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1. GW231123: A Binary Black Hole Merger with Total Mass 190–265 M _⊙

   https://doi.org/10.3847/2041-8213/ae0c9c  

   Abac, A G; Abouelfettouh, I; Acernese, F; Ackley, K; Adamcewicz, C; Adhicary, S; Adhikari, D; Adhikari, N; Adhikari, R X; Adkins, V K; et al (October 2025, The Astrophysical Journal Letters)

   Abstract On 2023 November 23, the two LIGO observatories both detected GW231123, a gravitational-wave signal consistent with the merger of two black holes with masses $137_{-18}^{+23}{M}_{\odot }$and $101_{-50}^{+22}{M}_{\odot }$(90% credible intervals), at a luminosity distance of 0.7–4.1 Gpc, a redshift of $0.40_{-0.25}^{+0.27}$, and with a network signal-to-noise ratio of ∼20.7. Both black holes exhibit high spins— $0.90_{-0.19}^{+0.10}$and $0.80_{-0.52}^{+0.20}$, respectively. A massive black hole remnant is supported by an independent ringdown analysis. Some properties of GW231123 are subject to large systematic uncertainties, as indicated by differences in the inferred parameters between signal models. The primary black hole lies within or above the theorized mass gap where black holes between 60–130M_⊙should be rare, due to pair-instability mechanisms, while the secondary spans the gap. The observation of GW231123 therefore suggests the formation of black holes from channels beyond standard stellar collapse and that intermediate-mass black holes of mass ∼200M_⊙form through gravitational-wave-driven mergers. 

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2. Reconstructing the Genealogy of LIGO-Virgo Black Holes

   https://doi.org/10.3847/1538-4357/ad781b  

   Mahapatra, Parthapratim; Chattopadhyay, Debatri; Gupta, Anuradha; Antonini, Fabio; Favata, Marc; Sathyaprakash, B S; Arun, K G (October 2024, The Astrophysical Journal)

   Abstract We propose a Bayesian inference framework to predict the merger history of LIGO-Virgo binary black holes (BHs), whose binary components may have undergone hierarchical mergers in the past. The framework relies on numerical relativity predictions for the mass, spin, and kick velocity of the remnant BHs. This proposed framework computes the masses, spins, and kicks imparted to the remnant of the parent binaries, given the initial masses and spin magnitudes of the binary constituents. We validate our approach by performing an “injection study” based on a constructed sequence of hierarchically formed binaries. Noise is added to the final binary in the sequence, and the parameters of the “parent” and “grandparent” binaries in the merger chain are then reconstructed. This method is then applied to three GWTC-3 events: GW190521, GW200220_061928, and GW190426_190642. These events were selected because at least one of the binary companions lies in the putative pair-instability supernova mass gap, in which stellar processes alone cannot produce BHs. Hierarchical mergers offer a natural explanation for the formation of BHs in the pair-instability mass gap. We use the backward evolution framework to predict the parameters of the parents of the primary companion of these three binaries. For instance, the parent binary of GW190521 has masses ${72}_{-22}^{+32}{M}_{\odot }$and ${31}_{-23}^{+24}{M}_{\odot }$within the 90% credible interval. Astrophysical environments with escape speeds ≥100 km s⁻¹are preferred sites to host these events. Our approach can be readily applied to future high-mass gravitational wave events to predict their formation history under the hierarchical merger assumption. 

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3. KMT-2022-BLG-0086: Another Binary-lens Binary-source Microlensing Event

   https://doi.org/10.3847/1538-3881/ade2e7  

   Chung, Sun-Ju; Hwang, Kyu-Ha; Yee, Jennifer C; Gould, Andrew; Bond, Ian A; Yang, Hongjing; Albrow, Michael D; Jung, Youn Kil; Han, Cheongho; Ryu, Yoon-Hyun; et al (July 2025, The Astronomical Journal)

   Abstract We present the analysis of a microlensing event KMT-2022-BLG-0086 of which the overall light curve is not described by a binary-lens single-source (2L1S) model, which suggests the existence of an extra lens or an extra source. We found that the event is best explained by the binary-lens binary-source (2L2S) model, but the 2L2S model is only favored over the triple-lens single-source (3L1S) model by Δχ² ≃ 9. Although the event has noticeable anomalies around the peak of the light curve, they are not enough covered to constrain the angular Einstein radiusθ_E, thus we only measure the minimum angular Einstein radius ${\theta }_{\mathrm{E},\min }$. From the Bayesian analysis, it is found that that the binary lens system is a binary star with masses of $(m_1,m_2)=(0.46_{-0.25}^{+0.35}{M}_{\odot },0.75_{-0.55}^{+0.67}{M}_{\odot })$at a distance of $D_{\mathrm{L}}=5.87_{-1.79}^{+1.21}$kpc, while the triple lens system is a brown dwarf or a massive giant planet in a low-mass binary-star system with masses of $(m_1,m_2,m_3)=(0.43_{-0.35}^{+0.41}{M}_{\odot },0.056_{-0.047}^{+0.055}{M}_{\odot }$, $20.84_{-17.04}^{+20.20}{M}_{\mathrm{J}})$at a distance of $D_{\mathrm{L}}=4.06_{-3.28}^{+1.39}$kpc, indicating a disk lens system. The 2L2S model yields the relative lens-source proper motion ofμ_rel ≥ 4.6 mas yr⁻¹that is consistent with the Bayesian result, whereas the 3L1S model yieldsμ_rel ≥ 18.9 mas yr⁻¹, which is more than three times larger than that of a typical disk object of ∼6 mas yr⁻¹and thus is not consistent with the Bayesian result. This suggests that the event is likely caused by the binary-lens binary-source model. 

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4. Analysis of the Full Spitzer Microlensing Sample. I. Dark Remnant Candidates and Gaia Predictions

   https://doi.org/10.3847/1538-4357/ad7bb1  

   Rybicki, Krzysztof A; Shvartzvald, Yossi; Yee, Jennifer C; Calchi_Novati, Sebastiano; Ofek, Eran O; Bond, Ian A; Beichman, Charles; Bryden, Geoff; Carey, Sean; Henderson, Calen; et al (November 2024, The Astrophysical Journal)

   Abstract In the pursuit of understanding the population of stellar remnants within the Milky Way, we analyze the sample of ∼950 microlensing events observed by the Spitzer Space Telescope between 2014 and 2019. In this study we focus on a subsample of nine microlensing events, selected based on their long timescales, small microlensing parallaxes, and joint observations by the Gaia mission, to increase the probability that the chosen lenses are massive and the mass is measurable. Among the selected events we identify lensing black holes and neutron star candidates, with potential confirmation through forthcoming release of the Gaia time-series astrometry in 2026. Utilizing Bayesian analysis and Galactic models, along with the Gaia Data Release 3 proper-motion data, four good candidates for dark remnants were identified: OGLE-2016-BLG-0293, OGLE-2018-BLG-0483, OGLE-2018-BLG-0662, and OGLE-2015-BLG-0149, with lens masses of ${3.0}_{-1.3}^{+1.8}{M}_{\odot }$, ${4.7}_{-2.1}^{+3.2}{M}_{\odot }$, ${3.15}_{-0.64}^{+0.66}{M}_{\odot }$and ${1.40}_{-0.55}^{+0.75}{M}_{\odot }$, respectively. Notably, the first two candidates are expected to exhibit astrometric microlensing signals detectable by Gaia, offering the prospect of validating the lens masses. The methodologies developed in this work will be applied to the full Spitzer microlensing sample, populating and analyzing the timescale (t_E) versus parallax (π_E) diagram to derive constraints on the population of lenses in general and massive remnants in particular. 

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5. The Scale of Stellar Yields: Implications of the Measured Mean Iron Yield of Core Collapse Supernovae

   https://doi.org/10.3847/1538-4357/ad6313  

   Weinberg, David H; Griffith, Emily J; Johnson, James W; Thompson, Todd A (September 2024, The Astrophysical Journal)

   Abstract The scale ofα-element yields is difficult to predict from theory because of uncertainties in massive star evolution, supernova physics, and black hole formation, and it is difficult to constrain empirically because the impact of higher yields can be compensated by greater metal loss in galactic winds. We use a recent measurement of the mean iron yield of core collapse supernovae (CCSN) by Rodriguez et al., ${\overline{y}}_{\mathrm{Fe}}^{\mathrm{cc}}=0.058\pm 0.007M_{\odot }$, to infer the scale ofα-element yields by assuming that the plateau of [α/Fe] abundance ratios observed in low-metallicity stars represents the yield ratio of CCSN. For a plateau at [α/Fe]_cc= 0.45, we find that the population-averaged yields of O and Mg are about equal to the solar abundance of these elements, $\log y_{\mathrm{O}}^{\mathrm{cc}}/Z_{\mathrm{O},\odot }=\log y_{\mathrm{Mg}}^{\mathrm{cc}}/Z_{\mathrm{Mg},\odot }=-0.01\pm 0.1$, where $y_{\mathrm{X}}^{\mathrm{cc}}$is the mass of element X produced by massive stars per unit mass of star formation. The inferred O and Fe yields agree with predictions of the Sukhbold et al. CCSN models assuming their Z9.6+N20 neutrino-driven engine, a scenario in which many progenitors withM< 40M_⊙implode to black holes rather than exploding. The yields are lower than assumed in many models of the galaxy mass–metallicity relation, reducing the level of outflows needed to match observed abundances. Our one-zone chemical evolution models with $\eta ={\dot{M}}_{\mathrm{out}}/{\dot{M}}_{*}\approx 0.6$evolve to solar metallicity at late times. By further requiring that models reach [α/Fe] ≈ 0 at late times, we infer a Hubble-time integrated Type Ia supernova rate of $1.1\times {10}^{-3}{M}_{\odot }^{-1}$, compatible with estimates from supernova surveys. 

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