Core-collapse Supernovae Research Articles

Shock cooling emission from explosions of massive stars – III. Blue supergiants

ABSTRACT Light emission in the first hours and days following core-collapse supernovae is dominated by the escape of photons from the expanding shock-heated envelope. In preceding papers, we provided a simple analytic description of the time-dependent luminosity, L, and colour temperature, $T_{\rm col}$, as well as of the small (${\simeq} 10 {{\, \rm per\, cent}}$) deviations of the spectrum from a blackbody at low frequencies, $h\nu \lt 3T_{\rm col}$, and of ‘line dampening’ at $h\nu \gt 3T_{\rm col}$, for explosions of red supergiants (RSGs) with convective polytropic envelopes (without significant circumstellar medium). Here, we extend our work to provide similar analytic formulae for explosions of blue supergiants with radiative polytropic envelopes. The analytic formulae are calibrated against a large set of spherically symmetric multigroup (frequency-dependent) calculations for a wide range of progenitor parameters (mass, radius, and core/envelope mass ratios) and explosion energies. In these calculations, we use the opacity tables we constructed (and made publicly available), which include the contributions of bound–bound and bound–free transitions. The analytic formulae reproduce the numeric L and $T_{\rm col}$ to within 10 and 5 per cent accuracy, and the spectral energy distribution to within ${\sim} 20\!-\!40 {{\, \rm per\, cent}}$. The accuracy is similar to that achieved for RSG explosions.

Strong Chemical Tagging in FIRE: Intra- and Intercluster Chemical Homogeneity in Open Clusters in Milky Way–like Galaxy Simulations

Open-star clusters are the essential building blocks of the Galactic disk; “strong chemical tagging”—the premise that all star clusters can be reconstructed given chemistry information alone—is a driving force behind many current and upcoming large Galactic spectroscopic surveys. In this work, we characterize the abundance patterns for nine elements (C, N, O, Ne, Mg, Si, S, Ca, and Fe) in open clusters (OCs) in three galaxies (m12i, m12f, and m12m) from the Latte suite of FIRE-2 simulations, to investigate the feasibility of strong chemical tagging in these simulations. We select young massive (≥104.6 M ⊙) OCs formed in the last ∼100 Myr and calculate the intra- and intercluster abundance scatter for these clusters. We compare these results with analogous calculations drawn from observations of OCs in the Milky Way. We find the intracluster scatter of the observations and simulations to be comparable. While the abundance scatter within each cluster is minimal (≲0.020 dex), the mean abundance patterns of different clusters are not unique. We also calculate the chemical difference in intra- and intercluster star pairs and find it, in general, to be so small that it is difficult to distinguish between stars drawn from the same OC or from different OCs. Despite tracing three distinct nucleosynthetic families (core-collapse supernovae, white dwarf supernovae, and stellar winds), we conclude that these elemental abundances do not provide enough discriminating information to use strong chemical tagging for reliable OC membership.

A Systematic Search for Rapid Transients in the Subaru HSC-SSP Transient Survey

Recent high-cadence transient surveys have discovered rapid transients whose light-curve timescales are shorter than those of typical supernovae (SNe). In this paper, we present a systematic search for rapid transients at medium-high redshifts among 3381 SNe candidates obtained from the Hyper Suprime-Cam Subaru Strategic Program transient survey. We developed a machine learning classifier to classify the SN candidates into four types (Type Ia, Ibc, II SNe and rapid transients) based on the features derived from the light curves. By applying this classifier to the 3381 SN candidates and by further applying the quality cut, we selected 14 rapid transient samples. They are located at a wide range of redshifts (0.34 ≤ z ≤ 1.85) and show a wide range of the peak absolute magnitude (−17 ≥ M ≥ −22). The event rate of the rapid transients is estimated to be ∼6 × 103 events yr−1 Gpc−3 at z ∼ 0.74, which corresponds to about 2% of the event rate of normal core-collapse SNe at a similar redshift. Based on the luminosity and color evolution, we selected two candidates of Type Ibn SNe at z ∼ 0.75. The event rate of Type Ibn SN candidates is more than 1% of Type Ib SN rate at the same redshift, suggesting that this fraction of massive stars at this redshift range eruptively ejects their He-rich envelope just before the explosions. Also, two objects at z = 1.37 and 1.85 show high luminosities comparable to superluminous SNe. Their event rate is about 10%–25% of superluminous SNe at z ∼ 2.

Study of late-time ultraviolet emission in core collapse supernovae and its implications for the peculiar transient AT2018cow

Over time, core-collapse supernova (CCSN) spectra become redder due to dust formation and cooling of the SN ejecta. An ultraviolet (UV) detection of a CCSN at late times will thus indicate an additional physical process, such as an interaction between the SN ejecta and the circumstellar material, or viewing down to the central engine of the explosion. Both of these models have been proposed to explain the peculiar transient AT2018cow, a luminous fast blue optical transient detected in the UV two to four years after the event, with only marginal fading over this time period. To identify whether the late-time UV detection of AT2018cow could indicate that it is a CCSN, we investigate whether CCSNe are detectable in the UV between two and five years after the explosion. We determine how common late-time UV emission in CCSNe is and compare those CCSNe detected in the UV to the peculiar transient AT2018cow. We used a sample of 51 nearby (z<0.065) CCSNe observed with the Hubble Space Telescope within two to five years of discovery. We measured their brightness or determined an upper limit on the emission through an artificial star experiment in cases of no detection. For two CCSNe, we detected a point source within the uncertainty region of the SN position. Both have a low chance alignment probability with bright objects within their host galaxies. Therefore, they are likely to be related to their SNe, which are both known to be interacting SNe. Comparing the absolute UV magnitude of AT2018cow at late times to the absolute UV magnitudes of the two potential SN detections, there is no evidence that a late-time UV detection of AT2018cow is atypical for interacting SNe. However, when limiting the sample to CCSNe closer than AT2018cow, we see that it is brighter than the upper limits on most CCSN non-detections. Combined with a very small late time photospheric radius of this leads us to conclude that the late-time UV detection of AT2018cow was not driven by interaction. Instead, it suggests that we are possibly viewing the inner region of the explosion that is perhaps due to the long-lived presence of an accretion disc. Such properties are naturally expected in tidal disruption models and are less straightforward (though not impossible) in SN scenarios.

WTP 19aalnxx: Discovery of a Bright Mid-infrared Transient in the Emerging Class of Low-luminosity Supernovae Revealed by Delayed Circumstellar Interaction

While core-collapse supernovae (SNe) often show early and consistent signs of circumstellar medium (CSM) interaction, some exhibit delayed signatures due to interaction with distant material around the progenitor star. Here we present the discovery in NEOWISE data of WTP 19aalnxx, a luminous mid-infrared (MIR) transient in the outskirts of the galaxy KUG 0022-007 at ≈190 Mpc. First detected in 2018, WTP 19aalnxx reaches a peak absolute (Vega) magnitude of ≈−22 at 4.6 μm in ≈3 yr, comparable to the most luminous interacting SNe. Archival data reveal a ≳5× fainter optical counterpart detected since 2015, while follow-up near-infrared observations in 2022 reveal an extremely red (Ks − W2 ≈ 3.7 mag) active transient. Deep optical spectroscopy confirm strong CSM interaction signatures via intermediate-width Balmer emission lines and coronal metal lines. Modeling the broadband spectral energy distribution, we estimate the presence of ≳10−2 M ⊙ of warm dust, likely formed in the cold dense shell. Together with the lack of nebular Fe emission, we suggest that WTP 19aalnxx is a missed, low (optical) luminosity SN in an emerging family of core-collapse SNe distinguished by their CSM-interaction-powered MIR emission that outshines the optical bands. Investigating the Zwicky Transient Facility sample of SNe with NEOWISE data, we find 16 core-collapse SNe (≳3% in a volume-limited sample) without early signs of CSM interaction that exhibit delayed IR brightening, suggestive of dense CSM shells at ≲1017 cm. We suggest that synoptic IR surveys offer a new route to revealing late-time CSM interaction and the prevalence of intense terminal mass loss in massive stars.

A Promising Approach for Determining Neutrino Mass Hierarchy by Using Supernova Neutrino Detections

The determination of neutrino mass hierarchy is crucial for particle physics, astrophysics, and cosmology. In this work, we propose an easy-to-use method to determine the neutrino hierarchy based on core-collapse supernova (CCSN) neutrino detections. By analyzing the expected event rates of the neutrino burst at a terrestrial water Cherenkov detector, we found that the event rates predicted by the normal and inverted hierarchy models have marked differences in the neutrino energy range 10 ∼ 20 MeV and the postbounce time <0.5 s. Within this specific energy and time range, the analytical relationship between the cumulative event number and proto–neutron star (PNS) baryon mass is extracted. Based on the normal and inverted hierarchy models, two different PNS masses can be inferred from this relationship by using the time profile of neutrino events. Then, the neutrino hierarchy can be determined by comparing the PNS mass inferred from the neutrino detections and the electromagnetic or gravitational-wave channels. Furthermore, the nonadiabatic part of the Mikheyev–Smirnov–Wolfenstein flavor conversions may also be quantified with this method, which would be very helpful for the studies of the explosion mechanism and nucleosynthesis of CCSNe.

A Young Super Star Cluster Powering a Nebula of Retained Massive Star Ejecta

We suggest that “Godzilla” of the lensed Sunburst galaxy (z = 2.37) is a young super star cluster powering a nebula of gravitationally trapped stellar ejecta. Employing Hubble Space Telescope photometry and spectroscopy from the Very Large Telescope (VLT) MUSE and VLT/X-Shooter, we infer the physical and chemical properties of the cluster and nebula, finding that Godzilla is young, 4–6 Myr; massive, 2 × 106 M ⊙ (1000/μ); of stellar metallicity, Z ≃ 0.25 Z ⊙; and has a compact far-UV component of ≲1 pc (1000/μ), where μ is the flux magnification factor. The gas is significantly enriched with N and He, indicating stellar wind material, and has highly elevated O relative to the stellar metallicity, indicating entrainment of core-collapse supernova (CCSN) ejecta. The high density, n e ≃ 107−8 cm−3, implies a highly pressurized intracluster environment. We propose that the pressure results from CCSN-driven supersonic turbulence in warm, self-shielding gas, which has accumulated in the cluster center after runaway radiative cooling and is dense enough to resist removal by CCSNe. The nebula gas shows subsolar C/O, Ne/O, and Si/O, which may reflect the CCSN element yields for initial stellar masses >40 M ⊙. A comparison to element yield synthesis models for young star clusters shows that the gas abundances are consistent with complete retention and mixture of stellar winds and CCSN ejecta until the inferred cluster age. The inferred O and He enhancement may have implications for the formation of multiple stellar populations in globular clusters, as stars formed from this gas would contradict the observed abundances of second-population stars.

The long-term influence of a magnetar power in stripped-envelope supernovae. Radiative-transfer modeling of He-star explosions from 1 to 10 years

Much interest surrounds the nature of the compact remnant that formed in core collapse supernovae (SNe). One means to constrain its nature is to search for signatures of power injection from the remnant in the SN observables years after explosion. In this work, we conduct a large grid of 1D nonlocal thermodynamic equilibrium radiative transfer calculations of He-star explosions under the influence of magnetar-power injection from post-explosion age of about one to ten years. Our results for SN observables vary with He-star mass, SN age, injected power, or ejecta clumping. At high mass (model he12p00), the ejecta coolants are primarily O and Ne, with and dominating in the optical, and with strong in the infrared -- this line may carry more than half the total SN luminosity. For lower He-star masses (models he6p00 and he3p30), a greater diversity of coolants appear, in particular Fe, S, Ar, or Ni from the Si- and Fe-rich regions. All models tend to rise in ionization in time, with twice-ionized species (i.e., O Ne S or Fe dominating at sim \,10\,yr, although this ionization is significantly reduced if clumping is introduced. Our treatment of magnetar power in the form of high-energy electrons or X-ray irradiation yields similar results -- no X-rays emerge from our ejecta even at ten years because of high-optical depth in the kilo-electronvolt range. An uncertainty of our work concerns the power deposition profile, which is not known from first principles, although this profile could be constrained from observations. Our magnetar-powered model he8p00 with moderate clumping yields a good match to the optical and near-infrared observations of Type Ib SN\,2012au at both 289--335\,d (power of $1-2 and 2269\,d (power of 1040\ Unless overly ionized (i.e., if the optical spectrum shows only strong we find that all massive magnetar-powered ejecta should be infrared luminous at 5--10\,yr through strong line emission.

Enhanced production of 60Fe in massive stars.

Massive stars are a major source of chemical elements in the cosmos, ejecting freshly produced nuclei through winds and core-collapse supernova explosions into the interstellar medium. Among the material ejected, long-lived radioisotopes, such as 60Fe (iron) and 26Al (aluminum), offer unique signs of active nucleosynthesis in our galaxy. There is a long-standing discrepancy between the observed 60Fe/26Al ratio by γ-ray telescopes and predictions from supernova models. This discrepancy has been attributed to uncertainties in the nuclear reaction networks producing 60Fe, and one reaction in particular, the neutron-capture on 59Fe. Here we present experimental results that provide a strong constraint on this reaction. We use these results to show that the production of 60Fe in massive stars is higher than previously thought, further increasing the discrepancy between observed and predicted 60Fe/26Al ratios. The persisting discrepancy can therefore not be attributed to nuclear uncertainties, and points to issues in massive-star models.

Preferential occurrence of fast radio bursts in massive star-forming galaxies.

Fast radio bursts (FRBs) are millisecond-duration events detected from beyond the Milky Way. FRB emission characteristics favour highly magnetized neutron stars, or magnetars, as the sources1, as evidenced by FRB-like bursts from a galactic magnetar2,3, and the star-forming nature of FRB host galaxies4,5. However, the processes that produce FRB sources remain unknown6. Although galactic magnetars are often linked to core-collapse supernovae (CCSNe)7, it is uncertain what determines which supernovae result in magnetars. The galactic environments of FRB sources can be used to investigate their progenitors. Here, we present the stellar population properties of 30 FRB host galaxies discovered by the Deep Synoptic Array (DSA-110). Our analysis shows a marked deficit of low-mass FRB hosts compared with the occurrence of star formation in the Universe, implying that FRBs are a biased tracer of star formation, preferentially selecting massive star-forming galaxies. This bias may be driven by galaxy metallicity, which is positively correlated with stellar mass8. Metal-rich environments may favour the formation of magnetar progenitors through stellar mergers9,10, as higher-metallicity stars are less compact and more likely to fill their Roche lobes, leading to unstable mass transfer. Although massive stars do not have convective interiors to generate strong magnetic fields by dynamo11, merger remnants are thought to have the requisite internal magnetic-field strengths to result in magnetars11,12. The preferential occurrence of FRBs in massive star-forming galaxies suggests that a core-collapse supernova of merger remnants preferentially forms magnetars.

A survey of extremely metal-poor gas at cosmic noon

Aims. We aim to study the high-precision chemical abundances of metal-poor gas clouds at cosmic noon (2 &lt; z &lt; 4) and investigate the associated enrichment histories. Methods. We analyze the abundances of four newly discovered metal-poor gas clouds utilizing observations conducted with Keck/HIRES and VLT/UVES. These systems are classified as very metal-poor (VMP), with [Fe/H] &lt; −2.57, and one system qualifies as an extremely metal-poor (EMP) Damped Lyman-α (DLA) system with [Fe/H] = −3.13 ± 0.06. In combination with new high-resolution data of two previously known EMP DLAs and 2 systems reported in the literature, we conduct a comprehensive analysis of eight of the most metal-poor gas clouds currently known. We focus on high-precision abundance measurements using the elements: C, N, O, Al, Si, and Fe. Results. Our findings indicate increasing evidence of elevated [O/Fe] abundances when [Fe/H] &lt; −3. EMP DLAs are well-modeled with a mean value of [O/Fe]cen = +0.50 ± 0.04 and an intrinsic scatter of σint[O/Fe] = 0.13-0.04+0.06. While VMP DLAs are well-modeled with [O/Fe]cen = +0.40 ± 0.02 and σint, [O/Fe] = 0.06 ± 0.02. We further find tentative evidence of a redshift evolution of [C/O] across these most metal-poor DLAs with lower redshift systems showing elevated [C/O] ratios. Using the measured abundances, combined with a stochastic chemical enrichment model, we investigate the properties of the stellar population responsible for enriching EMP gas at cosmic noon. We find that the chemistry of these systems is best explained via the enrichment of just two massive progenitors, N⋆ = 2 ± 1, that ended their lives as core collapse SNe with a typical explosion energy Eexp = (1.6 ± 0.6)×1051 erg. These progenitors formed obeying a Salpeter-like power-law IMF, where all stars of mass greater than Mmax = 32-4+10M⊙ collapse directly to black holes and do not contribute to the metal enrichment.

Identifying Jittering Jet-shaped Ejecta in the Cygnus Loop Supernova Remnant

Analyzing images of the Cygnus Loop, a core-collapse supernova (CCSN) remnant, in different emission bands, we identify a point-symmetrical morphology composed of three symmetry axes that we attribute to shaping by three pairs of jets. The main jet axis has an elongated S shape, appearing as a faint narrow zone in visible and UV. We term it the S-shaped hose, and the structure of three symmetry lines the point-symmetric wind rose. The two other lines connect a protrusion (an ear or a bulge) with a hole on the opposite side of the center (a nozzle or a cavity), structures that we identify in the X-ray, UV, visible, IR, and/or radio images. There is a well-known blowout at the southern end of the S-shaped hose, and we identify a possible opposite blowout at the northern end of the S-shaped hose. The point-symmetrical morphology of the Cygnus Loop is according to the expectation of the jittering jets explosion mechanism (JJEM) of CCSNe, where several to few tens of pairs of jets with stochastically varying directions explode the star. The three pairs of jets that shaped the wind-rose structure of the Cygnus Loop are the last energetic pairs of this series of jets. Our study further supports the JJEM as the main explosion mechanism of CCSNe.

Generating tailored high frequency features in core collapse supernova gravitational wave signals applicable in LIGO interferometric studies

In this article, we introduce a methodology based on an analytical model of a damped harmonic oscillator subject to random forcing to generate transient gravitational wave signals. Such a model incorporates a simulated linear high-frequency component that mirrors the growing characteristic frequency over time observed in numerical simulations of core-collapse supernova gravitational wave signals. Unlike traditional numerical simulations, the method proposed in this study requires minimal computational resources, which makes it particularly advantageous for tasks such as data analysis, detection, and reconstruction of gravitational wave transients. To verify the physical accuracy of the generated signals, they are compared against the amplitude spectral of current LIGO interferometers and a 3D numerical simulation of a core-collapse supernova gravitational wave signal from the Andresen et al. 2017 model s15.nr. The results indicate that this approach is effective in generating scalable signals that align with LIGO interferometric data, offering potential utility in various gravitational wave transient investigations.

The next galactic supernova can uncover mass and couplings of particles decaying to neutrinos

Many particles predicted by extensions of the Standard Model feature interactions with neutrinos, e.g., Majoron-like bosons ϕ. If the mass of ϕ is larger than about 10 keV, they can be produced abundantly in the core of the next galactic core-collapse supernova through neutrino coalescence, and leave it with energies of around 100 MeV. Their subsequent decay to high-energy neutrinos and anti-neutrinos provides a distinctive signature at Earth. Ongoing and planned neutrino and dark matter experiments allow us to reconstruct the energy, flavor, and time of arrival of these high-energy neutrinos. For the first time, we show that these measurements can help pinpointing the mass of ϕ and its couplings to neutrinos of different flavor. Our results can be generalized in a straightforward manner to other hypothetical feebly interacting particles, like novel gauge bosons or heavy neutral leptons, that decay into neutrinos.

Neutrino quantum kinetics in two spatial dimensions

Our understanding of neutrino flavor conversion in the innermost regions of core-collapse supernovae and neutron star mergers is mostly limited to spherically symmetric configurations that facilitate the numerical solution of the quantum kinetic equations. In this paper, we simulate neutrino quantum kinetics within a (2+1+1) dimensional setup: we model the flavor evolution during neutrino decoupling from matter in two spatial dimensions, one neutrino momentum variable, and time; taking into account non-forward neutral current and charged current collisions of neutrinos with the matter background, as well as neutrino advection. In order to mimic fluctuations in the neutrino emission and matter background, and explore their effect on the flavor evolution, we introduce perturbations in the collision term as well as in the vacuum term of the Hamiltonian. Because of such perturbations, the initial symmetry of the neutrino field across the simulation annulus is broken and flavor conversion is qualitatively affected, with regions of larger flavor conversion alternating across the simulation annulus. In addition, neutrino advection is responsible for spreading flavor waves across neighboring spatial regions. Although based on a simplified setup, our findings highlight the importance of modeling neutrino quantum kinetics in multi-dimensions to assess the impact of neutrinos on the physics of compact astrophysical sources and nucleosynthesis.

Evidence for Type Ib/c Origin of the Supernova Remnant G292.0+1.8

Circumstellar material (CSM) produced by mass loss from massive stars (≳10 M ⊙) through strong stellar winds or binary stripping provides rich information for understanding progenitors of core-collapse supernova remnants. In this paper we present a grating spectroscopy of a Galactic SNR G292.0+1.8, which is claimed to be a Type Ib/c remnant in a binary system according to recent studies. If G292.0+1.8 had experienced a strong mass-loss via binary interactions before its explosion, an oxygen-rich material produced in the He-burning layer is expected to be observed in the central belt-like structure formed by shock-heated CSM. Using the Reflection Grating Spectrometer onboard XMM-Newton, we detect N vii Lyα line (0.50 keV) for the first time in G292.0+1.8 and find that the abundance ratio of nitrogen to oxygen is significantly lower (N/O = 0.5 ± 0.1) than the solar value. This low N/O suggests that the progenitor of G292.0+1.8 experienced strong mass-loss and ended up as a Wolf–Rayet star exposing the He-burning layer at the presupernova. Comparing our result and the evolution models of single stars and binaries, we conclude that the progenitor of G292.0+1.8 experienced strong enough mass-loss to occur a Type Ib/c supernova. Our finding is another crucial piece of evidence for a stripped-envelope supernova such as Type Ib/c as the origin of G292.0+1.8.

A census of the Sun’s ancestors and their contributions to the Solar System chemical composition

In this work, we compute the rates and numbers of different types of stars and phenomena (supernovae, novae, white dwarfs, merging neutron stars, black holes) that contributed to the chemical composition of the Solar System. During the Big Bang, only light elements formed, while all the heavy ones, from carbon to uranium and beyond, have since been created inside stars. Stars die and release the newly formed elements into the interstellar gas. This process is called ‘chemical evolution’. In particular, we analyse the death rates of stars of all masses, whether they die quiescently or explosively. These rates and total star numbers are computed in the context of a revised version of the two-infall model for the chemical evolution of the Milky Way, which reproduces the observed abundance patterns of several chemical species, the global solar metallicity, and the current gas, stellar, and total surface mass densities relatively well. We also compute the total number of stars ever born and still alive as well as the number of stars born up to the formation of the Solar System with mass and metallicity like those of the Sun. This latter number accounts for all the possible existing Solar systems that can host life in the solar vicinity. We conclude that, among all the stars (from 0.8 to 100 M⊙) that were born and died from the Big Bang up until the Solar System formation epoch and that contributed to its chemical composition, 93.00% were stars that died as single white dwarfs (without interacting significantly with a companion star) and originated in the mass range of 0.8–8 M⊙, while 5.24% were neutron stars and 0.73% were black holes, both originating from core-collapse supernovae (M &gt; 8 M⊙); 0.64% were Type Ia supernovae and 0.40% were nova systems, both originating from the same mass range as the white dwarfs. The number of stars similar to the Sun born from the Big Bang up until the formation of the Solar System, with metallicity in the range 12+log(Fe/H)= 7.50 ± 0.04 dex, is ~31•107, and in particular our Sun is the ~2.61• 107-th star of this kind.

SDSS J0018-0939: A Clear Signature of Sub-Chandrasekhar Mass Type 1a Supernova

Very metal-poor (VMP) stars ([Fe/H] ≤ −2) that have subsolar values of [X/Fe] for α elements such as Mg, Si, and Ca, are referred to as α-poor VMP stars. They are quite rare among VMP stars and are thought to have formed from gas enriched predominantly by a single Type Ia supernova (SN 1a) in contrast to most VMP stars, which are α-enhanced and usually associated with core-collapse supernovae. The observed abundance pattern in such stars can provide a direct way to probe the nucleosynthesis in individual SN 1a. Although the abundance patterns in some α-poor VMP stars have been shown to be consistent with SN 1a ejecta, a clear nucleosynthetic signature for SN 1a resulting from the explosion of a near Chandrasekhar mass (near-M Ch) or a sub-Chandrasekhar mass (sub-M Ch) white dwarf, has not been unambiguously detected. We perform a detailed analysis of various formation channels of VMP stars and find that the α-poor VMP star SDSS J0018-0939, which was earlier reported as a star with potential pair-instability supernova origin, provides a near-smoking-gun signature of a sub-M Ch SN 1a resulting from He detonation. We find that compared to other α-poor VMP stars that were previously identified with SN 1a, SDSS J0018-0939 is the only star that has a clear and unambiguous signature of SN 1a. Interestingly, our results are consistent with constraints on SN1 a from recent galactic chemical evolution studies that indicate that sub-M Ch SN 1a accounts for ∼50%–75% of all SN 1a and is possibly the dominant channel in the early Galaxy.

Pulsar-wind nebulae meeting the circumstellar media of their progenitors

A significative fraction of high-mass stars sail away through the interstellar medium of the galaxies. Once they evolved and died via a core-collapse supernova, a magnetised, rotating neutron star (a pulsar) is usually left over. The immediate surroundings of the pulsar is the pulsar wind, which forms a nebula whose morphology is shaped by the supernova ejecta and channelled into the circumstellar medium of the progenitor star in the pre-supernova time. Irregular pulsar-wind nebulae display a large variety of radio appearances, screened by their interacting supernova blast wave, or harbour asymmetric up–down emission. Here, we present a series of 2.5-dimensional (2 dimensions for the scalar quantities plus a toroidal component for the vectors) black non-relativistic magneto-hydrodynamical simulations exploring the evolution of the pulsar-wind nebulae generated by a red supergiant and a Wolf-Rayet massive supernova progenitor, moving with Mach number $M=1$ and $M=2$ into the warm phase of the Galactic plane. black In such a simplified approach, the progenitor's direction of motion, the local ambient medium magnetic field, and the progenitor and pulsar axis of rotation, are all aligned; this restricted our study to peculiar pulsar-wind nebula of high-equatorial-energy flux. We find that the reverberation of the termination shock of the pulsar-wind nebulae, when sufficiently embedded into its dead stellar surroundings and interacting with the supernova ejecta, is asymmetric and differs greatly as a function of the past circumstellar evolution of its progenitor, which reflects into their projected radio synchrotron emission. This mechanism is particularly at work in the context of remnants involving slowly moving or very massive stars. We find that the mixing of material in plerionic core-collapse supernova remnants is strongly affected by the asymmetric reverberation in their pulsar-wind nebulae.

Lower-mass-gap Black Holes in Dense Star Clusters

The existence of compact stellar remnants in the mass range 2–5 M ⊙ has long been debated. This so-called lower-mass gap (LMG) was initially suggested by the lack of low-mass X-ray binary observations with accretors about 2–5 M ⊙, but it has recently been called into question following newer observations, including an LMG candidate with a millisecond pulsar (MSP) companion in the dense globular cluster NGC 1851. Here, we model NGC 1851 with a grid of similar dense star clusters utilizing the state-of-the-art Monte Carlo N-body code Cluster Monte Carlo, and we specifically study the formation of LMG black holes (BHs). We demonstrate that both massive star evolution and dynamical interactions can contribute to forming LMG BHs. In general, the collapse of massive remnants formed through mergers of neutron stars (NSs) or massive white dwarfs produces the largest number of LMG BHs among all formation channels. However, in more massive clusters, supernova core collapse can contribute comparable numbers. Our NGC 1851-like models can reproduce MSP—LMG BH binaries similar to the observed system. Additionally, the LMG BHs can also become components of dynamically assembled binaries, and some will be in merging BH–NS systems similar to the recently detected gravitational wave source GW230529. However, the corresponding merger rate is probably ≲1 Gpc−3 yr−1.