Synoptic Sky Surveys and the Diffuse Supernova Neutrino Background: Removing Astrophysical Uncertainties and Revealing Invisible Supernovae

The cumulative (anti)neutrino production from all core-collapse supernovae within our cosmic horizon gives rise to the diffuse supernova neutrino background (DSNB), which is on the verge of detectability. The observed flux depends on supernova physics, but also on the cosmic history of supernova explosions; currently, the cosmic supernova rate introduces a substantial (+/-40%) uncertainty, largely through its absolute normalization. However, a new class of wide-field, repeated-scan (synoptic) optical sky surveys is coming online, and will map the sky in the time domain with unprecedented depth, completeness, and dynamic range. We show that these surveys will obtain the cosmic supernova rate by direct counting, in an unbiased way and with high statistics, and thus will allow for precise predictions of the DSNB. Upcoming sky surveys will substantially reduce the uncertainties in the DSNB source history to an anticipated +/-5% that is dominated by systematics, so that the observed high-energy flux thus will test supernova neutrino physics. The portion of the universe (z < 1) accessible to upcoming sky surveys includes the progenitors of a large fraction (~ 87%) of the expected 10-26 MeV DSNB event rate. We show that precision determination of the (optically detected) cosmic supernova history will also make the DSNB into a strong probe of an extra flux of neutrinos from optically invisible supernovae, which may be unseen either due to unexpected large dust obscuration in host galaxies, or because some core-collapse events proceed directly to black hole formation and fail to give an optical outburst.

💡 Research Summary

The paper addresses a long‑standing obstacle in predicting the diffuse supernova neutrino background (DSNB): the large (+/‑40 %) uncertainty in the cosmic core‑collapse supernova rate (CSNR). While the DSNB flux is fundamentally set by the neutrino emission physics of individual core‑collapse events, the integral over cosmic history requires an accurate knowledge of how many such events occurred at each redshift. Existing CSNR estimates are indirect, relying on star‑formation rate measurements, an assumed initial‑mass function, and a conversion factor from massive stars to supernovae. This indirect approach introduces a dominant systematic error that propagates directly into DSNB predictions, especially in the 10–26 MeV energy window where upcoming detectors (Super‑Kamiokande with Gd loading, Hyper‑Kamiokande, JUNO, DUNE) are most sensitive.

The authors propose that the next generation of wide‑field, time‑domain optical surveys—commonly referred to as “synoptic” surveys—will dramatically reduce this astrophysical uncertainty. Facilities such as the Large Synoptic Survey Telescope (LSST), Pan‑STARRS, and the Zwicky Transient Facility (ZTF) will repeatedly scan thousands of square degrees to depths of r ≈ 24.5 mag, providing near‑complete detection of supernovae out to redshift z ≈ 1. By directly counting supernovae in well‑characterized survey volumes, the CSNR can be measured with a statistical precision better than 5 % and with systematic errors that are largely controllable (e.g., through dust extinction corrections, host‑galaxy completeness studies, and spectroscopic typing). The paper’s Monte‑Carlo simulations show that, because the z < 1 universe contributes roughly 87 % of the DSNB event rate in the 10–26 MeV band, an accurate CSNR in this redshift range essentially fixes the astrophysical component of the DSNB flux. Consequently, the remaining uncertainty in the DSNB prediction will be dominated by neutrino‑physics inputs (average neutrino energy, spectral shape, flavor transformation), opening a direct window onto supernova core physics.

A second, equally compelling implication concerns “invisible” supernovae—core‑collapse events that either suffer extreme dust obscuration in their host galaxies or collapse directly to black holes without a luminous optical display. Such events would still emit the bulk of their binding‑energy in neutrinos, thereby augmenting the DSNB flux beyond what is expected from the optically‑measured CSNR. By comparing the precisely predicted DSNB (based on the synoptic‑survey CSNR) with the actual measured DSNB spectrum, one can infer the fraction of invisible supernovae. The authors illustrate that a 10 % contribution from direct‑collapse black‑hole forming events would raise the DSNB flux by a comparable amount, a shift that is detectable with a decade‑long exposure of a Gd‑enhanced Super‑Kamiokande detector.

The paper also discusses the practical challenges and systematic uncertainties that remain. Optical surveys must correct for host‑galaxy extinction, selection biases, and incomplete spectroscopic classification; these can be mitigated by multi‑wavelength follow‑up (infrared, radio, X‑ray) and by employing well‑tested light‑curve models. On the neutrino side, uncertainties in the emitted spectra (e.g., differences between electron‑type and heavy‑flavor neutrinos, collective oscillation effects) still affect the translation from a measured DSNB flux to core‑collapse physics. Nonetheless, the authors argue that the synergy between high‑precision CSNR measurements and next‑generation neutrino detectors will reduce the total error budget on the DSNB to the few‑percent level, a regime where meaningful constraints on supernova neutrino physics and on the population of invisible collapses become possible.

In summary, the paper demonstrates that forthcoming synoptic sky surveys will transform the DSNB from a qualitatively interesting but quantitatively uncertain signal into a precision probe of both stellar death and neutrino physics. By delivering a direct, high‑statistics measurement of the cosmic supernova rate out to z ≈ 1, these surveys will shrink the astrophysical uncertainty to ±5 %, allowing the DSNB to test models of neutrino emission, flavor conversion, and the prevalence of dust‑obscured or direct‑collapse supernovae. This interdisciplinary advance promises to link the emerging field of time‑domain astronomy with low‑energy neutrino astrophysics, paving the way for new discoveries about the life cycles of massive stars and the fundamental properties of neutrinos.