On the orientation and magnitude of the black hole spin in galactic nuclei

Massive black holes in galactic nuclei vary their mass M and spin vector J due to accretion. In this study we relax, for the first time, the assumption that accretion can be either chaotic, i.e. when the accretion episodes are randomly and isotropically oriented, or coherent, i.e. when they occur all in a preferred plane. Instead, we consider different degrees of anisotropy in the fueling, never confining to accretion events on a fixed direction. We follow the black hole growth evolving contemporarily mass, spin modulus a and spin direction. We discover the occurrence of two regimes. An early phase (M <~ 10 million solar masses) in which rapid alignment of the black hole spin direction to the disk angular momentum in each single episode leads to erratic changes in the black hole spin orientation and at the same time to large spins (a ~ 0.8). A second phase starts when the black hole mass increases above >~ 10 million solar masses and the accretion disks carry less mass and angular momentum relatively to the hole. In the absence of a preferential direction the black holes tend to spin-down in this phase. However, when a modest degree of anisotropy in the fueling process (still far from being coherent) is present, the black hole spin can increase up to a ~ 1 for very massive black holes (M >~ 100 million solar masses), and its direction is stable over the many accretion cycles. We discuss the implications that our results have in the realm of the observations of black hole spin and jet orientations.Comment: 14 pages, 7 figures, accepted for publication in Ap

A path to radio-loudness through gas-poor galaxy mergers and the role of retrograde accretion

In this proceeding we explore a pathway to radio-loudness under the hypothesis that retrograde accretion onto giant spinning black holes leads to the launch of powerful jets, as seen in radio loud QSOs and recently in LAT/Fermi and BAT/Swift Blazars. Counter-rotation of the accretion disc relative to the BH spin is here associated to gas-poor galaxy mergers progenitors of giant (missing-light) ellipticals. The occurrence of retrograde accretion enters as unifying element that may account for the radio-loudness/galaxy morphology dichotomy observed in AGN.Comment: To appear in the proceedings of the conference "Accretion and Ejection in AGN: A global view, June 22-26 2009 - Como, Italy

Mass and spin co-evolution during the alignment of a black hole in a warped accretion disc

In this paper, we explore the gravitomagnetic interaction of a black hole (BH) with a misaligned accretion disc to study BH spin precession and alignment jointly with BH mass MBH and spin parameter a evolution, under the assumption that the disc is continually fed, in its outer region, by matter with angular momentum fixed on a given direction . We develop an iterative scheme based on the adiabatic approximation to study the BH-disc co-evolution: in this approach, the accretion disc transits through a sequence of quasi-steady warped states (Bardeen-Petterson effect) and interacts with the BH until the spin JBH aligns with . For a BH aligning with a corotating disc, the fractional increase in mass is typically less than a few per cent, while the spin modulus can increase up to a few tens of per cent. The alignment time-scale is of ∼105-106 yr for a maximally rotating BH accreting at the Eddington rate. BH-disc alignment from an initially counter-rotating disc tends to be more efficient compared to the specular corotating case due to the asymmetry seeded in the Kerr metric: counter-rotating matter carries a larger and opposite angular momentum when crossing the innermost stable orbit, so that the spin modulus decreases faster and so the relative inclination angl

A Lagrangian PFEM approach tothe numerical simulation of 3D large scale landslides impinging in water reservoirs

Landslides are exceptional natural hazards that can generate extensive damage to structures and infrastructures causing a large number of casualties. A particularly critical condition occurs when the landslide impinges in water reservoirs generating high waves. This work proposes a numerical tool to simulate the macroscopic behavior of a propagating landslide. The Particle Finite Element Method (PFEM) is here used and adapted to the specific case of landslide runout. The Lagrangian Navier-Stokes equations of incompressible fluids are used to describe the macroscopic landslide behavior. A rigid-visco-plastic law with a pressure dependent threshold, typical of a non-Newtonian, Bingham-like fluid, is used to characterize the constitutive behavior of the flowing material. Special attention is devoted to the definition of ad-hoc pressure-dependent slip boundary conditions at the interface between the flowing mass and the basal surface to better represent the real landslide-slope interaction. The proposed approach has been validated against numerical benchmarks and small scale experimental tests, showing a good agreement with the physical measurements. Real case scenarios have also been considered. 3D geometries of critical sites, where landslides have occurred, have been reconstructed allowing for the simulation of large scale real landslide runouts. Results are compared with post-event images and measurements, showing the accuracy and the capability of the method

Investigating Social Exclusion in Late Prehistoric Italy: Preliminary Results of the ‘‘IN or OUT’’ Project (PHASE 1)

This report presents the preliminary results of the ‘‘IN or OUT’’ Project, a collaborative, interdisciplinary effort which aims to investigate social exclusion, marginality and the adoption of anomalous funerary rites in late prehistoric Italy. In particular, this contribution explores the incidence and meaning of practices of ritual marginalisation and funerary deviancy in the region of Veneto between the Bronze Age and the early Iron Age period

Neutrino processes in partially degenerate neutron matter

We investigate neutrino processes for conditions reached in simulations of core-collapse supernovae. Where neutrino-matter interactions play an important role, matter is partially degenerate, and we extend earlier work that addressed the degenerate regime. We derive expressions for the spin structure factor in neutron matter, which is a key quantity required for evaluating rates of neutrino processes. We show that, for essentially all conditions encountered in the post-bounce phase of core-collapse supernovae, it is a very good approximation to calculate the spin relaxation rates in the nondegenerate limit. We calculate spin relaxation rates based on chiral effective field theory interactions and find that they are typically a factor of two smaller than those obtained using the standard one-pion-exchange interaction alone.Comment: 41 pages, 9 figures, NORDITA-2011-116; added comparison figures and fit function for use in simulations, to appear in Astrophys.

Dual black holes in merger remnants - II. Spin evolution and gravitational recoil

Using high-resolution hydrodynamical simulations, we explore the spin evolution of massive dual black holes orbiting inside a circumnuclear disc, relic of a gas-rich galaxy merger. The black holes spiral inwards from initially eccentric co- or counter-rotating coplanar orbits relative to the disc's rotation, and accrete gas that is carrying a net angular momentum. As the black hole mass grows, its spin changes in strength and direction due to its gravito-magnetic coupling with the small-scale accretion disc. We find that the black hole spins loose memory of their initial orientation, as accretion torques suffice to align the spins with the angular momentum of their orbit on a short time-scale (≲1-2 Myr). A residual off-set in the spin direction relative to the orbital angular momentum remains, at the level of ≲10° for the case of a cold disc, and ≲30° for a warmer disc. Alignment in a cooler disc is more effective due to the higher coherence of the accretion flow near each black hole that reflects the large-scale coherence of the disc's rotation. If the massive black holes coalesce preserving the spin directions set after formation of a Keplerian binary, the relic black hole resulting from their coalescence receives a relatively small gravitational recoil. The distribution of recoil velocities inferred from a simulated sample of massive black hole binaries has median , much smaller than the median resulting from an isotropic distribution of spin

Explicit dynamics simulation of blade cutting of thin elastoplastic shells using "directional" cohesive elements in solid-shell finite element models

The intentional or accidental cutting of thin shell structures by means of a sharp object is of interest in many engineering applications. The process of cutting involves several types of nonlinearities, such as large deformations, contact, crack propagation and, in the case of laminated shells, delamination. In addition to these, a special difficulty is represented by the blade sharpness, whose accurate geometric resolution would require meshes with characteristic size of the order of the blade curvature radius. A computational finite element approach for the simulation of blade cutting of thin shells is proposed and discussed. The approach is developed in an explicit dynamics framework. Solid-shell elements are used for the discretization, in view of possible future inclusion in the model of delamination processes. Since a sharp blade can interfere with the transmission of cohesive forces between the crack flanks in the cohesive process zone, standard cohesive interface elements are not suited for the simulation of this type of problems unless extremely fine meshes, with characteristic size comparable to the blade curvature radius, are used. To circumvent the problem, the use of a new type of directional cohesive interface element, previously proposed for the simulation of crack propagation in elastic shells, is further developed and reformulated for application to the cutting of elastoplastic thin structures, discretized by solid-shell elements. The proposed approach is validated by means of application to several cutting problems of engineering interest

Pushing 1D CCSNe to explosions: model and SN 1987A

We report on a method, PUSH, for triggering core-collapse supernova explosions of massive stars in spherical symmetry. We explore basic explosion properties and calibrate PUSH such that the observables of SN1987A are reproduced. Our simulations are based on the general relativistic hydrodynamics code AGILE combined with the detailed neutrino transport scheme IDSA for electron neutrinos and ALS for the muon and tau neutrinos. To trigger explosions in the otherwise non-exploding simulations, we rely on the neutrino-driven mechanism. The PUSH method locally increases the energy deposition in the gain region through energy deposition by the heavy neutrino flavors. Our setup allows us to model the explosion for several seconds after core bounce. We explore the progenitor range 18-21M$_{\odot}$. Our studies reveal a distinction between high compactness (HC) and low compactness (LC) progenitor models, where LC models tend to explore earlier, with a lower explosion energy, and with a lower remnant mass. HC models are needed to obtain explosion energies around 1 Bethe, as observed for SN1987A. However, all the models with sufficiently high explosion energy overproduce $^{56}$Ni. We conclude that fallback is needed to reproduce the observed nucleosynthesis yields. The nucleosynthesis yields of $^{57-58}$Ni depend sensitively on the electron fraction and on the location of the mass cut with respect to the initial shell structure of the progenitor star. We identify a progenitor and a suitable set of PUSH parameters that fit the explosion properties of SN1987A when assuming 0.1M$_{\odot}$ of fallback. We predict a neutron star with a gravitational mass of 1.50M$_{\odot}$. We find correlations between explosion properties and the compactness of the progenitor model in the explored progenitors. However, a more complete analysis will require the exploration of a larger set of progenitors with PUSH.Comment: revised version as accepted by ApJ (results unchanged, text modified for clarification, a few references added); 26 pages, 20 figure