravitational collapse by carefully studying not only the dynamics of the matter, but also that of the trapped surfaces, i.e. of both the apparent and event horizons formed during the collapse. The use of these surfaces, together with the dynamical horizon framework, allows for a precise measurement of the black-hole mass and spin. The ability to successfully perform these simulations for sufficiently long times relies on excising a region of the computational domain which includes the singularity and is within the apparent horizon. The dynamics of the collapsing matter is strongly influenced by the initial amount of angular momentum in the progenitor star and, for initial models with sufficiently high angular velocities, the collapse can lead to the formation of an unstable disc in differential rotation. All the simulations performed with uniformly rotating initial data and a polytropic or ideal-fluid equation of state show no evidence of shocks or of the presence of matter on stable orbits outside the black hole.
Monthly Notices of The Royal Astronomical Society, 2007
We present a numerical study of the dynamics of magnetized, relativistic, non-self-gravitating, a... more We present a numerical study of the dynamics of magnetized, relativistic, non-self-gravitating, axisymmetric tori orbiting in the background spacetimes of Schwarzschild and Kerr black holes. The initial models have a constant specific angular momentum and are built with a non-zero toroidal magnetic field component, for which equilibrium configurations have recently been obtained. In this work we extend our previous investigations which dealt with purely hydrodynamical thick discs, and study the dynamics of magnetized tori subject to perturbations which, for the values of the magnetic field strength considered here, trigger quasi-periodic oscillations lasting for tens of orbital periods. Overall, we have found that the dynamics of the magnetized tori analyzed is very similar to that found in the corresponding unmagnetized models. The spectral distribution of the eigenfrequencies of oscillation shows the presence of a fundamental p mode and of a series of overtones in a harmonic ratio 2:3:.... These simulations, therefore, extend the validity of the model of Rezzolla et al.(2003a) for explaining the high-frequency QPOs observed in the spectra of LMXBs containing a black-hole candidate also to the case of magnetized discs with purely toroidal magnetic field distribution. If sufficiently compact and massive, these oscillations can also lead to the emission of intense gravitational radiation which is potentially detectable for sources within the Galaxy.