More Like this

1. Measuring the Ellipticity of M87* Images

   https://doi.org/10.3847/1538-4357/ac9cd2  

   Tiede, Paul; Broderick, Avery E.; Palumbo, Daniel C.; Chael, Andrew (December 2022, The Astrophysical Journal)

   Abstract The Event Horizon Telescope (EHT) images of the supermassive black hole at the center of the galaxy M87 provided the first image of the accretion environment on horizon scales. General relativity (GR) predicts that the image of the shadow should be nearly circular given the inclination angle of the black hole M87*. A robust detection of ellipticity in image reconstructions of M87* could signal new gravitational physics on horizon scales. Here we analyze whether the imaging parameters used in EHT analyses are sensitive to ring ellipticity, and measure the constraints on the ellipticity of M87*. We find that the top set is unable to recover ellipticity. Even for simple geometric models, the true ellipticity is biased low, preferring circular rings. Therefore, to place a constraint on the ellipticity of M87*, we measure the ellipticity of 550 synthetic data sets produced from GRMHD simulations. We find that images with intrinsic axis ratios of 2:1 are consistent with the ellipticity seen from EHT image reconstructions. 

   more » « less
2. 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. 

   more » « less
3. Supermassive Black Hole Spin Constraints from Polarimetry in an Equatorial Disk Model

   https://doi.org/10.3847/2041-8213/ad9bb4  

   Palumbo, Daniel_C M (December 2024, The Astrophysical Journal Letters)

   Abstract The Event Horizon Telescope has released polarized images of the supermassive black holes Messier 87* (M87*) and Sagittarius A* accretion disks. As more images are produced, our understanding of the average polarized emission from near the event horizon improves. In this Letter, we use a semianalytic model for optically thin, equatorial emission near a Kerr black hole to study how spin constraints follow from measurements of the average polarization spiral pitch angle. We focus on the case of M87* and explore how the direct, weakly lensed image spiral is coupled to the strongly lensed indirect image spiral, and how a precise measurement of both provides a powerful spin tracer. We find a generic result that the spin twists the direct and indirect image polarization in opposite directions. Using a grid search over model parameters, we find a strong dependence of the resulting spin constraint on plasma properties near the horizon. Grid constraints suggest that, under reasonable assumptions for the accretion disk, a measurement of the direct and indirect image spiral pitch angles to ±5° yields a dimensionless spin amplitude measurement with uncertainty ${\sigma }_{\mid a_{*}\mid }\sim 0.25$for radially infalling models but otherwise provides only weak constraints; an error of 1^∘can reach ${\sigma }_{\mid a_{*}\mid }\sim 0.15$. We also find that a well-constrained rotation measure greatly improves spin measurements. Assuming that equatorial velocity and magnetic field are oppositely oriented, we find that the observed M87* polarization pattern favors models with strong radial velocity components, which are close to optimal for future spin measurements. 

   more » « less
4. Median Statistics Estimate of the Distance to M87

   https://doi.org/10.1088/1538-3873/ad220e  

   Rackers, Nicholas; Splawska, Sofia; Ratra, Bharat (February 2024, Publications of the Astronomical Society of the Pacific)

   Abstract de Grijs & Bono compiled 211 independent measurements of the distance to galaxy M87 in the Virgo cluster from 15 different tracers and reported 31.03 ± 0.14 mag as the arithmetic mean of a subset of this compilation as the best estimate of the distance. We compute three different central estimates—the arithmetic mean, weighted mean, and the median—and corresponding statistical uncertainty for the full data set as well as three sub-compilations. We find that for all three central estimates the error distributions show that the data sets are significantly non-Gaussian. As a result, we conclude that the median is the most reliable of the three central estimates, as median statistics do not assume Gaussianity. We use median statistics to determine the systematic error on the distance by analyzing the scatter in the 15 tracer subgroup distances. From the 211 distance measurements, we recommend a summary M87 distance modulus of ${31.08}_{-0.04}^{+0.05}$(statistical) ${}_{-0.06}^{+0.04}$(systematic) mag, or combining the two errors in quadrature ${31.08}_{-0.07}^{+0.06}$mag, rounded to 16.4 ± 0.5 Mpc, all at 68.27% significance. 

   more » « less
5. Constraining a Companion of the Galactic Center Black Hole Sgr A*

   https://doi.org/10.3847/1538-4357/ad09b3  

   Will, Clifford M; Naoz, Smadar; Hees, Aurélien; Tucker, Alexandria; Zhang, Eric; Do, Tuan; Ghez, Andrea (December 2023, The Astrophysical Journal)

   Abstract We use 23 yr of astrometric and radial velocity data on the orbit of the star S0-2 to constrain a hypothetical intermediate-mass black hole orbiting the massive black hole Sgr A* at the Galactic center. The data place upper limits on variations of the orientation of the stellar orbit at levels between 0.°02 and 0.°07 per year. We use a combination of analytic estimates and full numerical integrations of the orbit of S0-2 in the presence of a black hole binary. For a companion intermediate-mass black hole outside the orbit of S0-2 (1020 au), we find that a companion black hole with massm_cbetween 10³and 10⁵M_⊙is excluded, with a boundary behaving as $a_c\sim m_c^{1/3}$. For a companion witha_c< 1020 au, a black hole with mass between 10³and 10⁵M_⊙is excluded, with $a_c\sim m_c^{-1/2}$. These bounds arise from quadrupolar perturbations of the orbit of S0-2. Significantly stronger bounds on an inner companion arise from the fact that the location of S0-2 is measured relative to the bright emission of Sgr A* and that separation is perturbed by the “wobble” of Sgr A* about the center of mass between it and the companion. The result is a set of bounds as small as 400M_⊙at 200 au; the numerical simulations suggest a bound from these effects varying as $a_c\sim m_c^{-1}$. We compare and contrast our results with those from a recent analysis by the GRAVITY collaboration. 

   more » « less