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1. An Exceptional Dimming Event for a Massive, Cool Supergiant in M51

   https://doi.org/10.3847/1538-4357/ac626c  

   Jencson, Jacob E.; Sand, David J.; Andrews, Jennifer E.; Smith, Nathan; Pearson, Jeniveve; Strader, Jay; Valenti, Stefano; Beasor, Emma R.; Rothberg, Barry (May 2022, The Astrophysical Journal)

   Abstract We present the discovery of an exceptional dimming event in a cool supergiant star in the Local Volume spiral M51. The star, dubbed M51-DS1, was found as part of a Hubble Space Telescope (HST) search for failed supernovae (SNe). The supergiant, which is plausibly associated with a very young (≲6 Myr) stellar population, showed clear variability (amplitude ΔF814W≈ 0.7 mag) in numerous HST images obtained between 1995 and 2016, before suddenly dimming by >2 mag inF814Wsometime between late 2017 and mid-2019. In follow-up data from 2021, the star rebrightened, ruling out a failed supernova. Prior to its near-disappearance, the star was luminous and red (M_F814W≲ − 7.6 mag,F606W−F814W= 1.9–2.2 mag). Modeling of the pre-dimming spectral energy distribution of the star favors a highly reddened, very luminous ( $\log \left[L/L_{\odot }\right]=5.4$–5.7) star withT_eff≈ 3700–4700 K, indicative of a cool yellow or post-red supergiant (RSG) with an initial mass of ≈26–40M_⊙. However, the local interstellar extinction and circumstellar extinction are uncertain, and could be lower: the near-IR colors are consistent with an RSG, which would be cooler (T_eff≲ 3700 K) and slightly less luminous ( $\log \left[L/L_{\odot }\right]=5.2$–5.3), giving an inferred initial mass of ≈19–22M_⊙. In either case, the dimming may be explained by a rare episode of enhanced mass loss that temporarily obscures the star, potentially a more extreme counterpart to the 2019–2020 “Great Dimming” of Betelgeuse. Given the emerging evidence that massive evolved stars commonly exhibit variability that can mimic a disappearing star, our work highlights a substantial challenge in identifying true failed SNe. 

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2. Spectroscopic Confirmation of an Ultra-Massive Galaxy in a Protocluster at $z\sim 4.9$

   https://doi.org/10.33232/001c.120087  

   Urbano_Stawinski, Stephanie M; Cooper, M C; Forrest, Ben; Muzzin, Adam; Marchesini, Danilo; Wilson, Gillian; Gomez, Percy; McConachie, Ian; Marsan, Z Cemile; Annuziatella, Marianna; et al (June 2024, The Open Journal of Astrophysics)

   We present spectroscopic confirmation of an ultra-massive galaxy (UMG) with $log\left(M_{\star }/M_{\odot }\right)=10.98\pm 0.07$at $z_{\mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}}=4.8947$in the Extended Groth Strip (EGS), based on deep observations of Ly $\alpha$emission with Keck/DEIMOS. The ultra-massive galaxy (UMG-28740) is the most massive member in one of the most significant overdensities in the EGS, with four additional photometric members with $log\left(M_{\star }/M_{\odot }\right)>10.5$within $R_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{j}}\sim 1$cMpc. Spectral energy distribution (SED) fitting using a large suite of star formation histories and two sets of high-quality photometry from ground- and space-based facilities consistently estimates the mass of this object to be $log\left(M_{\star }/M_{\odot }\right)\sim 11$with a small standard deviation between measurements ( $\sigma =0.07$). While the best-fit SED models agree on stellar mass, we find discrepancies in the estimated star formation rate for UMG-28740, resulting in either a star-forming or quiescent system. $𝐽𝑊𝑆𝑇$/NIRCam photometry of UMG-28740 strongly favors a quiescent scenario, demonstrating the need for high-quality mid-IR observations. Assuming the galaxy to be quiescent, UMG-28740 formed the bulk of its stars at $z>10$and is quenching at $z\sim 8$, resulting in a high star formation efficiency at high redshift ( $ϵ\sim 0.2$at $z\sim 5$and $ϵ\gtrsim 1$at $z\gtrsim 8$). As the most massive galaxy in its protocluster environment, UMG-28740 is a unique example of the impossibly early galaxy problem. 

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3. Anomalies in Hadronic $B$ Decays

   https://doi.org/10.1103/PhysRevLett.133.211802  

   Berthiaume, Raphaël; Bhattacharya, Bhubanjyoti; Boumris, Rida; Jean, Alexandre; Kumbhakar, Suman; London, David (November 2024, Physical Review Letters)

   In this Letter, we perform fits to $B\to PP$decays, where $B=\{B^0,B^{+},B_s^0\}$and the pseudoscalar $P=\{\pi ,K\}$, under the assumption of flavor SU(3) symmetry [ ${\mathrm{SU}\left(3\right)}_F$]. Although the fits to $\mathrm{\Delta }S=0$or $\mathrm{\Delta }S=1$decays individually are good, the combined fit is very poor: there is a $3.6\sigma$disagreement with the ${\mathrm{SU}\left(3\right)}_F$limit of the standard model ( ${\mathrm{SM}}_{{\mathrm{SU}\left(3\right)}_{\mathrm{F}}}$). One can remove this discrepancy by adding ${\mathrm{SU}\left(3\right)}_F$-breaking effects, but 1000% ${\mathrm{SU}\left(3\right)}_F$breaking is required. The above results are rigorous, group theoretically—no dynamical assumptions have been made. When one adds an assumption motivated by QCD factorization, the discrepancy with the ${\mathrm{SM}}_{{\mathrm{SU}\left(3\right)}_{\mathrm{F}}}$grows to $4.4\sigma$. Published by the American Physical Society2024 

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4. A Luminous Red Supergiant and Dusty Long-period Variable Progenitor for SN 2023ixf

   https://doi.org/10.3847/2041-8213/ace618  

   Jencson, Jacob E.; Pearson, Jeniveve; Beasor, Emma R.; Lau, Ryan M.; Andrews, Jennifer E.; Bostroem, K. Azalee; Dong 董, Yize 一泽; Engesser, Michael; Gomez, Sebastian; Guolo, Muryel; et al (July 2023, The Astrophysical Journal Letters)

   Abstract We analyze pre-explosion near- and mid-infrared (IR) imaging of the site of SN 2023ixf in the nearby spiral galaxy M101 and characterize the candidate progenitor star. The star displays compelling evidence of variability with a possible period of ≈1000 days and an amplitude of Δm≈ 0.6 mag in extensive monitoring with the Spitzer Space Telescope since 2004, likely indicative of radial pulsations. Variability consistent with this period is also seen in the near-IRJandK_sbands between 2010 and 2023, up to just 10 days before the explosion. Beyond the periodic variability, we do not find evidence for any IR-bright pre-supernova outbursts in this time period. The IR brightness ( $M_{K_s}=-10.7$mag) and color (J−K_s= 1.6 mag) of the star suggest a luminous and dusty red supergiant. Modeling of the phase-averaged spectral energy distribution (SED) yields constraints on the stellar temperature ( $T_{\mathrm{eff}}={3500}_{-1400}^{+800}$K) and luminosity ( $\log L/L_{\odot }=5.1\pm 0.2$). This places the candidate among the most luminous Type II supernova progenitors with direct imaging constraints, with the caveat that many of these rely only on optical measurements. Comparison with stellar evolution models gives an initial mass ofM_init= 17 ± 4M_⊙. We estimate the pre-supernova mass-loss rate of the star between 3 and 19 yr before explosion from the SED modeling at $\dot{M}\approx 3\times {10}^{-5}$to 3 × 10⁻⁴M_⊙yr⁻¹for an assumed wind velocity ofv_w= 10 km s⁻¹, perhaps pointing to enhanced mass loss in a pulsation-driven wind. 

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5. Anomalies in hadronic $B$ decays: An update

   https://doi.org/10.1103/5jp1-7cfw  

   Bhattacharya, Bhubanjyoti; Bouchard, Marianne; Hudy, Luke; Jean, Alexandre; London, David; MacKenzie, Christopher (September 2025, Physical Review D)

   Recently, $B\to PP$decays ( $B=\{B^0,B^{+},B_s^0\}$, $P=\{\pi ,K\}$) were analyzed under the assumption of flavor SU(3) symmetry ( ${\mathrm{SU}\left(3\right)}_F$). Although the individual fits to $\mathrm{\Delta }S=0$or $\mathrm{\Delta }S=1$decays are good, it was found that the combined fit is very poor: there is a $3.6\sigma$disagreement with the ${\mathrm{SU}\left(3\right)}_F$limit of the standard model ( ${\mathrm{SM}}_{{\mathrm{SU}\left(3\right)}_F}$). One can remove this discrepancy by adding ${\mathrm{SU}\left(3\right)}_F$-breaking effects, but 1000% ${\mathrm{SU}\left(3\right)}_F$breaking is required. In this paper, we extend this analysis to include decays in which there is an $\eta$and/or ${\eta }^{\prime }$meson in the final state. We now find that the combined fit exhibits a $4.1\sigma$discrepancy with the ${\mathrm{SM}}_{{\mathrm{SU}\left(3\right)}_F}$, and 1000% ${\mathrm{SU}\left(3\right)}_F$-breaking effects are still required to explain the data. These results are rigorous, group-theoretically—no theoretical assumptions have been made. But when one adds some theoretical input motivated by QCD factorization, the discrepancy with the ${\mathrm{SM}}_{{\mathrm{SU}\left(3\right)}_F}$grows to $4.9\sigma$. 

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