arXiv subjects

Koh Takahashi

Publications and source records attributed to Koh Takahashi.

At least 19 recordsLinked to original sources

arXiv2026

Chemical Abundance Ratios of Nitrogen Rich Galaxies Identified at $z\sim 6-12$: Observational Demographics and Models

We present chemical abundance ratios of 8 nitrogen-rich ([N/O]$>0.3$) galaxies at $z\sim 6-12$ identified by the first 4 years of the JWST observations, and compare these ratios with chemical evolution models. We reanalyze the JWST/NIRSpec data of these galaxies in the self-consistent manner for line fluxes and upper limits including those previously unconstrained. We derive the abundance ratios and constraints of [N/O], [C/O], [Ne/O], [Ne/C], [Ar/O], [S/O] and [Fe/O], characterizing the nebulae in the galaxies with the electron temperatures and densities measured with {\sc[Oiii]}$\lambda4363$ and {\sc[Oii]}$λ\lambda3727, 3729$ lines, respectively. We develop the chemical evolution models for the three major scenarios, Wolf-Rayet stars, supermassive stars, and tidal disruption events (TDEs) with the AGB star contribution, integrating the ejecta of the stars and core-collapse supernovae (CCSNe) over the age with yields calculated by numerical simulations. We compare the models with the [N/O] measurements and stellar ages, and find that all of the scenarios reproduce [N/O] as high as those of our galaxies. However, the time-scales of the high [N/O] ratios are too short to explain our galaxies in any of the scenarios, suggestive of very frequent failed supernovae that do not increase oxygen against nitrogen. We find that the three scenarios are distinguished in the plane of [Ne/C] vs. [N/O] due to Ne production outside CNO cycle, and that the observed abundance ratios are explained by the Wolf-Rayet models better than supermassive-star and TDE models. We argue that abundance ratios of various elements and time scales are clues for understanding nitrogen-rich galaxies.

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arXiv2026

The Impact of the New $^{59}$Fe Decay Rates on $^{60}$Fe and $^{26}$Al Nucleosynthesis in Massive Stars

The diffuse $γ$-ray emission from short-lived radioactive $^{26}$Al and $^{60}$Fe provides a direct probe of ongoing nucleosynthesis in the Galaxy. However, theoretical models have long struggled to reproduce the observed $^{60}$Fe/$^{26}$Al flux ratio, typically predicting values significantly higher than constraints derived from INTEGRAL/SPI observations. In this work, we investigate the impact of the recently measured, temperature-dependent stellar $β^-$ decay rate of $^{59}$Fe on the nucleosynthesis of these isotopes. We compute a grid of non-rotating massive star models ($14$-$80$ M$_\odot$) at solar metallicity using the MESA code, coupled with a rigorous numerical resolution analysis. We find that the updated rate significantly suppresses the net production of $^{60}$Fe by approximately 0.28 dex ($\sim 47\%$) compared to models using LMP theoretical rates, while leaving $^{26}$Al yields virtually unchanged. This reduction is primarily driven by the enhanced $β^-$ decay during convective carbon shell burning. Integrating these yields over a standard Salpeter Initial Mass Function, we predict a Galactic flux ratio of $\sim 0.18$, which is in excellent agreement with the observed value of $0.184 \pm 0.042$. Furthermore, this ratio exhibits a weak dependence on the IMF slope. Our results indicate that the updated nuclear physics input significantly alleviates the long-standing $^{60}$Fe overproduction problem, bringing theoretical predictions into much closer alignment with current Galactic observations.

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arXiv2026

Comparing explodability predictions from a parameter-optimized semi-analytic model with structure-based progenitor criteria

Three-dimensional (3D) simulations of neutrino-driven core-collapse supernovae are among the most reliable tools for predicting explosion outcome. However, their high computational cost limits systematic surveys over large progenitor samples. We test how well a fast one-dimensional (1D) approach captures progenitor explodability. We use a parameter-optimized semi-analytic 1D explosion model based on Müller et al. (2016), calibrated to the 3D results of Burrows et al. (2024) as an adopted reference set. We compare the model's explodability predictions with commonly used structure-based criteria: compactness, the free-fall mass coordinate, and the two-parameter $μ_4$-$M_4$ criterion. Our analysis shows that the semi-analytic model can reproduce the trends seen in this adopted 3D calibration set by adjusting physically meaningful parameters. This provides a more direct way to examine the physics that controls explodability than traditional structure-based criteria. We identify where the semi-analytic model agrees with these criteria, where it differs, and which physical trends explain the differences. This work clarifies the strengths and limitations of structure-based explodability criteria by evaluating them against a parameter-optimized, neutrino-driven semi-analytic model.

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arXiv2025

Fe Abundances of Early Galaxies at $z=9-12$ Derived with Deep JWST Spectra

We derive Fe-abundance ratios of 7 galaxies at $z=9-12$ with $-22<M_{\mathrm{UV}}<-19$ whose JWST/NIRSpec spectra achieve very high signal-to-noise ratios, $\mathrm{SNR}=60-320$, at the rest-frame UV wavelength. We fit stellar population synthesis model spectra to these JWST spectra, masking out nebular emission lines, and obtain Fe-abundance ratios of $\mathrm{[Fe/H]}=-1-0$ dex for 5 galaxies and upper limits of $\mathrm{[Fe/H]}\sim-2-0$ dex for 2 galaxies. We compare these [Fe/H] values with the oxygen abundances of these galaxies ($7.4<12+\log{\mathrm{(O/H)}}<8.4$) in the same manner as previous studies of $z\sim2-6$ galaxies, and derive oxygen-to-iron abundance ratios [O/Fe]. We find that 2 out of 7 galaxies, GS-z11-0 and GN-z11, show Fe enhancements relative to O ($\mathrm{[O/Fe]}<0$ dex), especially GS-z11-0 ($z=11.12$) with a Fe enhancement ($\mathrm{[O/Fe]}=-0.68_{-0.55}^{+0.37}$ dex) beyond the solar-abundance ratio at $\sim2σ$. Because, unlike GS-z11-0, GN-z11 ($z=10.60$) may be an AGN, we constrain [O/Fe] via FeII emission under the assumption of AGN and confirm that the Fe enhancement is consistent even in the case of AGN. While [O/Fe] values of most galaxies are comparable to those of core-collapse supernovae (CCSNe) yields, the Fe enhancements of GS-z11-0 and GN-z11 are puzzling. We develop chemical evolution models, and find that the Fe enhancements in GS-z11-0 and GN-z11 can be explained by 1) pair-instability supernovae/bright hypernovae with little contribution of CCSNe or 2) Type-Ia supernovae with short delay time ($\sim30-50$ Myr) with a top-light initial mass function.

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arXiv2025

Inhomogeneous stellar mixing in the final hours before the Cassiopeia A supernova

Understanding stars and their evolution is a key goal of astronomical research and has long been a focus of human interest. In recent years, theorists have paid much attention to the final interior processes within massive stars, as they can be essential for revealing neutrino-driven supernova mechanisms and other potential transients of massive star collapse. However, it is challenging to observe directly the last hours of a massive star before explosion, since it is the supernova event that triggers the start of intense observational study. Here we report evidence for a final phase of stellar activity known as a ``shell merger'', an intense shell burning in which the O-burning shell swallows its outer C-/Ne-burning shell, deep within the progenitor's interior moments before the supernova explosion. In the violent convective layer created by the shell merger, Ne, which is abundant in the stellar O-rich layer, is burned as it is pulled inward, and Si, which is synthesized inside, is transported outward. The remnant still preserves some traces of such Ne-rich downflows and Si-rich upflows in the O-rich layer, suggesting that inhomogeneous shell-merger mixing began just hours ($\lesssim 10^4$ s) before its gravitational collapse. Our results provide the first observational evidence that the final stellar burning process rapidly alters the internal structure, leaving a pre-supernova asymmetry. This breaking of spherical symmetry facilitates the explosion of massive stars and influences various supernova and remnant characteristics, including explosion asymmetries and the neutron star's kick and spin.

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arXiv2024

Variety of disc wind-driven explosions in massive rotating stars. II. Dependence on the progenitor

We assess the variance of supernova(SN)-like explosions associated with the core collapse of rotating massive stars into a black hole-accretion disc system under changes in the progenitor structure. Our model of the central engine evolves the black hole and the disc through the transfer of matter and angular momentum and includes the contribution of the disc wind. We perform two-dimensional, non-relativistic, hydrodynamics simulations using the open-source hydrodynamic code Athena++, for which we develop a method to calculate self-gravity for axially symmetric density distributions. For a fixed model of the wind injection, we explore the explosion characteristics for progenitors with zero-age main-sequence masses from 9 to 40 $M_\odot$ and different degrees of rotation. Our outcomes reveal a wide range of explosion energies with $E_\mathrm{expl}$ spanning from $\sim 0.3\times10^{51}$~erg to $ > 8\times 10^{51}$~erg and ejecta mass $M_\mathrm{ej}$ from $\sim 0.6$ to $> 10 M_\odot$. Our results are in agreement with some range of the observational data of stripped-envelope and high-energy SNe such as broad-lined type Ic SNe, but we measure a stronger correlation between $E_\mathrm{expl}$ and $M_\mathrm{ej}$. We also provide an estimate of the $^{56}$Ni mass produced in our models which goes from $\sim0.04\;M_\odot$ to $\sim 1.3\;M_\odot$. The $^{56}$Ni mass shows a correlation with the mass and the angular velocity of the progenitor: more massive and faster rotating progenitors tend to produce a higher amount of $^{56}$Ni. Finally, we present a criterion that allows the selection of a potential collapsar progenitor from the observed explosion energy.

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arXiv2024

Standing torsional Alfvén waves as the source of the rotational period variation in magnetic early-type stars

Context. The influence of magnetic fields on stellar evolution remains unresolved. It has been proposed that if there is a large-scale magnetic field in the stellar interior, torsional waves could arise, efficiently transporting angular momentum. In fact, the observed variations in the rotation periods of some magnetic stars may be attributed to these torsional waves' standing waves. Aims. To demonstrate the existence of torsional waves through modeling of the rotational period variations. Method. We conduct an eigenmode analysis of standing waves based on one-dimensional magnetohydrodynamic equations. The internal magnetic field structures are parametrically represented to treat poloidal fields with different degrees of central/surface concentration. The obtained frequencies are compared with the observed frequencies of the rotational period variations, thereby constraining the internal magnetic field structures. Results. The 67.6 years exhibited by CU Vir is reproduced for surface-concentrated magnetic field structures. The rotational period variations of all ten magnetic stars analyzed in this study are inconsistent with a centrally concentrated magnetic field. Conclusions. Torsional waves can reproduce the observations of rotational period variations. The large-scale magnetic fields within magnetic stars would be concentrated on the surface.

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arXiv2024

Low [O/Fe] Ratio in a Luminous Galaxy at the Early Cosmic Epoch ($z>10$): Signature of Short Delay Time or Bright Hypernovae/Pair-Instability Supernovae?

We present an [O/Fe] ratio of a luminous galaxy GN-z11 at $z=10.60$ derived with the deep public JWST/NIRSpec data. We fit the medium-resolution grating (G140M, G235M, and G395M) data with the model spectra consisting of BPASS-stellar and CLOUDY-nebular spectra in the rest-frame UV wavelength ranges with Fe absorption lines, carefully masking out the other emission and absorption lines in the same manner as previous studies conducted for lower redshift ($z\sim 2-6$) galaxies with oxygen abundance measurements. We obtain an Fe-rich abundance ratio $\mathrm{[O/Fe]}=-0.37^{+0.43}_{-0.22}$, which is confirmed with the independent deep prism data as well as by the classic 1978 index method. This [O/Fe] measurement is lower than measured for star-forming galaxies at $z\sim 2-3$. Because $z=10.60$ is an early epoch after the Big Bang ($\sim 430$ Myr) and the first star formation (likely $\sim 200$ Myr), it is difficult to produce Fe by Type Ia supernovae (SNeIa) requiring sufficient delay time for white-dwarf formation and gas accretion. The Fe-rich abundance ratio in GN-z11 suggests that the delay time is short, or that the major Fe enrichment is not accomplished by SNeIa but bright hypernovae (BrHNe) and/or pair-instability supernovae (PISNe), where the yield models of BrHNe and PISNe explain Fe, Ne, and O abundance ratios of GN-z11. The [O/Fe] measurement is not too low to rule out the connection between GN-z11 and globular clusters (GCs) previously suggested by the nitrogen abundance, but rather supports the connection with a GC population at high [N/O] if a metal dilution process exists.

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arXiv2024

Strong He I Emission Lines in High N/O Galaxies at $z \sim 6$ Identified in JWST Spectra: High He/H Abundance Ratios or High Electron Densities?

We present HeI/H$β$-flux and He/H-abundance ratios in three JWST galaxies with significant constraints on N/O-abundance ratios, GS-NDG-9422, RXCJ2248-ID, and GLASS150008 at $z\sim 6$ mostly with the spectroscopic coverage from HeI$λ$4471 and HeII$λ$4686 to HeI$λ$7065, comparing with 68 local-dwarf galaxies. We find that these high-$z$ galaxies present strong HeI emission with HeI/H$β$ flux ratios generally larger than those of local-dwarf galaxies. We derive He/H with all of the detected HeI, HeII, and $2-3$ hydrogen Balmer lines in the same manner as the local He/H determination conducted for cosmology studies. These high-$z$ galaxies show He overabundance He/H$\gtrsim 0.10$ or high electron density $n_\mathrm{e}\sim 10^{3-4}$ cm$^{-3}$ much larger than local values at low O/H, $12+\log \mathrm{(O/H)}=7-8$. In contrast, we obtain low He/H and $n_\mathrm{e}$ values for our local-dwarf galaxies by the same technique with the same helium and hydrogen lines, and confirm that the difference between the high-$z$ and local-dwarf galaxies are not mimicked by systematics. While two scenarios of 1) He overabundance and 2) high electron density are not clearly concluded, we find that there is a positive correlation on the He/H-N/O or $n_\mathrm{e}$-N/O plane by the comparison of the high-$z$ and local-dwarf galaxies. The scenario 1) suggests that the overabundant helium and nitrogen are not explained by the standard chemical enrichment of core-collapse supernovae, but the CNO-cycle products and equilibrium ratios, respectively. The scenario 2) indicates that the strong helium lines are originated from the central dense clouds of the high-$z$ galaxies by excessive collisional excitation.

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arXiv2024

EMPRESS. XIII. Chemical Enrichments of Young Galaxies Near and Far at z ~ 0 and 4-10: Fe/O, Ar/O, S/O, and N/O Measurements with Chemical Evolution Model Comparisons

We present gas-phase elemental abundance ratios of 7 local extremely metal-poor galaxies (EMPGs) including our new Keck/LRIS spectroscopy determinations together with 33 JWST $z\sim 4-10$ star-forming galaxies in the literature, and compare chemical evolution models. We develop chemical evolution models with the yields of core-collapse supernovae (CCSNe), Type Ia supernovae, hypernovae (HNe), and pair-instability supernovae (PISNe), and compare the EMPGs and high-$z$ galaxies in conjunction with dust depletion contributions. We find that high Fe/O values of EMPGs can (cannot) be explained by PISN metal enrichments (CCSN/HN enrichments even with the mixing-and-fallback mechanism enhancing iron abundance), while that the observed Ar/O and S/O values are much smaller than the predictions of the PISN models. The abundance ratios of the EMPGs can be explained by the combination of Type Ia SNe and CCSNe/HNe whose inner layers of argon and sulfur mostly fallback, which are comparable with Sculptor stellar chemical abundance distribution, suggesting that early chemical enrichment is taken place in the EMPGs. Comparing our chemical evolution models with the star-forming galaxies at $z\sim 4-10$, we find that the Ar/O and S/O ratios of the high-$z$ galaxies are comparable with those of the CCSNe/HNe models, while majority of the high-$z$ galaxies do not have constraints good enough to rule out contributions from PISNe. The high N/O ratio recently reported in GN-z11 cannot be explained even by rotating PISNe, but could be reproduced by the winds of rotating Wolf Rayet stars that end up as a direct collapse.

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arXiv2024

Destratification in the Progenitor Interior of the Mg-rich Supernova Remnant N49B

Simulations of pre-supernova evolution suggest that some intense shell burning can be so active that, in extreme cases, it can merge with the outer shell, changing the initial conditions for the supernova explosion. However, such violent activity in the interior of stars has been difficult to confirm from observations of stars. Here we propose that the elemental composition of O-rich ejecta in supernova remnants can be a tool to test for this kind of intense shell burning activity in the final stages of progenitor evolution. As an example, we discuss the origin of "Mg-rich" ejecta in the supernova remnant N49B. A high Mg/Ne mass ratio $\gtrsim 1$ suggests that the Ne- or O-burning shell has broken into or merged with the outer shell before the collapse. Such Mg-rich (or Ne-poor) ejecta has been identified in some other supernova remnants, supporting the idea that some destratification process, such as a shell merger, does indeed occur in the interiors of some massive stars, although they may not be the majority. Our results suggest that X-ray observations of O-rich ejecta in core-collapse supernova remnants will be a unique tool to probe the shell burning activity during the final stage of a massive star's interior.

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arXiv2024

Variety of disk wind-driven explosions in massive rotating stars

We perform a set of two-dimensional, non-relativistic, hydrodynamics simulations for supernova-like explosion associated with stellar core collapse of rotating massive stars to a system of a black hole and a disk connected by the transfer of matter and angular momentum. Our model of the central engine also includes the contribution of the disk wind. In this work, we specifically investigate the wind-driven explosion of rotating, large-mass progenitor stars with the zero-age main-sequence mass of $M_\mathrm{ZAMS}=20\,M_\odot$ from arXiv:2008.09132 . This study is carried out using the open-source hydrodynamic code Athena++, for which we implement a method to calculate self-gravity for axially symmetric density distributions. We, then, investigate the explosion properties and the $^{56}$Ni production as a function of (varying) some features of the wind injection. We find a large variety of explosion energy with $E_\mathrm{expl}$ ranging from $\sim 0.049\times10^{51}$~erg to $\sim 34\times10^{51}$~erg and ejecta mass $M_\mathrm{ej}$ from 0.58 to 6 $M_\odot$, which shows a bimodal distribution in high- and low-energy branches. We demonstrate that the resulting outcome of a highly- or sub-energetic explosion for a certain stellar structure is mainly determined by the competition between the ram pressure of the injected matter and that of the infalling envelope. In the nucleosynthesis analysis the $^{56}$Ni mass produced in our models goes from $< 0.2~M_\odot$ in the sub-energetic explosions to $2.1~M_\odot$ in the highly-energetic ones. These results are consistent with the observational data of stripped-envelope and high-energy SNe such as broad-lined type Ic SNe. However, we find a tighter correlation between the explosion energy and the ejecta mass than that observationally measured.

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arXiv2024

Diagnosis of Circumstellar Matter Structure in Interaction-powered Supernovae with Hydrogen Line Feature

Some supernovae (SNe) are powered by collision of the SN ejecta with a dense circumstellar matter (CSM). Their emission spectra show characteristic line shapes of combined broad emission and narrow P-Cyg lines, which should closely relate to the CSM structure and the mass-loss mechanism that creates the dense CSM. We quantitatively investigate the relationship between the line shape and the CSM structure by Monte Carlo radiative transfer simulations, considering two representative cases of dense CSM formed by steady and eruptive mass loss. Comparing the H$α$ emission between the two cases, we find that a narrow P-Cyg line appears in the eruptive case while it does not appear in the steady case, due to the difference in the velocity gradient in the dense CSM. We also reproduce the blue-shifted photon excess observed in some Type IIn SNe, which is formed by photon transport across the shock wave and find the relationship between the velocity of the shocked matter and the amount of the blue shift of the photon excess. We conclude that the presence or absence of narrow P-Cyg lines can distinguish the mass loss mechanism, and suggest high-resolution spectroscopic observations with $λ/ Δλ\gtrsim 10^4$ after the light curve peak for applying this diagnostic method.

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arXiv2023

Evolution and explosions of metal enriched supermassive stars: proton rich general relativistic instability supernovae

The assembly of supermassive black holes poses a challenge primarily because of observed quasars at high redshift, but additionally because of the current lack of observations of intermediate mass black holes. One plausible scenario for creating supermassive black holes is direct collapse triggered by the merger of two gas rich galaxies. This scenario allows the creation of supermassive stars with solar metallicity, where the enhanced metallicity is enabled by extremely rapid accretion. We investigate the behavior of metal enriched supermassive stars which collapse due to the general relativistic radial instability during hydrogen burning. These stars contain both hydrogen and metals and thus may explode due to the CNO cycle (carbon-nitrogen-oxygen) and the rp process (rapid proton capture). We perform a suite of stellar evolution simulations for a range of masses and metallicities, both including and neglecting mass loss. We evaluate the stability of these supermassive stars by solving the pulsation equation in general relativity. When the stars becomes unstable, we perform 1D general relativistic hydrodynamical simulations coupled to a 153 isotope nuclear network with cooling from neutrino reactions, in order to determine if the stars explode. If the stars do explode, we post process the nucleosynthesis using a 514 isotope network which includes additional proton rich isotopes. These explosions are characterized by enhanced nitrogen and intermediate mass elements ($16\geq\rm{A}\geq25$), and suppressed light elements ($8\geq\rm{A}\geq14$), and we comment on recent observations of super-solar nitrogen in GN-z11.

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arXiv2023

Monotonicity of the cores of massive stars

Massive stars are linked with diverse astronomical processes and objects including star formation, supernovae and their remnants, cosmic rays, interstellar media, and galaxy evolution. Understanding their properties is of primary importance for modern astronomy, and finding simple rules that characterize them is especially useful. However, theoretical simulations have not yet realized such relations, instead finding that the late evolutionary phases are significantly affected by a complicated interplay between nuclear reactions, chemical mixing, and neutrino radiation, leading to non-monotonic initial mass dependencies of the iron core mass and the compactness parameter. We conduct a set of stellar evolution simulations, in which evolutions of He star models are followed until their central densities uniformly reach 10$^{10}$ g cm$^{-3}$, and analyze their final structures as well as their evolutionary properties including the lifetime, surface radius change, and presumable fates after core collapse. Based on the homogeneous data set, we have found that monotonicity is inherent in the cores of massive stars. We show that not only the density, entropy, and chemical distributions, but also their lifetimes and explosion properties such as the proto-neutron-star mass and the explosion energy can be simultaneously ordered into a monotonic sequence. This monotonicity can be regarded as an empirical principle that characterizes the cores of massive stars.

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arXiv2023

Pulsations of primordial supermassive stars induced by a general relativistic instability; visible to JWST at z$>$12

The origin of high-redshift quasars and their supermassive black hole engines is unclear. One promising solution is the collapse of a primordial supermassive star. Observational confirmation of this scenario may be challenging, but a general relativistic instability supernova provides one avenue for such. Previous studies have found that a general relativistic instability supernova has a potentially decades-long plateau phase visible to JWST at high redshift. In this work, we examine stars with mass just below the general relativistic instability supernova mass range. These stars pulsate, ejecting a portion of their envelopes. They then contract quasi-statically back to an equilibrium temperature, at which point they again become unstable and pulsate once more. Because each pulse consumes a small amount of the available nuclear fuel, there exists the possibility of multiple pulsations. We present simulations of the contracting phase, the pulsation, and the light-curve phase. We find that the lower mass pulsating models are even brighter than the higher mass supernovae because the pulsations occur in the late helium burning phase when the stars have extremely large radii. The fact that the pulsations are more luminous and occur in a wider mass range than the supernovae bodes well for observation.

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arXiv2022

Stability analysis of supermassive primordial stars: a new mass range for general relativistic instability supernovae

Observed supermassive black holes in the early universe have several proposed formation channels, in part because most of these channels are difficult to probe. One of the more promising channels, the direct collapse of a supermassive star, has several possible probes including the explosion of a helium-core supermassive star triggered by a general relativistic instability. We develop a straightforward method for evaluating the general relativistic radial instability without simplifying assumptions and apply it to population III supermassive stars taken from a post Newtonian stellar evolution code. This method is more accurate than previous determinations and it finds that the instability occurs earlier in the evolutionary life of the star. Using the results of the stability analysis, we perform 1D general relativistic hydrodynamical simulations and we find two general relativistic instability supernovae fueled by alpha capture reactions as well as several lower mass pulsations, analogous to the puslational pair instability process. The mass range for the events (2.6-3.0 $\times 10^4$ ${\rm M}_\odot$) is lower than had been suggested by previous works (5.5 $\times 10^4$ ${\rm M}_\odot$) because the instability occurs earlier in the star's evolution. The explosion may be visible to, among others, JWST, while the discovery of the pulsations opens up additional possibilities for observation.

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arXiv2022

Neutrino emission from the collapse of $\sim 10^4$ $M_\odot$ population III supermassive stars

We calculate the neutrino signal from Population III supermassive star collapse using a neutrino transfer code originally developed for core collapse supernovae and massive star collapse. Using this code, we are able to investigate the supermassive star mass range thought to undergo neutrino trapping ($\sim 10^4$ M$_\odot$), a mass range which has been neglected by previous works because of the difficulty of neutrino transfer. For models in this mass range, we observe a neutrino-sphere with a large radius and low density compared to typical massive star neutrino-spheres. We calculate the neutrino light-curve emitted from this neutrino-sphere. The resulting neutrino luminosity is significantly lower than the results of a previous analytical model. We briefly discuss the possibility of detecting a neutrino burst from a supermassive star or the neutrino background from many supermassive stars and conclude that the former is unlikely with current technology, unless the SMS collapse is located as close as 1 Mpc, while the latter is also unlikely even under very generous assumptions. However, the supermassive star neutrino background is still of interest as it may serve as a source of noise in proposed dark matter direct detection experiments.

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