Shmuel Balberg

SUPERLUMINOUS LIGHT CURVES FROM SUPERNOVAE EXPLODING IN A DENSE WIND

Observations from the last decade have indicated the existence of a general class of superluminous supernovae (SLSNe), in which the peak luminosity exceeds 1044 erg s–1. Here we focus on a subclass of these events, where the light curve is also tens of days wide, so the total radiated energy is of order 1051 erg. If the origin of these SLSNe is a core-collapse-driven explosion of a massive star, then the mechanism that converts the explosion energy into radiation must be very efficient (much more than in typical core-collapse SNe, where this efficiency is of order 1%). We examine the scenario where the radiated luminosity is due to efficient conversion of kinetic energy of the ejected stellar envelope into radiation by interaction with an optically thick, pre-existing circumstellar material, presumably the product of a steady wind from the progenitor. We base the analysis on analytical derivations of various limits, and on a simple, numerically solved, hydrodynamic diffusion model, which allows us to explore the regime of interest, which does not correspond to the analytical limits. In our results, we identify the qualitative behavior of the observable light curves, and relate them to the parameters of the wind. We specifically show that a wide and superluminous supernova requires the mass of the relevant wind material to be comparable to that of the ejected material from the exploding progenitor. We find the wind parameters that explain the peak luminosity and width of the bolometric light curves of three particular SLSNe, namely, SN 2005ap, SN 2006gy, and SN 2010gx, and show that they are best fitted with a wind that extends to a radius of order 1015 cm. These results serve as an additional indication that at least some SLSNe may be powered by interaction of the ejected material with a steady wind of similar mass.

Gravothermal collapse of self-interacting dark matter halos and the origin of massive black holes

Black hole formation is an inevitable consequence of relativistic core collapse following the gravothermal catastrophe in self-interacting dark matter (SIDM) halos. Very massive SIDM halos form supermassive black holes (SMBHs) > or about 10(6)M(middle dot in circle) directly. Smaller halos believed to form by redshift z = 5 produce seed black holes of (10(2)-10(3))M(middle dot in circle) which can merge and/or accrete to reach the observational SMBH range. This scenario for SMBH formation requires no baryons, no prior star formation, and no other black hole seed mechanism.

Implications of Hyperon Pairing for Cooling of Neutron Stars

The implications of hyperon pairing for the thermal evolution of neutron stars containing hyperons are investigated. The outcomes of cooling simulations are compared for neutron star models composed only of nucleons and leptons, models including hyperons, and models including pairing of hyperons. We show that lambda and neutron pairing suppresses all possible fast neutrino emission processes in not too massive neutron stars. The inclusion of lambda pairing yields better agreement with X-ray observations of pulsars. Particularly, the surface temperatures deduced from X-ray observations within the hydrogen atmosphere model are more consistent with the thermal history of neutron stars containing hyperons, if the critical temperature for the onset of lambda and nucleon pairing is not too small.

Black hole emergence in supernovae

If a black hole formed in a core-collapse supernova is accreting material from the base of the envelope, the accretion luminosity could be observable in the supernova light curve. Here we continue the study of matter fallback onto a black hole in the wake of a supernova and examine realistic supernovae models that allow for an early emergence of the accretion luminosity. Such cases may provide a direct observational identification of the black hole formed in the aftermath of the explosion. Our approach combines analytic estimates and fully relativistic, radiation-hydrodynamic numerical computations. We employ a numerical hydrodynamical scaling technique to accommodate the diverse range of dynamical timescales in a single simulation. We find that while in typical Type II supernovae heating by radioactive decays dominates the late-time light curve, low-energy explosions of more massive stars should provide an important exception where the accretion luminosity will emerge while it is still relatively large. Our main focus is on the only current candidate for such an observation, the very unusual SN 1997D. Owing to the low energy of the explosion and the very small (2 × 10-3 M☉) inferred mass of 56Co in the ejected envelope, we find that accretion should become the dominant source of its luminosity during the year 2000. The total luminosity at emergence is expected to lie in the range 0.5-3 × 1036 ergs s-1, potentially detectable with the Hubble Space Telescope. We also discuss the more favorable case of explosions that eject negligible amounts of radioactive isotopes and find that the black hole is likely to emerge a few tens of days after the explosion, with a luminosity of ~1037 ergs s-1.

Shock Revival in Core-Collapse Supernovae: A Phase-Diagram Analysis

We examine the conditions for the revival of the stalled accretion shock in core-collapse supernovae, in the context of the neutrino heating mechanism. We combine one dimensional simulations of the shock revival process with a derivation of a quasi-stationary approximation, which is both accurate and efficient in predicting the flow. In particular, this approach is used to explore how the evolution of the system depends on the shock radius,

Galaxy evolution: modelling the role of non-thermal pressure in the interstellar medium

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Critical conditions for core-collapse supernovae.

, and velocity,

Comment on "Strangelets as cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff".

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Neutron Stars with a Stable, Light Supersymmetric Baryon

(in addition to other global properties of the system). We do so through a phase space analysis of the shock acceleration,

The fading of supernova 1997D

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