Supernova
A supernova is an extraordinarily energetic stellar explosion that marks the catastrophic death of certain types of stars, releasing in seconds as much energy (roughly 10⁴⁴ J) as the Sun will radiate over its entire 10-billion-year lifetime, and briefly outshining an entire galaxy. Type Ia supernovae occur when a white dwarf in a binary system accretes enough mass to exceed the Chandrasekhar limit (~1.4 M☉), triggering runaway nuclear fusion; Type II supernovae occur when the iron core of a massive star (>8 M☉) collapses under gravity, producing a shockwave that ejects the outer layers. Supernovae are the primary source of elements heavier than iron in the universe and are used as "standard candles" in cosmology to measure vast intergalactic distances.
Key Formula
Total energy ≈ 3×10⁴⁶ J; Kinetic energy of ejecta ≈ 10⁴⁴ J; Neutrino energy ≈ 3×10⁴⁶ J
LaTeX: E_{\text{total}} \approx 3 \times 10^{46}\,\text{J},\quad E_{\text{kinetic}} \approx 10^{44}\,\text{J},\quad E_{\nu} \approx 3 \times 10^{46}\,\text{J}
| Symbol | Meaning | Unit |
|---|---|---|
| E_total | Total energy released in core collapse | J |
| E_kinetic | Kinetic energy of the ejected envelope | J |
| E_ν | Energy carried away by neutrinos (~99%) | J |
Classification and Properties of Supernova Types
| Type | Progenitor | Hydrogen Lines | Peak Luminosity (L☉) | Remnant |
|---|---|---|---|---|
| Type Ia | White dwarf exceeds Chandrasekhar limit | Absent | ~5×10⁹ | No compact remnant |
| Type Ib | Stripped massive star (Wolf-Rayet) | Absent | ~10⁸–10⁹ | Neutron star or black hole |
| Type Ic | Stripped massive star (no He shell) | Absent | ~10⁸–10⁹ | Neutron star or black hole |
| Type II-P | Red supergiant (>8 M☉) | Present | ~10⁸–10⁹ | Neutron star or black hole |
| Type II-L | Massive star (less H envelope) | Present | ~10⁸–10⁹ | Neutron star or black hole |
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Related Terms
Neutron Star
A neutron star is an extraordinarily dense stellar remnant formed when the core of a massive star (8–20 M☉) collapses during a Type II supernova, compressing a mass of 1.2–2.1 M☉ into a sphere only ~10–13 km in radius, resulting in densities comparable to atomic nuclei (~10¹⁴ g/cm³). The star is supported against further gravitational collapse by neutron degeneracy pressure—a quantum mechanical effect arising from the Pauli exclusion principle—rather than thermal or radiation pressure. Neutron stars often manifest as rapidly rotating pulsars, emitting beams of electromagnetic radiation from their magnetic poles at highly regular intervals, and they are key sources of gravitational waves when in binary systems.
Stellar Nuclear Fusion
Stellar nuclear fusion is the thermonuclear process occurring in a star's core whereby lighter atomic nuclei are forced together under extreme temperature and pressure to form heavier nuclei, releasing enormous amounts of energy according to Einstein's mass–energy equivalence. In main-sequence stars like the Sun, the dominant process is the proton–proton (pp) chain, which converts hydrogen into helium; more massive stars rely on the CNO (carbon–nitrogen–oxygen) cycle. This energy release provides the radiation pressure that counteracts gravitational collapse, maintaining a star's long-term equilibrium known as hydrostatic balance.
White Dwarf
A white dwarf is the dense, compact stellar remnant left behind after a low-to-intermediate mass star (0.5–8 M☉) has shed its outer layers as a planetary nebula, leaving an Earth-sized sphere of electron-degenerate matter composed primarily of carbon and oxygen at densities of ~10⁶ g/cm³. Unlike main sequence stars, white dwarfs are not powered by nuclear fusion; they simply radiate their residual thermal energy, cooling over billions to trillions of years from initially blue-white temperatures through yellow and orange to the theoretical endpoint of a cold, dark "black dwarf". The maximum mass a white dwarf can have before collapsing is the Chandrasekhar limit of ~1.4 M☉.
The term "supernova" was coined by Swiss-American astronomer Fritz Zwicky and German-American Walter Baade in 1931, combining Latin "super" (above, beyond) with "nova" (new), itself from Latin "nova stella" (new star), to distinguish these catastrophic explosions from ordinary novae, which are far less energetic.