Narrow Results

What the progenitors of Type Ia supernovae (SNe Ia) are, whether they are near-Chandrasekhar mass or sub-Chandrasekhar mass white dwarfs, has been the matter of debate for decades. Various observational hints are supporting both models as the main progenitors. In this paper, we review the explosion physics and the chemical abundance patterns of SNe Ia from these two classes of progenitors. We will discuss how the observational data of SNe Ia, their remnants, the Milky Way Galaxy, and galactic clusters can help us to determine the essential features where numerical models of SNe Ia need to match.

Core-collapse supernovae produce copious low-energy neutrinos and are also predicted to radiate gravitational waves. These two messengers can give us information regarding the explosion mechanism. The gravitational wave detection from these events are still elusive even with the already advanced detectors. Here we give a concise and timely introduction to a new method that combines triggers from GW and neutrino observatories; more details shall be given in a forthcoming paper.

The spectral energy distribution (SED) sequence for type Ia supernovae (SN Ia) is modeled by an artificial neural network. The SN Ia luminosity is characterized as a function of phase, wavelength, a color parameter and a decline rate parameter. After training and testing the neural network, the SED sequence could give both the spectrum with wavelength range from 3000 Åto 8000 Åand the light curve with phase from 20 days before to 50 days after the maximum luminosity for the supernovae with different colors and decline rates. Therefore, we call this the Artificial Neural Network Spectral Light Curve Template (ANNSLCT) model. We retrain the Joint Light-curve Analysis (JLA) supernova sample by using the ANNSLCT model and obtain the parameters for each supernova to make a constraint on the cosmological $\mathrm{\Lambda }$CDM model. We find that the best fitting values of these parameters are very close to those from the JLA sample trained with the Spectral Adaptive Lightcurve Template 2 (SALT2) model. It is expectable that the ANNSLCT model has potential to analyze more SN Ia multi-color light curves measured in future observation projects.

It has been known since 1987 that many features of supernovae cannot be described by the spherically-symmetric picture assumed in one-dimensional explosion models. However, the study of the propagation of a supernova shock through a star in more than one spatial dimension is still in its infancy. Understanding this propagation, and the mixing associated with it, is critical for determining accurate supernova yields and correctly interpreting observations based on those yields — from gamma-rays and overall light curves produced in supernova explosions to the abundances of isotopes studied in stars. Here we review the current state-of-the-art in this field. By necessity, this problem is computational and therefore provides an ideal setting to discuss how verification and validation techniques can play an important role in taking full advantage of the results from numerical simulations. We discuss this problem using the full arsenal of verification and validation techniques currently available.

As a solution to the well-known problem that the shock wave potentially responsible for the explosion of a supernova actually tends to stall, we propose a new energy source arising from our model for dark matter. Our earlier model proposed that dark matter should consist of cm-large white dwarf-like objects kept together by a skin separating two different sorts of vacua. These dark matter balls or pearls will collect in the middle of any star throughout its lifetime. At some stage during the development of a supernova, the balls will begin to take in neutrons and then other surrounding material. By passing into a ball nucleons fall through a potential of order 10 MeV, causing a severe production of heat — of order 10 foe for a solar mass of material eaten by the balls. The temperature in the iron core will thereby be raised, splitting up the iron into smaller nuclei. This provides a mechanism for reviving the shock wave when it arrives and making the supernova explosion really occur. The onset of the heating due to the dark matter balls would at first stop the collapse of the supernova progenitor. This opens up the possibility of there being two collapses giving two neutrino outbursts, as apparently seen in the supernova SN1987A — one in Mont Blanc and one 4 h 43 min later in both IMB and Kamiokande.

We review the recent progress in understanding the nature of gamma-ray bursts (GRBs). The occurrence of GRB is explained by the Induced Gravitational Collapse (IGC) in FeCO Core–Neutron star binaries and Neutron star–Neutron star binary mergers, both processes occur within binary system progenitors. Making use of this most unexpected new paradigm, with the fundamental implications by the neutron star (NS) critical mass, we find that different initial configurations of binary systems lead to different GRB families with specific new physical predictions confirmed by observations.

Neutrino-induced reactions are a basic ingredient in astrophysical processes like star evolution. The existence of neutrino oscillations affects the rate of nuclear electroweak decays which participates in the chain of events that determines the fate of the star. Among the processes of interest, the production of heavy elements in core-collapse supernovae is strongly dependent upon neutrino properties, like the mixing between different species of neutrinos. In this work, we study the effects of neutrino oscillations upon the electron fraction as a function of the neutrino mixing parameters, for two schemes: the $1+1$-scheme (one active neutrino and one sterile neutrino) and the $2+1$-scheme (two active neutrinos and one sterile neutrino). We have performed this analysis considering a core-collapse supernovae and determined the physical conditions needed to activate the nuclear reaction chains involved in the r-process. We found that the interactions of the neutrinos with matter and among themselves and the initial amount of sterile neutrinos in the neutrino-sphere might change the electron fraction, therefore affecting the onset of the r-process. We have set constrains on the active-sterile neutrino mixing parameters. They are the square-mass-difference $\mathrm{\Delta }{m}_{14}^2$, the mixing angle ${sin}^{2}2{𝜃}_{14}$, and the hindrance factor ${\xi }_s$ for the occupation of sterile neutrinos. The calculations have been performed for different values of $X_{\alpha }$, which is the fraction of $\alpha$-particles. For $X_{\alpha }=0$ the r-process is taking place if $\mathrm{\Delta }{m}_{14}^2\ge 2{\mathrm{\text{eV}}}^2$, ${sin}^{2}2{𝜃}_{14}<0.8$ and ${\xi }_s<0.5$. For larger values of $X_{\alpha }$ the region of parameters is strongly reduced. The present results are compared to results available in the literature.

In this paper, a general formula of the symmetry energy for many-body interaction is proposed and the commonly used two-body interaction symmetry energy is recovered. Within Landau's theory (Lt), we generalize two equations of state (EoS) CCSδ3 and CCSδ5 to asymmetric nuclear matter. We assume that the density and density difference between protons and neutrons divided by their sum are order parameters. We use different EoS to study neutron stars by solving the TOV equations. We demonstrate that different EoS give different mass and radius relation for neutron stars even when they have exactly the same ground state (gs) properties (E/A, ρ₀, K, S, L and K_sym). Furthermore, for one EoS we change K_sym and fix all the other gs parameters. We find that for some K_sym the EoS becomes unstable at high density even for neutron matter. This suggests that a neutron star (NS) can exist below and above the instability region but in different states: a quark gluon plasma (QGP) at high density and baryonic matter at low density. If the star's central density is in the instability region, then we associate these conditions to the occurrence of supernovae (SN).

Nuclear physics is an indispensable input for the investigation of high energy astrophysical phenomena involving compact objects. In this paper I take a gravitational collapse of massive stars as an example and show how the macroscopic dynamics is influenced by the properties of nuclei and nuclear matter. I will discuss two topics that are rather independent of each other. The first one is the interplay of neutrino-nuclei inelastic scatterings and the standing accretion shock instability in the core of core collapse supernovae and the second is concerning the neutrino emissions from black hole formations and their dependence on the equation of state at very high densities. In the latter, I will also demonstrate that future astronomical observations might provide us with valuable information on the equation of state of hot dense matter.

We calculate the momentum given to a proto-neutron star during the first 10 s after temperature equilibrium is reached, using recent evidence of sterile neutrinos and a measurement of the mixing angle. This is a continuation of an earlier estimate with a wide range of possible mixing angles. Using the new mixing angle we find that sterile neutrinos can account for the observed pulsar velocities.

In this paper the formulae of magnetic susceptibility (MS) of charged particles are deduced in nonrelativistic and relativistic mean-field approximations in bulk matter. The analytic relativistic expression at high densities and strong fields, deduced for the de Hass–van Alphen (HVA) oscillation, shows that the oscillation frequency is proportional to the square of chemical potential and the reciprocal of the field, and is independent of the temperature. Numerical calculations are performed at finite temperatures and in a field range where the equation of state is not sensitive to the field. The nonoscillatory MS of the protoneutron star, which is dominated by the contributions of electrons (and light quarks, if deconfined) and is almost independent of the field, decreases as the protoneutron matter becomes denser. The numerical results for the HVA oscillation are also given. The oscillation amplitude becomes larger as the star becomes colder. We find that superposition of the HVA oscillations changes the oscillation properties drastically if the color deconfinement occurs at high densities.

The decreasing of the inertial mass density, established in the past for dissipative fluids, is found to be produced by the "inertial" term of the transport equation. Once the transport equation is coupled to the dynamical equation, one finds that the contribution of the inertial term diminishes the effective inertial mass and the "gravitational" force term, by the same factor. An intuitive picture and prospective applications of this result to astrophysical scenarios are discussed.

Although there is a general understanding of the core collapse supernovae, a definitive microscopic model is still to come. We discuss the usefulness of neutrino observations. We analyze the SN1987A observations of Kamiokande-II, IMB and Baksan and show that they provide a 2.5σ support to the standard scenario for the explosion. In this context, we discuss the neutrinos as trigger for the search of the gravity wave impulsive emission. We bound the neutrino mass using the SN1987A data and argue, using simulated data, that a future galactic supernova could probe the sub-eV region.

We review recent progress in our understanding of the nature of Gamma Ray Bursts (GRBs) and in particular, of the relationship between short GRBs and long GRBs. The first example of a short GRB is described. The coincidental occurrence of a GRB with a supernova (SN) is explained within the induced gravitational collapse (IGC) paradigm, following the sequence: (1) an initial binary system consists of a compact carbon–oxygen (CO) core star and a neutron star (NS); (2) the CO core explodes as a SN, and part of the SN ejecta accretes onto the NS which reaches its critical mass and collapses to a black hole (BH) giving rise to a GRB; (3) a new NS is generated by the SN as a remnant. The observational consequences of this scenario are outlined.

Motivated by the success of kinetic theory in the description of observables in intermediate and high energy heavy-ion collisions, we apply kinetic theory to the physics of supernova explosions. The algorithmic implementation for the high-density phase of the iron core collapse is discussed.

The evolution of the baryon distribution in different phases, derived from cosmological simulations, are here reported. These computations indicate that presently most of baryons are in a warm-hot intergalactic (WHIM) medium (about 43%) while at z = 2.5 most of baryons constitute the diffuse medium (about 74%). Stars and the cold gas in galaxies represent only 14% of the baryons at z = 0. For z < 4 about a half of the metals are locked into stars while the fraction present in the WHIM and in the diffuse medium increases with a decreasing redshift. In the redshift range 0 ≤ z ≤ 2.5, the amount of metals in the WHIM increases from 4% to 22% while in the diffuse medium it increases from 0.6% to 4%. This enrichment process is due essentially to a turbulent diffusion mechanism associated to mass motions driven by supernova explosions. At z = 0, simulated blue (late type) galaxies show a correlation of the oxygen abundance present in the cold gas with the luminosity of the considered galaxy that agrees quite well with data derived from HII regions.

A possible mechanism for the formation of heavy-mass elements in supernovae is the rapid neutron-capture-mechanism ($r$-process). It depends upon the electron-fraction $Y_e$, a quantity which is determined by beta-decay-rates. In this paper, we focus on the calculation of electroweak decay-rates in presence of massive neutrinos. The resulting expressions are then used to calculate nuclear reactions entering the rapid-neutron capture. We fix the astrophysical parameters to the case of a core-collapse supernova. The neutrino sector includes a mass scheme and mixing angles for active neutrinos, and also by including the mixing between active and sterile neutrinos. The results of the calculations show that the predicted abundances of heavy-mass nuclei are indeed affected by the neutrino mixing.

We consider in this paper a simple oscillating Quintom model of dark energy which has two free parameters and an equation of state oscillating and crossing -1. For low redshifts the equation of state of this model resembles itself similar to the linearly parametrized dark energy, however differs substantially at large redshifts. We fit our model to the observational data separately from the new high redshifts supernova observations from the HST/GOODS program and previous supernova, CMB and galaxy clustering. Our results show that because of the oscillating feature of our model the constraints from observations at large redshifts such as CMB become less stringent.

Strong magnetic fields are suspected to exist in some core-collapse supernovae, which would affect the neutrino processes such as ν_e+n ⇌ e^-+p and . We briefly review the motion of charged particles in the presence of magnetic fields and the changes of the above processes induced by magnetic fields. We also discuss the implications of these changes for supernova physics in the context of neutrino-driven explosion.

We investigate the momentum given to a protoneutron star, the pulsar kick, during the first ten seconds after temperature equilibrium is reached. Using a model with two sterile neutrinos obtained by fits to the MiniBooNE and LSND experiments, which is consistent with a new global fit, there is a large mixing angle, and the effective volume for emission is calculated. Using formulations with neutrinos created by URCA processes in a strong magnetic field, so the lowest Landau level has a sizable probability, we find that with known parameters, the asymmetric sterile neutrino emissivity might account for large pulsar kicks.