Neutrino Emission From Stars


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Contact: F.X.Timmes
my one page vitae,
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research statement, and
teaching statement.
$ \def\Mzams{M_{\rm ZAMS}} \def\Msun\ensuremath{{\rm M}_\odot} \def\Lsun\ensuremath{{\rm L}_\odot} \def\Zsun\ensuremath{{\rm Z}_\odot} \def\Lnu\ensuremath{L_\nu} \def\Lgamma\ensuremath{L_\gamma} $ Stellar Neutrino Emission Across The Mass-Metallicity Plane (2023)

In this article we explore neutrino emission from nonrotating, single star models across six initial metallicities and seventy initial masses from the zero-age main sequence to the final fate. Overall, across the mass spectrum, we find metal-poor stellar models tend to have denser, hotter and more massive cores with lower envelope opacities, larger surface luminosities, and larger effective temperatures than their metal-rich counterparts. Across the mass-metallicity plane we identify the sequence (initial CNO $\rightarrow$ $^{14}$N $\rightarrow$ $^{22}$Ne $\rightarrow$ $^{25}$Mg $\rightarrow$ $^{26}$Al $\rightarrow$ $^{26}$Mg $\rightarrow$ $^{30}$P $\rightarrow$ $^{30}$Si) as making primary contributions to the neutrino luminosity at different phases of evolution. For the low-mass models we find neutrino emission from the nitrogen flash and thermal pulse phases of evolution depend strongly on the initial metallicity. For the high-mass models, neutrino emission at He-core ignition and He-shell burning depends strongly on the initial metallicity. Anti-neutrino emission during C, Ne, and O burning shows a strong metallicity dependence with $^{22}$Ne($\alpha$,$n$)$^{25}$Mg providing much of the neutron excess available for inverse-$\beta$ decays. We integrate the stellar tracks over an initial mass function and time to investigate the neutrino emission from a simple stellar population. We find average neutrino emission from simple stellar populations to be 0.5--1.2 MeV electron neutrinos. Lower metallicity stellar populations produce slightly larger neutrino luminosities and average $\beta$ decay energies. This study can provide targets for neutrino detectors from individual stars and stellar populations. We provide convenient fitting formulae and open access to the photon and neutrino tracks for more sophisticated population synthesis models.


Figure 1: Coverage in the mass-metallicity plane (center). The x-axis is the initial Z of a model relative to solar, and the y-axis is $\Mzams$ of a model relative to solar. Six metallicities, each marked with a different color, and 70 masses at each metallicity (circles) span the mass-metallicity plane. The nuclear reaction network for low-mass (left) and high-mass (right) models is illustrated. These x-axes are the difference in the number of neutrons and protons in an isotope. Positive values indicate neutron-rich isotopes, the zero value is marked by the red vertical line, and negative values indicate proton-rich isotopes. These y-axes are the number of protons in an isotope, labelled by their chemical element names. Isotopes in the reaction network are shown by purple squares. Reactions between isotopes are shown by gray lines. Note Fe in the low-mass reaction network does not react with other isotopes. Fe is included for a more consistent specification of the initial composition, hence any microphysics that depends upon the composition including the opacity, equation of state, element difffusion, and neutrino emission.


Figure 2: Light curves for photons (left) and neutrinos (right). Tracks span 0.2--150 $\Msun$ for Z=1 $\Zsun$ and are labeled. Key phases of evolution including the ZAMS (black circles), TAMS (black circles), core He flashes (light green), thermal pulses, and pre-supernova stage are also labeled. The PMS light curves are suppressed for visual clarity. $\Lnu$ during the nitrogen flash (He flash for photons) and thermal pulses for the M$<$8 $\Msun$ light curves can exceed $\Lgamma$. At and beyond core C-burning $\Lnu$ dominates the evolution of the M$\ge$8 $\Msun$ light curves. Luminosities are normalized to $\Lsun$ = 3.828 $\times$ 10$^{33}$ erg s$^{-1}$.


Figure 3: Total energy emitted in photons and neutrinos over the lifetime of a model (top) and their ratio (bottom) across the mass-metallicity plane. Transitions between different final fates occur at local extrema}, indicated by the colored panels and labels.

On Stellar Evolution In A Neutrino Hertzsprung-Russell Diagram (2020)

In this article we explore the evolution of a select grid of solar metallicity stellar models from their pre-main sequence phase to near their final fates in a neutrino Hertzsprung-Russell diagram, where the neutrino luminosity replaces the traditional photon luminosity.

Using a calibrated MESA solar model for the solar neutrino luminosity (L$_{\nu,\odot}$=0.02398 $\cdot$ L$_{\gamma,\odot}$=9.1795$\times$10$^{31}$ erg s$^{-1}$) as a normalization, we identify $\simeq$ 0.3 MeV electron neutrino emission from helium burning during the helium flash (peak L$_{\nu}$/L$_{\nu,\odot}$$\simeq$10$^4$, flux $\Phi_{\nu, {\rm He \ flash}} \simeq$ 170 (10 pc/$d$)$^{2}$ cm$^{-2}$ s$^{-1}$ for a star located at a distance of $d$ parsec, timescale $\simeq$ 3 days) and the thermal pulse (peak L$_{\nu}$/L$_{\nu,\odot}$$\simeq$10$^9$, flux $\Phi_{\nu, {\rm TP}}\simeq$1.7$\times$10$^7$ (10 pc/$d$)$^{2}$ cm$^{-2}$ s$^{-1}$, timescale $\simeq$ 0.1 yr) phases of evolution in low mass stars as potential probes for stellar neutrino astronomy.

We also delineate the contribution of neutrinos from nuclear reactions and thermal processes to the total neutrino loss along the stellar tracks in a neutrino Hertzsprung-Russell diagram. We find, broadly but with exceptions, that neutrinos from nuclear reactions dominate whenever hydrogen and helium burn, and that neutrinos from thermal processes dominate otherwise.

solar calibration - sound speed
solar calibration - mass density
photon and neutrino HR diagram
thermal vs. reaction neutrinos
photons vs. neutrino loses