Neutrinos from core-collapse supernovae

Abstract

The core of a massive star (M > 8 Msun) eventually collapses. This implosion usually triggers a supernova (SN) explosion that ejects most of the stellar envelope and leaves behind a neutron star (NS) with a mass of up to about 2 Msun. Sometimes the explosion fails and a black hole forms instead. The NS radiates its immense binding energy (some 10% of its rest mass or $2-4\times10^{53}$ erg) almost entirely as neutrinos and antineutrinos of all flavors with typical energies of some 10 MeV. This makes core-collapse SNe the most powerful neutrino factories in the Universe. Such a signal was observed once - with limited statistics - from SN 1987A in the Large Magellanic Cloud. Today, however, many large neutrino detectors act as SN observatories and would register a high-statistics signal. A future Galactic SN, though rare (1-3 per century), would produce a wealth of astrophysical and particle-physics information, including possible signatures for new particles. Neutrinos are key to SN dynamics in the framework of the Bethe-Wilson delayed explosion paradigm. After collapse, they are trapped in the core for a few seconds, forming a dense neutrino plasma that can exhibit collective flavor evolution caused by the weak interaction, a subject of intense theoretical research.

Figures (15)

• Figure 1: Historical supernova of 1054 that has produced the Crab Nebula (left) and a compact remnant, the Crab Pulsar (right), a pulsating neutron star, near the center of the nebula. The gravitational and nuclear binding energy of the neutron star, some 10% of its rest mass, is emitted as a neutrino burst that lasts for a few seconds and drives the explosion. Such a burst was observed only once (from the historical SN 1987A on 23 February 1987). A future nearby supernova could be seen with high statistics in many active neutrino detectors and possibly in gravitational waves. The Crab Nebula image was taken by the Hubble Space Telescope (credit https://hubblesite.org/contents/media/images/3885-Image). The main pulsar image was taken in X-rays by the Chandra satellite, superimposed with an optical (HST) and infrared (Spitzer) image (credit https://chandra.harvard.edu/photo/2018/crab/).
• Figure 2: Core collapse and subsequent supernova (SN) explosion of a massive star ($M\gtrsim 8\,M_\odot$) as described in the text. The collapsed SN core, forming a proto-neutron star, is so dense and hot that the thermal neutrinos are trapped and carry away the gravitational binding energy of $2$--$4\times10^{53}~{\rm erg}$ of the final neutron star over a period of several seconds.
• Figure 3: Schematic picture of the core collapse of a massive star ($M\gtrsim 8\,M_\odot$), of the formation of a neutron-star (NS) remnant, and the beginning of a supernova (SN) explosion. There are four main phases numbered 1--4 above the plot: (1) Collapse. (2) Prompt-shock propagation and break-out through the neutrino sphere, release of prompt $\nu_e$ burst. (3) Matter accretion and mantle cooling. (4) Kelvin-Helmholtz cooling of proto-neutron star (PNS). The curves mark the evolution of several characteristic radii: The stellar iron core ($R_{\rm Fe}$). The neutrino sphere ($R_\nu$) with diffusive transport inside, free streaming outside. The inner core ($R_{\rm ic}$), which for $t\lesssim 0.1~{\rm s}$ is the region of subsonic collapse, later it is the settled, compact inner region of the nascent neutron star. The SN shock wave ($R_{\rm shock}$) is formed at core bounce, stagnates for up to several $100~{\rm ms}$, and is revived by neutrino heating---it then propagates outward and ejects the stellar envelope. The shaded area is where most of the neutrino emission comes from; between this area and $R_\nu$, neutrinos still diffuse, but are no longer efficiently produced. (Adapted from Raffelt:1996wa, © University of Chicago Press. Figure originally adapted from Janka Janka:1992jk.)
• Figure 4: Three-dimensional simulation by the Garching group of a $19\,M_\odot$ progenitor Bollig:2020phc. Up to the vertical line, the postbounce (pb) time axis is linear, beyond it is logarithmic, and up to that break, neutrino transport was done with the Vertex code, whereas for the long-term evolution, a numerically cheaper heating and cooling scheme was applied. Left. Mass shells (black lines) and entropy per nucleon color-coded. Maximum, minimum, and average shock radii as white lines, the gain radius is the lowest white line, and in red, the mass shells of Si/O shell interface and final neutron-star mass boundary. Right. Neutrino luminosities and mean energies of $\nu_e$, $\overline\nu_e$, and one species $\nu_x$ of heavy-lepton neutrinos $\nu_\mu$, $\overline\nu_\mu$, $\nu_\tau$, or $\overline\nu_\tau$. (Figure from Bollig:2020phc with permission of the AAS.)
• Figure 5: Profile of the Garching muonic SN model SFHo-18.8 at $t_{\rm pb}=1\,{\rm s}$Bollig:2020xdrCaputo:2021rux. Top. Chemical potentials, temperature, plasma frequency $\omega_{\rm p}$, and Debye screening scale $k_{\rm s}$. Bottom. Number densities $n_i$, normalized to $n_0 = 0.181~{\rm fm}^{-3}$, corresponding to nuclear density of $3\times10^{14}~{\rm g}~{\rm cm}^{-3}$. (Figure from Ref. Caputo:2021rux, © 2022 American Physical Society.)