Supermassive Research Articles

A Comparison of the X-Ray Polarimetric Properties of Stellar and Supermassive Black Holes

X-ray polarization provides a new way to probe accretion geometry in black hole systems. If the accretion geometry of black holes is similar regardless of mass, we should expect the same to be true of their polarization properties. We compare the polarimetric properties of all nonblazar black holes observed with the Imaging X-ray Polarimetry Explorer. We find that their polarization properties are very similar, particularly in the hard state, where the corona dominates. This tentatively supports the idea that stellar and supermassive black holes share a common coronal geometry.

Supermassive black hole formation via collisions in black hole clusters

More than 300 supermassive black holes have been detected at redshifts larger than six, and they are abundant in the centers of local galaxies. Their formation mechanisms, however, are still rather unconstrained. A possible origin of these supermassive black holes could be mergers in dense black hole clusters, forming as a result of mass segregation within nuclear star clusters at the center of galaxies. In this study, we present the first systematic investigation of the evolution of such black hole clusters in which the effect of an external potential is taken into account. Such a potential could be the result of gas inflows into the central region; for example, as a result of galaxy mergers. We show here that the efficiency of the formation of a massive central object is mostly regulated by the ratio of cluster velocity dispersion divided by the speed of light, potentially reaching efficiencies of 0.05–0.08 in realistic systems. Our results show that this scenario is potentially feasible and may provide black hole seeds of at least 103 M⊙. We conclude that the formation of seed black holes via this channel should be taken into account in statistical assessments of the black hole population.

The Primary Flare Following a Stellar Collision in a Galactic Nucleus

High-velocity stellar collisions near supermassive black holes may result in a complete disruption of the stars. The initial disruption can have energies on par with supernovae and power a very fast transient. In this work, we examine the primary flare that follows the initial transient, which arises when streams of gas from the disrupted stars travel around the central black hole and collide with each other on the antipodal side with respect to the original collision. We present a simple analytic estimate for the properties of the flare, which depends on the distance of the collision from the central black hole and on the center of mass velocity of the colliding stars. We also present the first-of-their-kind radiation-hydrodynamics simulations of a few examples of stellar collisions and postcollision flow of the ejected gas and calculate the expected bolometric light curves. We find that such postcollision flares are expected to be similar to flares that arise in tidal disruptions events of single stars.

Radio Scrutiny of the X-Ray-weak Tail of Low-mass Active Galactic Nuclei: A Novel Signature of High-Eddington Accretion?

The supermassive black holes (M BH ∼ 106–1010 M ⊙) that power luminous active galactic nuclei (AGNs), i.e., quasars, generally show a correlation between thermal disk emission in the ultraviolet (UV) and coronal emission in hard X-rays. In contrast, some “massive” black holes (mBHs; M BH ∼ 105–106 M ⊙) in low-mass galaxies present curious X-ray properties with coronal radiative output up to 100× weaker than expected. To examine this issue, we present a pilot study incorporating Very Large Array radio observations of a sample of 18 high-accretion-rate (Eddington ratios L bol/L Edd > 0.1), mBH-powered AGNs (M BH ∼ 106 M ⊙) with Chandra X-ray coverage. Empirical correlations previously revealed in samples of radio-quiet, high-Eddington AGNs indicate that the radio–X-ray luminosity ratio, L R/L X, is approximately constant. Through multiwavelength analysis, we instead find that the X-ray-weaker mBHs in our sample tend toward larger values of L R/L X even though they remain radio-quiet per their optical–UV properties. This trend results in a tentative but highly intriguing correlation between L R/L X and X-ray weakness, which we argue is consistent with a scenario in which X-rays may be preferentially obscured from our line of sight by a “slim” accretion disk. We compare this observation to weak emission-line quasars (AGNs with exceptionally weak broad-line emission and a significant X-ray-weak fraction) and conclude by suggesting that our results may offer a new observational signature for finding high-accretion-rate AGNs.

Accretion onto a Supermassive Black Hole Binary before Merger

While supermassive binary black holes (SMBBHs) inspiral toward merger they may also accrete matter from a surrounding disk. To study the dynamics of this system requires simultaneously describing the evolving spacetime and the magnetized plasma. We present the first relativistic calculation simulating two equal-mass, nonspinning black holes as they inspiral from a 20 M (G = c = 1) initial separation almost to merger. Our results imply important observational consequences: for instance, the accretion rate Ṁ onto the black holes first decreases and then plateaus, dropping by only a factor of ∼3 despite the rapid inspiral. An estimated bolometric light curve follows the same profile, suggesting some merging SMBBHs may be significantly luminous past the predicted circumbinary disk decoupling. The minidisks are nonstandard: Reynolds, not Maxwell, stresses dominate, and they oscillate between two states. In one part of the cycle, “sloshing” streams transfer mass between minidisks, carrying kinetic energy at a rate sometimes as high as the peak minidisk bolometric luminosity. We also discover that episodic accretion drives time-varying minidisk tilts. These complex dynamics all contribute to unique cyclical behavior in the light curves of late-time inspiraling SMBBHs. The poloidal magnetic flux on the black holes is roughly constant at a dimensionless level ϕ ∼ 2–3, but doubles just before merger; for significant black hole spin, this flux predicts powerful jets with variability driven by binary dynamics, another potentially unique electromagnetic signature. This simulation is the first to employ our multipatch infrastructure PatchworkMHD, decreasing the computational expense to ∼3% of conventional single-grid methods’ cost.

Core Formation by Binary Scouring and Gravitational Wave Recoil in Massive Elliptical Galaxies

Scouring by supermassive black hole (SMBH) binaries is the most accepted mechanism for the formation of the cores seen in giant elliptical galaxies. However, an additional mechanism is required to explain the largest observed cores. Gravitational-wave (GW) recoil is expected to trigger further growth of the core, as subsequent heating from dynamical friction of the merged SMBH removes stars from the central regions. We model core formation in massive elliptical galaxies from both binary scouring and heating by GW recoil and examine their unique signatures. We aim to determine whether the nature of cores in 3D space density can be attributed uniquely to either process and whether the magnitude of the kick can be inferred. We perform N-body simulations of galactic mergers of multicomponent galaxies, based on the observed parameters of four massive elliptical galaxies with cores >0.5 kpc. After binary scouring and hardening, the merged SMBH remnant is given a range of GW recoil kicks with 0.5–0.9 of the escape speed of the galaxy. We find that binary scouring alone can form the cores of NGC 1600 and A2147-BCG, which are <1.3 kpc in size. However, the >2 kpc cores in NGC 6166 and A2261-BCG require heating from GW recoil kicks of <0.5 of the galaxy escape speed. A unique feature of GW recoil heating is flatter cores in surface brightness, corresponding to truly flat cores in 3D space density. It also preferentially removes stars on low angular momentum orbits from the galactic nucleus.

Gravitational lensing of spherically symmetric black holes in dark matter halos

The gravitational lensing of supermassive black holes surrounded by dark matter halo has attracted a great number of interests in recent years. However, many studies employed simplified dark matter density models, which makes it very hard to give a precise prediction on the dark matter effects in real astrophysical galaxies. In this work, to more accurately describe the distribution of dark matter in real astrophysical galaxies, we study the gravitational lensing of black holes in astrophysical dark matter halo models (Beta, Burkert, Brownstein, and Moore). The deflection angle is obtained using a generalized Gibbons-Werner approach. The visual angular positions and the Einstein rings are also calculated by adopting the gravitational lens equation. Specifically, we choose the supermassive black holes in Milky Way Galaxy, Andromeda galaxy (M31), Virgo galaxy (M87), and ESO138-G014 galaxy as examples, including the corresponding fitted value of dark matter halos. The results suggest that the dark matter halo described by the Beta model has non-negligible influences on the gravitational deflection angle and gravitational lensing observations. However, the Burkert, Brownstein, and Moore models have relatively small influences on angular position of images and the Einstein ring.

Gravitational collapse at low to moderate Mach numbers: The relationship between star formation efficiency and the fraction of mass in the massive object

The formation of massive objects via gravitational collapse is relevant both for explaining the origin of the first supermassive black holes and in the context of massive star formation. Here, we analyze simulations of the formation of massive objects pursued by different groups and in various environments, concerning the formation of supermassive black holes, primordial stars, as well as present-day massive stars. We focus here particularly on the regime of small virial parameters, that is, low ratios of the initial kinetic to gravitational energy, low to moderate Mach numbers, and the phase before feedback is very efficient. We compare the outcomes of collapse under different conditions using dimensionless parameters, particularly the star formation efficiency є*, the fraction ƒ* of mass in the most massive object relative to the total stellar mass, and the fraction ƒtot of mass of the most massive object as a function of the total mass. We find that in all simulations analyzed here, ƒtot increases as a function of є*, although the steepness of the increase depends on the environment. The relation between ƒ* and є* is found to be more complex and also strongly depends on the number of protostars present at the beginning of the simulations. We show that a collision parameter, estimated as the ratio of the system size divided by the typical collision length, allows us to approximately characterize whether collisions are important. A high collision parameter implies a steeper increase in the relation between ƒtot and є*. We analyze the statistical correlation between the dimensionless quantities using the Spearman coefficient and further confirm via a machine learning analysis that good predictions of ƒ* can be obtained from є* together with a rough estimate of the collision parameter. This suggests that a good estimate of the mass of the most massive object can be obtained once the maximum efficiency for a given environment is known and an estimate for the collision parameter has been determined.

Two Radio Cores in GPS J1543-0757: A New Dual Supermassive Black Hole System?

We report on the discovery of a dual supermassive black hole system in the radio galaxy J1543−0757, with a projected separation between the two black holes of ∼46 mas. The result is based on recent multifrequency observations using the Very Long Baseline Array and European VLBI Network, which reveal two compact, variable, flat-spectrum, active nuclei within the elliptical host galaxy of J1543−0757. Multiepoch observations from the Very Long Baseline Array also provide constraints on the spectral index and proper motions of all components. The flat spectra of both N and S at both frequencies strongly support the hypothesis that these radio components are associated with two separate, accreting supermassive black holes. The two nuclei appear stationary, while the jets emanating from the weaker of the two nuclei appear to move out and terminate in bright hotspots. The discovery of this system has implications for the number of close dual black holes that might be sources of gravitational radiation.

Late-time X-Ray Observations of the Jetted Tidal Disruption Event AT2022cmc: The Relativistic Jet Shuts Off

The tidal disruption event (TDE) AT2022cmc represents the fourth known example of a relativistic jet produced by the tidal disruption of a stray star, providing a unique probe of the formation and evolution of relativistic jets in otherwise dormant supermassive black holes (SMBHs). Here we present deep, late-time Chandra observations of AT2022cmc extending to t obs ≈ 400 days after disruption. Our observations reveal a sudden decrease in the X-ray brightness by a factor of ≳14 over a factor of ≈2.3 in time, and a deviation from the earlier power-law decline with a steepening α ≳ 3.2 (F X ∝ t −α ), steeper than expected for a jet break, and pointing to the cessation of jet activity at t obs ≈ 215 days. Such a transition has been observed in two previous TDEs (Swift J1644+57 and Swift J2058+05). From the X-ray luminosity and the timescale of jet shut-off, we parameterize the mass of the SMBH in terms of unknown jet efficiency and accreted mass fraction parameters. Motivated by the disk–jet connection in active galactic nuclei, we favor black hole masses ≲105 M ⊙ (where the jet and disk luminosities are comparable), and disfavor larger black holes (in which extremely powerful jets are required to outshine their accretion disks). We additionally estimate a total accreted mass of ≈0.1 M ⊙. Applying the same formalism to Swift J1644+57 and Swift J2058+05, we favor comparable black hole masses for these TDEs of ≲ a few × 105 M ⊙, and suggest that jetted TDEs may preferentially form from lower-mass black holes when compared to nonrelativistic events, owing to generally lower jet and higher disk efficiencies at higher black hole masses.

Prospects of Detecting a Jet in Sagittarius A* with Very-long-baseline Interferometry

Event Horizon Telescope (EHT) images of the horizon-scale emission around the Galactic center supermassive black hole Sagittarius A* (Sgr A*) favor accretion flow models with a jet component. However, this jet has not been conclusively detected. Using the “best-bet” models of Sgr A* from the EHT Collaboration, we assess whether this nondetection is expected for current facilities and explore the prospects of detecting a jet with very-long-baseline interferometry (VLBI) at four frequencies: 86, 115, 230, and 345 GHz. We produce synthetic image reconstructions for current and next-generation VLBI arrays at these frequencies that include the effects of interstellar scattering, optical depth, and time variability. We find that no existing VLBI arrays are expected to detect the jet in these best-bet models, consistent with observations to date. We show that next-generation VLBI arrays at 86 and 115 GHz—in particular, the EHT after upgrades through the ngEHT program and the ngVLA—successfully capture the jet in our tests due to improvements in instrument sensitivity and (u, v) coverage at spatial scales critical to jet detection. These results highlight the potential of enhanced VLBI capabilities in the coming decade to reveal the crucial properties of Sgr A* and its interaction with the Galactic center environment.

A Magnetized Strongly Turbulent Corona as the Source of Neutrinos from NGC 1068

The cores of active galactic nuclei are potential accelerators of 10–100 TeV cosmic rays, in turn producing high-energy neutrinos. This picture was confirmed by the compelling evidence of a TeV neutrino signal from the nearby active galaxy NGC 1068, leaving open the question of what is the site and mechanism of cosmic-ray acceleration. One candidate is the magnetized turbulence surrounding the central supermassive black hole. Recent particle-in-cell simulations of magnetized turbulence indicate that stochastic cosmic-ray acceleration is nonresonant, in contrast to the assumptions of previous studies. We show that this has important consequences on a self-consistent theory of neutrino production in the corona, leading to a more rapid cosmic-ray acceleration than previously considered. The turbulent magnetic-field fluctuations needed to explain the neutrino signal are consistent with a magnetically powered corona. We find that strong turbulence, with turbulent magnetic energy density higher than 1% of the rest-mass energy density, naturally explains the normalization of the IceCube neutrino flux, in addition to the neutrino spectral shape. Only a fraction of the protons in the corona, which can be directly inferred from the neutrino signal, are accelerated to high energies. Thus, in this framework, the neutrino signal from NGC 1068 provides a testbed for particle acceleration in magnetized turbulence.

Molecular Distribution in the Central Region of M87

The central region of M87 has been observed by the Atacama Large Millimeter/submillimeter Array (ALMA) several times to resolve its molecular cloud distribution. We present the ALMA CO(1–0), CO(2–1), and CO(3–2) observations of the M87 circumnuclear region. The CO(1–0) shows emission as well as molecular absorption features toward its nucleus, indicating the existence of cold molecular clouds/gas. ALMA imaging of the CO(1–0) observations show the distribution of molecular clouds toward the nucleus of M87 with a radius of ∼105 pc. The clouds seen in the CO(1–0) are moving with very high velocity and have an apparent motion in the range of −1000 to 3600 km s−1 relative to the central supermassive black hole, which has a systemic velocity of ∼1266 km s−1. The molecular gas mass was estimated to be about 1.08 ± 0.64 × 107 M ⊙ in the central 210 pc of M87. We calculated the optical depths using the absorption lines of the CO(1–0) and CO(2–1). The excitation temperature was estimated to be ∼7.133 ± 0.03 K using the optical depth ratio of the CO(2-1) to CO(1-0). We also found the line-of-sight column density to be ∼2.25 × 1015 cm−2, which corresponds to a hydrogen column density of ∼0.28 × 1020 cm−2.

Multistructured Accretion Flow of Sgr A*. I. Examination of a Radiatively Inefficient Accretion Flow Model

The extreme low-luminosity supermassive black hole Sgr A* provides a unique laboratory in which to test models of radiatively inefficient accretion flows (RIAFs). Previous fits to the quiescent Chandra ACIS-S spectrum found that a RIAF model with an equal inflow–outflow balance works well. In this work, we apply the RIAF model to the Chandra HETG-S spectrum obtained through the Chandra X-ray Visionary Program, which displays features suggestive of temperature and velocity structures within the plasma. A comprehensive forward model analysis accounting for the accretion flow geometry and HETG-S instrumental effects is required for a full interpretation of the quiescent Chandra HETG-S spectrum. We present a RIAF model that takes these effects into account. Our fits to the high-resolution grating spectrum indicate an inflow balanced by an outflow (s ∼ 1) alongside a temperature profile that appears shallower than what would be expected from a gravitational potential following 1/r. The data require that the abundance of iron relative to solar is Z Fe < 0.32 Z ⊙ (90% credible interval), much lower than the 2 Z ⊙ metallicity measured in nearby late-type giants. While future missions like NewAthena will provide higher spectral resolution, source separation will continue to be a problem. Leveraging Chandra’s unparalleled spatial resolution, which is not expected to be surpassed for decades, remains essential for detailed investigations of the densely populated Galactic center in X-rays.

CIRCLEZ : Reliable photometric redshifts for active galactic nuclei computed solely using photometry from Legacy Survey Imaging for DESI

Context. Photometric redshifts for galaxies hosting an accreting supermassive black hole in their center, known as active galactic nuclei (AGNs), are notoriously challenging. At present, they are most optimally computed via spectral energy distribution (SED) fittings, assuming that deep photometry for many wavelengths is available. However, for AGNs detected from all-sky surveys, the photometry is limited and provided by a range of instruments and studies. This makes the task of homogenizing the data challenging, presenting a dramatic drawback for the millions of AGNs that wide surveys such as SRG/eROSITA are poised to detect. Aims. This work aims to compute reliable photometric redshifts for X-ray-detected AGNs using only one dataset that covers a large area: the tenth data release of the Imaging Legacy Survey (LS10) for DESI. LS10 provides deep grizW1-W4 forced photometry within various apertures over the footprint of the eROSITA-DE survey, which avoids issues related to the cross-calibration of surveys. Methods. We present the results from CIRCLEZ, a machine-learning algorithm based on a fully connected neural network. CIRCLEZ is built on a training sample of 14 000 X-ray-detected AGNs and utilizes multi-aperture photometry, mapping the light distribution of the sources. Results. The accuracy (σNMAD) and the fraction of outliers (η) reached in a test sample of 2913 AGNs are equal to 0.067 and 11.6%, respectively. The results are comparable to (or even better than) what was previously obtained for the same field, but with much less effort in this instance. We further tested the stability of the results by computing the photometric redshifts for the sources detected in CSC2 and Chandra-COSMOS Legacy, reaching a comparable accuracy as in eFEDS when limiting the magnitude of the counterparts to the depth of LS10. Conclusions. The method can be applied to fainter samples of AGNs using deeper optical data from future surveys (for example, LSST, Euclid), granting LS10-like information on the light distribution beyond the morphological type. Along with this paper, we have released an updated version of the photometric redshifts (including errors and probability distribution functions) for eROSITA/eFEDS.

Prospects for Revealing Intermediate-mass Black Holes in NGC 1399 Using SKA

This study investigates the detectability of intermediate-mass black holes (IMBHs) within the mass range 102 M ⊙ ≤ M BH ≤ 105 M ⊙ in the globular star clusters of NGC 1399 at a frequency of 300.00 MHz. Employing the theoretical Bondi accretion model and the empirical fundamental plane (FP) of black hole accretion, we estimate IMBH masses based on bolometric luminosity and X-ray/radio luminosities, respectively. By simulating a 3 hr observation of 77 globular cluster (GC) candidates using the Square Kilometre Array, we identify radio detection benchmarks indicative of accretion onto IMBHs. Our results show that IMBHs inside the globular star clusters located in NGC 1399 are indeed detectable, with the Bondi accretion model providing IMBH mass estimates ranging from 2.93 × 103.0±0.39 M ⊙ to 7.43 × 104.0±0.39 M ⊙ and the empirical FP relation suggesting IMBH mass estimation with 3.41 × 105.0±0.96 M ⊙. These findings highlight the presence and detectability of IMBHs in GCs, offering insights into their role as precursors to supermassive black holes and enriching our understanding of black hole formation and evolution in astrophysical environments.

A Gamma-Ray Flare from TXS 1508+572: Characterizing the Jet of a z = 4.31 Blazar in the Early Universe

Blazars can be detected from very large distances due to their high luminosity. However, the detection of γ-ray emission of blazars beyond z = 3 has only been confirmed for a small number of sources. Such observations probe the growth of supermassive black holes close to the peak of star formation in the history of galaxy evolution. As a result from a continuous monitoring of a sample of 80 z > 3 blazars with the Fermi Large Area Telescope (Fermi-LAT), we present the first detection of a γ-ray flare from the z = 4.31 blazar TXS 1508+572. This source showed high γ-ray activity from 2022 February to August, reaching a peak luminosity comparable to the most luminous flares ever detected with Fermi-LAT. We conducted a multiwavelength observing campaign involving XMM-Newton, the Neil Gehrels Swift Observatory, the Effelsberg 100 m radio telescope, and the Very Long Baseline Array. In addition, we make use of the monitoring programs by the Zwicky Transient Facility and the Near-Earth Object Wide-field Infrared Survey Explorer at optical and infrared wavelengths, respectively. We find that the source is particularly variable in the infrared band on daily timescales. The spectral energy distribution collected during our campaign is well described by a one-zone leptonic model, with the γ-ray flare originating from an increase of external Compton emission as a result of a fresh injection of accelerated electrons.

EIGER. VI. The Correlation Function, Host Halo Mass, and Duty Cycle of Luminous Quasars at z ≳ 6

We expect luminous (M 1450 ≲ −26.5) high-redshift quasars to trace the highest-density peaks in the early Universe. Here, we present observations of four z ≳ 6 quasar fields using JWST/NIRCam in the imaging and wide-field slitless spectroscopy mode and report a wide range in the number of detected [O iii]-emitting galaxies in the quasars’ environments, ranging between a density enhancement of δ ≈ 65 within a 2 cMpc radius—one of the largest protoclusters during the Epoch of Reionization discovered to date—to a density contrast consistent with zero, indicating the presence of a UV-luminous quasar in a region comparable to the average density of the Universe. By measuring the two-point cross-correlation function of quasars and their surrounding galaxies, as well as the galaxy autocorrelation function, we infer a correlation length of quasars at 〈z〉 = 6.25 of r0QQ=22.0−2.9+3.0cMpch−1 , while we obtain a correlation length of the [O iii]-emitting galaxies of r0GG=4.1±0.3cMpch−1 . By comparing the correlation functions to dark-matter-only simulations we estimate the minimum mass of the quasars’ host dark matter halos to be log10(Mhalo,min/M⊙)=12.43−0.15+0.13 (and log10(Mhalo,min[OIII]/M⊙)=10.56−0.03+0.05 for the [O iii] emitters), indicating that (a) luminous quasars do not necessarily reside within the most overdense regions in the early Universe, and that (b) the UV-luminous duty cycle of quasar activity at these redshifts is f duty ≪ 1. Such short quasar activity timescales challenge our understanding of early supermassive black hole growth and provide evidence for highly dust-obscured growth phases or episodic, radiatively inefficient accretion rates.

The role of active galactic nucleus feedback on the evolution of dwarf galaxies from cosmological simulations

Aims. Recent observational studies suggest that feedback from active galactic nuclei (AGNs) may play an important role in the formation and evolution of dwarf galaxies, an issue that has received little attention from a theoretical perspective. Methods. We investigated this using two sets of 12 cosmological magnetohydrodynamic simulations of the formation of dwarf galaxies (108.3M⊙ ≤ M* ≤ 109.8M⊙): one set using a version of the AURIGA galaxy formation physics model including AGN feedback and a parallel set with AGN feedback turned off. Results. We show that the full-physics AGN runs satisfactorily reproduce several scaling relations, including the black-hole-to-stellar mass (MBH-M⋆), the black-hole-to-sigma (MBH-σ⋆), and the baryonic Tully-Fisher relation. We find that the global star formation (SF) of galaxies run with an AGN is reduced compared to the one in which the AGN has been turned off, suggesting that AGN feedback is a viable way of suppressing SF in dwarf galaxies, even though none of our galaxies is completely quenched by z = 0. Furthermore, we find a tight correlation between the median SF rates and the MBH/M⋆ ratio in our simulated dwarfs. Star formation is suppressed due to gas heating in the vicinity of the AGN: less HI gas is available in AGN runs, though the total amount of gas is preserved across the two settings within each galaxy. This indicates that the main effect of AGN feedback in our dwarfs is to heat up and push the gas away from the galaxy’s centre rather than expelling it completely. Finally, we show that the two galaxies harbouring the largest supermassive black holes have suffered a considerable (up to ∼65%) reduction in their central dark matter density, pinpointing the role of AGNs in determining the final dark matter mass distribution within dwarf galaxies. This pilot paper highlights the importance of modelling AGN feedback at the lowest mass scales and the impact this can have on dwarf galaxy evolution.

Multistructured Accretion Flow of Sgr A*. II. Signatures of a Cool Accretion Disk in Hydrodynamic Simulations of Stellar Winds

Hydrodynamic simulations of the stellar winds from Wolf–Rayet stars within the Galactic center can provide predictions for the X-ray spectrum of the supermassive black hole Sgr A*. Herein, we present results from updated smooth particle hydrodynamics simulations, building on the architecture of Cuadra et al. and Russell et al., and find that a “cold” (104 K) gas disk forms around Sgr A* with a simulation runtime of 3500 yr. This result is consistent with previous grid-based simulations, demonstrating that a cold disk can form regardless of numerical method. We examine the plasma scenarios arising from an environment with and without this cold disk, by generating synthetic spectra for comparison to the quiescent Fe Kα Sgr A* spectrum from Chandra HETGS, taken through the Chandra X-ray Visionary Program. We find that current and future X-ray missions are unlikely to distinguish between the kinematic signatures in the plasma in these two scenarios. Nonetheless, the stellar wind plasma model presents a good fit to the dispersed Chandra spectra within 1.″5 of Sgr A*. We compare our results to the radiatively inefficient accretion flow (RIAF) model fit to the HETGS spectrum presented in Paper I and find that the Bayesian model evidence does not strongly favor either model. With 9″ angular resolution and high spectral resolution of the X-IFU, NewAthena will offer a clearer differentiation between the RIAF plasma model and hydrodynamic simulations, but only a future X-ray mission with arcsecond resolution will significantly advance our understanding of Sgr A*’s accretion flow in X-rays.