More Like this

1. Resolving the Peak of the Black Hole Mass Spectrum

   https://doi.org/10.3847/1538-4357/ac8b83  

   Farag, Ebraheem ; Renzo, Mathieu ; Farmer, Robert ; Chidester, Morgan T. ; Timmes, F. X. ( October 2022 , The Astrophysical Journal)

   Gravitational-wave (GW) detections of binary black hole (BH) mergers have begun to sample the cosmic BH mass distribution. The evolution of single stellar cores predicts a gap in the BH mass distribution due to pair-instability supernovae (PISNe). Determining the upper and lower edges of the BH mass gap can be useful for interpreting GW detections of merging BHs. We useMESAto evolve single, nonrotating, massive helium cores with a metallicity ofZ= 10⁻⁵, until they either collapse to form a BH or explode as a PISN, without leaving a compact remnant. We calculate the boundaries of the lower BH mass gap for S-factors in the range S(300 keV) = (77,203) keV b, corresponding to the ±3σuncertainty in our high-resolution tabulated¹²C(α,γ)¹⁶O reaction rate probability distribution function. We extensively test temporal and spatial resolutions for resolving the theoretical peak of the BH mass spectrum across the BH mass gap. We explore the convergence with respect to convective mixing and nuclear burning, finding that significant time resolution is needed to achieve convergence. We also test adopting a minimum diffusion coefficient to help lower-resolution models reach convergence. We establish a new lower edge of the upper mass gap asM_lower≃${60}_{-14}^{+32}$M_⊙from the ±3σuncertainty inmore »the¹²C(α,γ)¹⁶O rate. We explore the effect of a larger 3αrate on the lower edge of the upper mass gap, findingM_lower≃${69}_{-18}^{+34}$M_⊙. We compare our results with BHs reported in the Gravitational-Wave Transient Catalog.

   « less
2. Radio Analysis of SN2004C Reveals an Unusual CSM Density Profile as a Harbinger of Core Collapse

   https://doi.org/10.3847/1538-4357/ac8c26  

   DeMarchi, Lindsay ; Margutti, R. ; Dittman, J. ; Brunthaler, A. ; Milisavljevic, D. ; Bietenholz, Michael F. ; Stauffer, C. ; Brethauer, D. ; Coppejans, D. ; Auchettl, K. ; et al ( October 2022 , The Astrophysical Journal)

   We present extensive multifrequency Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) observations of the radio-bright supernova (SN) IIb SN 2004C that span ∼40–2793 days post-explosion. We interpret the temporal evolution of the radio spectral energy distribution in the context of synchrotron self-absorbed emission from the explosion’s forward shock as it expands in the circumstellar medium (CSM) previously sculpted by the mass-loss history of the stellar progenitor. VLBA observations and modeling of the VLA data point to a blastwave with average velocity ∼0.06cthat carries an energy of ≈10⁴⁹erg. Our modeling further reveals a flat CSM density profileρ_CSM∝R^{−0.03±0.22}up to a break radiusR_br≈ (1.96 ± 0.10) × 10¹⁶cm, with a steep density gradient followingρ_CSM∝R^−2.3±0.5at larger radii. We infer that the flat part of the density profile corresponds to a CSM shell with mass ∼0.021M_☉, and that the progenitor’s effective mass-loss rate varied with time over the range (50–500) × 10⁻⁵M_☉yr⁻¹for an adopted wind velocityv_w= 1000 km s⁻¹and shock microphysical parametersϵ_e= 0.1,ϵ_B= 0.01. These results add to the mounting observational evidence for departures from the traditional single-wind mass-loss scenarios in evolved, massive stars in the centuries leading up to core collapse. Potentially viable scenarios include mass lossmore »powered by gravity waves and/or interaction with a binary companion.

   « less
3. Comparison of the Core-collapse Evolution of Two Nearly Equal-mass Progenitors

   https://doi.org/10.3847/1538-4357/acbb65  

   Bruenn, Stephen W. ; Sieverding, Andre ; Lentz, Eric J. ; Sukhbold, Tuguldur ; Hix, W. Raphael ; Huk, Leah N. ; Harris, J. Austin ; Messer, O. E. Bronson ; Mezzacappa, Anthony ( April 2023 , The Astrophysical Journal)

   We compare the core-collapse evolution of a pair of 15.8M_☉stars with significantly different internal structures, a consequence of the bimodal variability exhibited by massive stars during their late evolutionary stages. The 15.78 and 15.79M_☉progenitors have core masses (masses interior to an entropy of 4k_Bbaryon⁻¹) of 1.47 and 1.78M_☉and compactness parametersξ_1.75of 0.302 and 0.604, respectively. The core-collapse simulations are carried out in 2D to nearly 3 s postbounce and show substantial differences in the times of shock revival and explosion energies. The 15.78M_☉model begins exploding promptly at 120 ms postbounce when a strong density decrement at the Si–Si/O shell interface, not present in the 15.79M_☉progenitor, encounters the stalled shock. The 15.79M_☉model takes 100 ms longer to explode but ultimately produces a more powerful explosion. Both the larger mass accretion rate and the more massive core of the 15.79M_☉model during the first 0.8 s postbounce time result in largerν_e/${\overline{\nu }}_e$luminosities and RMS energies along with a flatter and higher-density heating region. The more-energetic explosion of the 15.79M_☉model resulted in the ejection of twice as much⁵⁶Ni. Most of the ejecta in both models are moderately proton rich, though counterintuitively the highest electron fraction (Y_e= 0.61) ejecta in either modelmore »are in the less-energetic 15.78M_☉model, while the lowest electron fraction (Y_e= 0.45) ejecta in either model are in the 15.79M_☉model.

   « less
4. Early-forming Massive Stars Suppress Star Formation and Hierarchical Cluster Assembly

   https://doi.org/10.3847/1538-4357/acb0c5  

   Lewis, Sean C. ; McMillan, Stephen L. W. ; Low, Mordecai-Mark Mac ; Cournoyer-Cloutier, Claude ; Polak, Brooke ; Wilhelm, Martijn J. C. ; Tran, Aaron ; Sills, Alison ; Zwart, Simon Portegies ; Klessen, Ralf S. ; et al ( February 2023 , The Astrophysical Journal)

   Feedback from massive stars plays an important role in the formation of star clusters. Whether a very massive star is born early or late in the cluster formation timeline has profound implications for the star cluster formation and assembly processes. We carry out a controlled experiment to characterize the effects of early-forming massive stars on star cluster formation. We use the star formation software suiteTorch, combining self-gravitating magnetohydrodynamics, ray-tracing radiative transfer,N-body dynamics, and stellar feedback, to model four initially identical 10⁴M_⊙giant molecular clouds with a Gaussian density profile peaking at 521.5 cm⁻³. Using theTorchsoftware suite through theAMUSEframework, we modify three of the models, to ensure that the first star that forms is very massive (50, 70, and 100M_⊙). Early-forming massive stars disrupt the natal gas structure, resulting in fast evacuation of the gas from the star-forming region. The star formation rate is suppressed, reducing the total mass of the stars formed. Our fiducial control model, without an early massive star, has a larger star formation rate and total efficiency by up to a factor of 3, and a higher average star formation efficiency per freefall time by up to a factor of 7. Early-forming massive stars promote the buildupmore »of spatially separate and gravitationally unbound subclusters, while the control model forms a single massive cluster.

   « less
5. Volumetric Rates of Luminous Red Novae and Intermediate-luminosity Red Transients with the Zwicky Transient Facility

   https://doi.org/10.3847/1538-4357/acc2b9  

   Karambelkar, Viraj R. ; Kasliwal, Mansi M. ; Blagorodnova, Nadejda ; Sollerman, Jesper ; Aloisi, Robert ; Anand, Shreya G. ; Andreoni, Igor ; Brink, Thomas G. ; Bruch, Rachel ; Cook, David ; et al ( May 2023 , The Astrophysical Journal)

   Luminous red novae (LRNe) are transients characterized by low luminosities and expansion velocities, and they are associated with mergers or common-envelope ejections in stellar binaries. Intermediate-luminosity red transients (ILRTs) are an observationally similar class with unknown origins, but they are generally believed to be either electron-capture supernovae in super-asymptotic giant branch stars or outbursts in dusty luminous blue variables (LBVs). In this paper, we present a systematic sample of eight LRNe and eight ILRTs detected as part of the Census of the Local Universe (CLU) experiment on the Zwicky Transient Facility (ZTF). The CLU experiment spectroscopically classifies ZTF transients associated with nearby (<150 Mpc) galaxies, achieving 80% completeness form_r< 20 mag. Using the ZTF-CLU sample, we derive the first systematic LRNe volumetric rate of${7.8}_{-3.7}^{+6.5}\times {10}^{-5}$Mpc⁻³yr⁻¹in the luminosity range −16 ≤M_r≤ −11 mag. We find that, in this luminosity range, the LRN rate scales as$\mathit{dN}/\mathit{dL}\propto L^{-2.5\pm 0.3}$—significantly steeper than the previously derived scaling ofL^−1.4±0.3for lower-luminosity LRNe (M_V≥ −10 mag). The steeper power law for LRNe at high luminosities is consistent with the massive merger rates predicted by binary population synthesis models. We find that the rates of the brightest LRNe (M_r≤ −13 mag) aremore »consistent with a significant fraction of them being progenitors of double compact objects that merge within a Hubble time. For ILRTs, we derive a volumetric rate of${2.6}_{-1.4}^{+1.8}\times {10}^{-6}$Mpc⁻³yr⁻¹forM_r≤ −13.5 mag, which scales as$\mathit{dN}/\mathit{dL}\propto L^{-2.5\pm 0.5}$. This rate is ∼1%–5% of the local core-collapse supernova rate and is consistent with theoretical ECSN rate estimates.

   « less