Supernova neutrinos
[1] A massive star collapses at the end of its life, emitting on the order of 1058 neutrinos and antineutrinos in all lepton flavors.
[3] They carry away about 99% of the gravitational energy of the dying star as a burst lasting tens of seconds.
[6] Supernovae[a] are considered the strongest and most frequent source of cosmic neutrinos in the MeV energy range.
Since neutrinos are generated in the core of a supernova, they play a crucial role in the star's collapse and explosion.
[1] Therefore, observation of neutrinos from supernovae provides detailed information about core collapse and the explosion mechanism.
[8] Further, neutrinos undergoing collective flavor conversions in a supernova's dense interior offers opportunities to study neutrino-neutrino interactions.
[b] Nevertheless, with current detector sensitivities, it is expected that thousands of neutrino events from a galactic core-collapse supernova would be observed.
[14] Stirling A. Colgate and Richard H. White,[16] and independently W. David Arnett,[17] identified the role of neutrinos in core collapse, which resulted in the subsequent development of the theory of supernova explosion mechanism.
The Nobel Prize-winning event,[6] known as SN 1987A, was the collapse of a blue supergiant star Sanduleak -69° 202, in the Large Magellanic Cloud outside our Galaxy, 51 kpc away.
[19] Two kiloton-scale water Cherenkov detectors, Kamiokande II and IMB, along with a smaller Baksan Observatory, detected a total of 25 neutrino-events[19] over a period of about 13 seconds.
[24] The core-collapse events are the strongest and most frequent source of cosmic neutrinos in the MeV energy range.
[27] Supernova neutrinos are produced when a massive star collapses at the end of its life, ejecting its outer mantle in an explosion.
[6] Wilson's delayed neutrino explosion mechanism has been used for 30 years to explain core collapse supernova.
[1] Near the end of life, a massive star is made up of onion-layered shells of elements with an iron core.
During the early stage of the collapse, electron neutrinos are created through electron-capture on protons bound inside iron-nuclei:[15]
Hence, the electron degeneracy pressure is unable to stabilize the stellar core against the gravitational force, and the star collapses.
[1] The weakening of the shock wave results in mass infall, which forms a neutron star.
[15] The knowledge of flux and flavor content of the neutrinos behind the shock wave is essential to implement the neutrino-driven heating mechanism in computer simulations of supernova explosions.
This assumption is known as single angle approximation, which along with spherical symmetricity of the supernova, allows us to treat neutrinos emitted in the same flavor as an ensemble and describe their evolution only as a function of distance.
It produces a cone of Cherenkov light, which is detected by photomultiplier tubes (PMT's) arrayed on the walls of the detector.
[36] With current detector sensitivities, it is expected that thousands of neutrino events from a galactic core-collapse supernova would be observed.
[b] There have not been any galactic supernova in the Milky Way in the last 120 years,[38] despite the expected rate of 0.8-3 per century.
[39] Nevertheless, a supernova at 10 kPc distance will enable a detailed study of the neutrino signal, providing unique physics insights.
[13] Additionally, the next generation of underground experiments, like Hyper-Kamiokande, are designed to be sensitive to neutrinos from supernova explosions as far as Andromeda or beyond.
[3] Due to their weakly interacting nature, the neutrino signals from a galactic supernova can give information about the physical conditions at the center of core collapse, which would be otherwise inaccessible.
[8] Due to their weakly interacting nature, near light speed neutrinos emerge promptly after the collapse.
Therefore, a supernova will be observed in neutrino observatories before the optical signal, even after travelling millions of light years.
The coincident detection of neutrino signals from different experiments would provide an early alarm to astronomers to direct telescopes to the right part of the sky to capture the supernova's light.
[14] The flavor evolution of neutrinos, propagating through the dense and turbulent interior of the supernova, is dominated by the collective behavior associated with neutrino-neutrino interactions.
[40] Further, they can act as a standard candle to measure cosmic distance as the neutronization burst signal does not depend on its progenitor.
