Supernova

A supernova is a luminous stellar explosion produced by thermonuclear disruption or the collapse of a stellar core.

A hypothetical explosion in which a degenerate carbon-oxygen core within a single evolved star grows toward the Chandrasekhar mass and ignites explosive carbon burning while retaining an envelope. This differs from accretion onto an already exposed white dwarf in standard Type Ia supernova scenarios. Evolutionary calculations by Doherty et al. explain the strong dependence of this proposed channel on envelope mass loss; their adopted winds remove the carbon-oxygen envelope before this outcome. It is a proposed possibility under different assumptions, rather than an established endpoint for normal $5M_{\odot }$ stars.

Collapse of a massive stellar core can launch an explosion that ejects material processed by hydrostatic and explosive burning. Whether an explosion succeeds, and how much material escapes instead of falling back, depend on the core and envelope structure. A failed supernova can retain much of the nucleosynthetic core; initial stellar mass alone is not a complete prediction.

SN 1987A supplied a prompt terrestrial record of neutrino emission from a core-collapse supernova through its SN 1987A neutrino burst.^[ref]

The original Kamiokande paper reported a low-energy event cluster on 23 February 1987 above surrounding background. Inverse beta decay, ${\bar{\nu }}_e+p⟶e^{+}+n$, provides an electron antineutrino channel through Positron light. Neutrino-Electron elastic scattering is more directional. The burst supported core-collapse supernova neutrino emission, with limited statistics and channel ambiguity.^[ref]

An original counting illustration shows why timing matters. Suppose an independently measured background is a Poisson process of rate $b$. In a prespecified window $\Delta t$, the probability of at least two background events isFor the synthetic choice $b\Delta t=0.1$, this is about $0.004679$, obtained by subtracting the zero- and one-event probabilities of the Poisson distribution. The Homestake experiment's delayed extraction cannot supply such capture-time clustering. This calculation is not a significance estimate for SN 1987A: searching many possible windows, varying acceptance and correlated backgrounds change the inference.

Core collapse can fail to produce an ordinary successful ejecting supernova, leaving a black hole and retaining much of the processed core. Some envelope material can still escape, depending on the event; failure is not equivalent to a universal zero-yield prescription.

In a hot radiation-supported stellar core, electron-positron thermal pair abundance can grow as radiation energy is converted into pair rest energy. The stellar adiabatic exponent can fall below $4/3$, permitting contraction and rapid heating. If the resulting explosive nuclear fusion releases enough energy, it disrupts the star in a pair-instability supernova. Weaker events can produce pulses rather than full disruption, and still heavier cores can collapse without an explosion. Thus the thermal relativity scale alone neither establishes the instability nor predicts its outcome.

A Type Ia supernova is a thermonuclear supernova whose standardized luminosity makes it a useful astronomical distance indicator.

The nickel-56 to cobalt-56 to iron-56 decay chain supplies gamma rays and charged particles that heat supernova ejecta. Early expansion and photon diffusion delay the escaping optical light; after a peak on a scale of weeks, the luminosity falls as decay power declines and gamma rays escape more readily. With comparable diffusion times and deposition efficiencies, peak luminosity scales approximately with the nickel-56 mass. Using one fixed absolute luminosity without accounting for composition-dependent yields can therefore bias standard-candle distances.

Approximate a fixed mass of iron-group freeze-out ashes by nickel-56 and iron-54, with no further weak neutronization and negligible residual light particles. Their electron fractions are $1/2$ and $26/54$. Conservation of the initial electron fraction in stellar matter, $1/2-X_{22}/22$, then gives the displayed nickel mass fraction. Its argument is the initial neon-22 mass fraction, which need not equal the earlier nitrogen metallicity. The two-isotope mass-budget approximation is not an exact full nuclear equilibrium with all free-particle densities set to zero.