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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 in 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.

    

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2. Observing Intermediate-mass Black Holes and the Upper Stellar-mass gap with LIGO and Virgo

   https://doi.org/10.3847/1538-4357/ac3130  

   Mehta, Ajit Kumar ; Buonanno, Alessandra ; Gair, Jonathan ; Miller, M. Coleman ; Farag, Ebraheem ; deBoer, R. J. ; Wiescher, M. ; Timmes, F. X. ( January 2022 , The Astrophysical Journal)

   Abstract Using ground-based gravitational-wave detectors, we probe the mass function of intermediate-mass black holes (IMBHs) wherein we also include BHs in the upper mass gap at ∼60–130 M ⊙ . Employing the projected sensitivity of the upcoming LIGO and Virgo fourth observing run (O4), we perform Bayesian analysis on quasi-circular nonprecessing, spinning IMBH binaries (IMBHBs) with total masses 50–500 M ⊙ , mass ratios 1.25, 4, and 10, and dimensionless spins up to 0.95, and estimate the precision with which the source-frame parameters can be measured. We find that, at 2 σ , the mass of the heavier component of IMBHBs can be constrained with an uncertainty of ∼10%–40% at a signal-to-noise ratio of 20. Focusing on the stellar-mass gap with new tabulations of the 12 C( α , γ ) 16 O reaction rate and its uncertainties, we evolve massive helium core stars using MESA to establish the lower and upper edges of the mass gap as ≃ 59 − 13 + 34 M ⊙ and ≃ 139 − 14 + 30 M ⊙ respectively, where the error bars give the mass range that follows from the ±3 σ uncertainty in the 12 C( α , γ ) 16 O nuclear reaction rate. We find that high resolution of the tabulated reaction rate and fine temporal resolution are necessary to resolve the peak of the BH mass spectrum. We then study IMBHBs with components lying in the mass gap and show that the O4 run will be able to robustly identify most such systems. Finally, we reanalyze GW190521 with a state-of-the-art aligned-spin waveform model, finding that the primary mass lies in the mass gap with 90% credibility. 

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3. New Determination of the 12 C(α, γ) 16 O Reaction Rate and Its Impact on the Black-hole Mass Gap

   https://doi.org/10.3847/1538-4357/acb7de  

   Shen, Yangping ; Guo, Bing ; deBoer, Richard J. ; Li, Ertao ; Li, Zhihong ; Li, Yunju ; Tang, Xiaodong ; Pang, Danyang ; Adhikari, Sucheta ; Basu, Chinmay ; et al ( March 2023 , The Astrophysical Journal)

   We present a precise measurement of the asymptotic normalization coefficient (ANC) for the¹⁶O ground state (GS) through the¹²C(¹¹B,⁷Li)¹⁶O transfer reaction using the Quadrupole‐3‐Dipole (Q3D) magnetic spectrograph. The present work sheds light on the existing discrepancy of more than 2 orders of magnitude between the previously reported GS ANC values. This ANC is believed to have a strong effect on the¹²C(α,γ)¹⁶O reaction rate by constraining the external capture to the¹⁶O ground state, which can interfere with the high-energy tail of the 2⁺subthreshold state. Based on the new ANC, we determine the astrophysicalS-factor and the stellar rate of the¹²C(α,γ)¹⁶O reaction. An increase of up to 21% in the total reaction rate is found within the temperature range of astrophysical relevance compared with the previous recommendation of a recent review. Finally, we evaluate the impact of our new rate on the pair-instability mass gap for black holes (BH) by evolving massive helium core stars using the MESA stellar evolution code. The updated¹²C(α,γ)¹⁶O reaction rate decreases the lower and upper edges of the BH gap about 12% and 5%, respectively.

    

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4. Direct measurement of the 19 F( p , αγ ) 16 O reaction in JUNA

   https://doi.org/10.1051/epjconf/202226008004  

   Zhang, L.Y. ; Su, J. ; He, J.J. ; Wiescher, M. ; deBoer, R.J. ; Kahl, D. ; Chen, Y.J. ; Li, X.Y. ; Wang, J.G. ; Zhang, L. ; et al ( January 2022 , EPJ Web of Conferences)

   Liu, W. ; Wang, Y. ; Guo, B. ; Tang, X. ; Zeng, S. (Ed.)

   The 19 F( p , αγ ) 16 O reaction is of crucial importance for Galactic 19 F abundances and CNO cycle loss in first generation Population III stars. Due to its extremely small cross sections, the 19 F( p , αγ ) 16 O reaction has not been measured in the low energy part of the Gamow window(70-200 keV). As a day-one campaign, the experiment was performed under the extremely low cosmicray-induced background environment of the China JinPing Underground Laboratory(CJPL), one of the deepest underground laboratories in the world. The γ -ray yields were measured over E c . m . =72.4–344 keV, covering the full Gamow window for the first time. The direct experimental data will help people to expound the fluorine over-abundances, energy generation, as well as heavy-element nuclosynthesis scenario in asymptotic giant branch (AGB) stars, with the astrophysical model on the firm ground. 

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5. Threshold effects in the 10B(p,α)7Be, 12C(p,γ)13N and 14N(p,γ)15O reactions

   https://doi.org/10.3389/fphy.2022.1009489  

   Wiescher, M. ; deBoer, R.J. ; Görres, J. ( October 2022 , Frontiers in Physics)

   The typical energy range for charge particle interactions in stellar plasmas corresponds to a few 10s or 100s of keV. At these low energies, the cross sections are so vanishingly small that they cannot be measured directly with accelerator based experimental techniques. Thus, indirect studies of the compound structure near the threshold are used in the framework of reaction models to complement the direct data in order to extrapolate the cross section into the low energy regime. However, at the extremely small cross sections of interest, there maybe other quantum effects that modify the such extracted cross section. These may result from additional nuclear interactions associated with the threshold itself or could be due to other processes, such as electron screening. Measurements in plasma environments like at the OMEGA or National Ignition Facility facilities offer an entirely new set of experimental conditions for studying these types of reactions, often directly at the energies of interest. In this paper, we examine three reaction, 10 B( p , α ) 7 Be, 12 C( p , γ ) 13 N and 14 N( p , γ ) 15 O, which have all been measured at very low energies using accelerator based methods. All three reactions produce relatively long-lived radioactive nuclei, which can be collected and analyzed at plasma facilities using a variety of collection and identification techniques. 

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