Physics with Supernovae

Core-collapse supernovae (SNe) are powerful neutrino sources and as such important targets for the growing array of neutrino observatories. We review the current status of SN theory and the expected characteristics of the neutrino signal. After recalling what we have learned from SN 1987A and general SN properties we review the physics potential of a future galactic SN observation. Supernovae are exploding stars [1–5]. However , there are two entirely different classes, both of which are of current interest for astro-particle physics and cosmology. One physical class are the type Ia supernova (SN) explosions. A SN Ia is thought to occur when a carbon-oxygen white dwarf accretes matter from a companion star until it reaches its Chandrasekhar limit and begins to collapse, thereby triggering a nuclear explosion , powered by the fusion of carbon and oxygen to heavier nuclei. SNe Ia are spectroscopically characterized by the absence of hydrogen and the presence of silicon lines. The explosion disrupts the progenitor white dwarf entirely; what remains is an expanding nebula without a central compact object. While the exact SN Ia lightcurves depend on some parameters, they are surprisingly reproducible and thus lend themselves as cosmo-logical standard candles. The main astro-particle interest in SNe Ia is their potential to explore the space-time geometry of the universe; the observed SN Ia Hubble diagram suggests the presence of " dark energy " or a cosmological constant [6,7]. The present lecture is exclusively about the other class of explosions which mark the evolutionary end of massive stars (M > ∼ 8 M ⊙). Such stars have the usual onion structure with several burning shells, an expanded envelope, and a degenerate iron core that is essentially an iron white dwarf. The core mass grows by the nuclear burning at its edge until it reaches the Chandrasekhar limit. The collapse can not ignite nuclear fusion because iron is the most tightly bound nucleus. Therefore, the collapse continues until the equation of state stiffens by nucleon degeneracy pressure at about nuclear density (3 × 10 14 g cm −3). At this " bounce " a shock wave forms, moving outward and expelling the stellar mantle and envelope. The explosion is a reversed implosion, the energy derives from gravity, not from nuclear energy. Within the expanding nebula, a compact object remains in the form of a neutron star or perhaps sometimes a black hole. The kinetic energy of the …