Albino Perego

MAGNETOROTATIONALLY DRIVEN SUPERNOVAE AS THE ORIGIN OF EARLY GALAXY r-PROCESS ELEMENTS?

We examine magnetorotationally driven supernovae as sources of r-process elements in the early Galaxy. On the basis of thermodynamic histories of tracer particles from a three-dimensional magnetohydrodynamical core-collapse supernova model with approximated neutrino transport, we perform nucleosynthesis calculations with and without considering the effects of neutrino absorption reactions on the electron fraction (Ye ) during post-processing. We find that the peak distribution of Ye in the ejecta is shifted from ~0.15 to ~0.17 and broadened toward higher Ye due to neutrino absorption. Nevertheless, in both cases, the second and third peaks of the solar r-process element distribution can be reproduced well. The rare progenitor configuration that was used here, characterized by a high rotation rate and a large magnetic field necessary for the formation of bipolar jets, could naturally provide a site for the strong r-process in agreement with observations of the early Galactic chemical evolution.

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 largescale 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 70 km s −1 ,

On the Orientation and Magnitude of the Black Hole Spin in Galactic Nuclei

Massive black holes (BHs) in galactic nuclei vary their mass M BH and spin vector J BH 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 BH growth evolving contemporarily with mass, spin modulus a, and spin direction. We discover the occurrence of two regimes. An early phase (M BH 107 M ☉) in which rapid alignment of the BH spin direction to the disk angular momentum in each single episode leads to erratic changes in the BH spin orientation and at the same time to large spins (a ~ 0.8). A second phase starts when the BH mass increases above 107 M ☉ and the accretion disks carry less mass and angular momentum relative to the hole. In the absence of a preferential direction, the BHs 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 BH spin can increase up to a ~ 1 for very massive black holes (M BH 108 M ☉), and its direction is stable over the many accretion cycles. We discuss the implications of our results in the realm of the observations of BH spin and jet orientations.

NEUTRINO-DRIVEN WINDS IN THE AFTERMATH OF A NEUTRON STAR MERGER: NUCLEOSYNTHESIS AND ELECTROMAGNETIC TRANSIENTS

We present a comprehensive nucleosynthesis study of the neutrino-driven wind in the aftermath of a binary neutron star merger. Our focus is the initial remnant phase when a massive central neutron star is present. Using tracers from a recent hydrodynamical simulation, we determine total masses and integrated abundances to characterize the composition of unbound matter. We find that the nucleosynthetic yields depend sensitively on both the life time of the massive neutron star and the polar angle. Matter in excess of up to

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

9 \cdot 10^{-3} M_\odot

GW170817: Joint Constraint on the Neutron Star Equation of State from Multimessenger Observations

becomes unbound until

PUSHING CORE-COLLAPSE SUPERNOVAE TO EXPLOSIONS IN SPHERICAL SYMMETRY. I. THE MODEL AND THE CASE OF SN 1987A

\sim 200~{\rm ms}

EFFECTS OF CIRCUMNUCLEAR DISK GAS EVOLUTION ON THE SPIN OF CENTRAL BLACK HOLES

. Due to electron fractions of

NEUTRINO PROCESSES IN PARTIALLY DEGENERATE NEUTRON MATTER

Y_{\rm e} \approx 0.2 - 0.4

The Properties of Short Gamma-Ray Burst Jets Triggered by Neutron Star Mergers

mainly nuclei with mass numbers