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arxiv: 1906.11242 · v1 · pith:QQ34FNMOnew · submitted 2019-06-26 · 🌌 astro-ph.GA · astro-ph.HE· gr-qc

First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring

The Event Horizon Telescope Collaboration This is my paper

Pith reviewed 2026-05-25 15:18 UTC · model grok-4.3

classification 🌌 astro-ph.GA astro-ph.HEgr-qc
keywords M87black hole shadowEvent Horizon TelescopeKerr black holeGRMHD simulationsasymmetric ringjet powergeneral relativity
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The pith

The asymmetric ring in M87 is the shadow of a spinning Kerr black hole as predicted by general relativity.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper builds a library of models from general relativistic magnetohydrodynamic simulations and produces synthetic images via ray tracing. These are compared to the Event Horizon Telescope data showing an asymmetric ring in M87. The comparison shows the ring is consistent with lensing of emission from hot plasma near the event horizon of a spinning black hole. Non-spinning models fail to generate jets as powerful as observed, while spinning ones extract energy from the black hole spin to power the jet. This alignment implies the spin points away from Earth and sets expectations for stable features in future images.

Core claim

The observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87's large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. In models that do produce a sufficiently powerful jet, the jet is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process.

What carries the argument

Library of GRMHD simulations and general relativistic ray-traced synthetic images compared to observed visibilities to test the Kerr black hole shadow.

If this is right

  • The ring radius and asymmetry are expected to remain stable in future EHT observations.
  • If aligned with the large-scale jet, the black hole spin vector points away from Earth.
  • The jet is powered by extraction of black hole spin energy.
  • Alternatives to a black hole can be tested with existing polarization data and simultaneous multi-wavelength observations.
  • Data at 230 and 345 GHz will provide new tests of the GRMHD models.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Spin energy extraction appears necessary to explain powerful jets in systems like M87.
  • Matching EHT data to simulation libraries could measure spins for other supermassive black holes.
  • The observed spin-jet alignment may constrain theories of how jets are launched and how black holes grow with their galaxies.
  • Polarization measurements could distinguish plasma conditions near the horizon beyond what the total intensity image shows.

Load-bearing premise

The library of GRMHD simulations is sufficiently complete and representative that non-spinning cases can be ruled out for lacking sufficiently powerful jets.

What would settle it

A future observation of a ring asymmetry inconsistent with the spin direction expected from jet alignment, or detection of a powerful jet from a non-spinning model.

Figures

Figures reproduced from arXiv: 1906.11242 by The Event Horizon Telescope Collaboration.

Figure 1
Figure 1. Figure 1: is Tb pk , ~´6 10 K9 , which is consistent with past EHT mm-VLBI measurements at 230 GHz (Doeleman et al. 2012; Akiyama et al. 2015), and GMVA 3 mm-VLBI measurements of the core region (Kim et al. 2018). Expressed in electron rest-mass (me) units, b pk b pk e , B, k T mc 1 Q º ()2  , where kB is Boltzmann’s constant. The true peak brightness temperature of the source is higher if the ring is unresolved by… view at source ↗
Figure 2
Figure 2. Figure 2: Time-averaged 1.3 mm images generated by five SANE GRMHD simulations with varying spin (a 0.94 * =- to a 0.97 * =+ from left to right) and Rhigh (Rhigh = 1 to Rhigh = 160 from top to bottom; increasing Rhigh corresponds to decreasing electron temperature). The colormap is linear. All models are imaged at i = 163°. The jet that is approaching Earth is on the right (west) in all the images. The black hole sp… view at source ↗
Figure 3
Figure 3. Figure 3: Same as in [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Binned location of the point of origin for all photons that make up an image, summed over azimuth, and averaged over all snapshots from the simulation. The colormap is linear. The event horizon is indicated by the solid white semicircle and the black hole spin axis is along the figure vertical axis. This set of four images shows MAD and SANE models with Rhigh = 10 and 160, all with a 0.94 * = . The region … view at source ↗
Figure 5
Figure 5. Figure 5: Illustration of the effect of black hole and disk angular momentum on ring asymmetry. The asymmetry is produced primarily by Doppler beaming: the bright region corresponds to the approaching side. In GRMHD models that fit the data comparatively well, the asymmetry arises in emission generated in the funnel wall. The sense of rotation of both the jet and funnel wall are controlled by the black hole spin. If… view at source ↗
Figure 6
Figure 6. Figure 6: Single frame from the accompanying animation. This shows the visibility amplitudes (top), closure phases plotted by Euclidean distance in 6D space (middle), and associated model images at full resolution (lower left) and convolved with the EHT2017 beam (lower right). Data from 2017 April 6 high-band are also shown in the top two plots. The video shows frames 1 through 100 and has a duration of 10 s. (An an… view at source ↗
Figure 7
Figure 7. Figure 7: Distribution of M/D obtained by fitting Image Library snapshots to the 2017 April 6 data, in mas, measured independently using the (left panel) THEMIS and (right panel) GENA pipelines with qualitatively similar results. Smooth lines were drawn with a Gaussian kernel density estimator. The three lines show the best-fit 1% within each model (solid); the best-fit 10% within each model (dashed); and all model … view at source ↗
Figure 8
Figure 8. Figure 8: Distributions of M/D and black hole mass with D = 16.9 Mpc reconstructed from the best-fit 10% of images for MAD (left panel) and SANE (right panel) models (i = 17° for a 0 * £ and 163° for a 0 * > ) with different Rhigh and a*, from the THEMIS (dark red, left), and GENA (dark green, right) pipelines. The white dot and vertical black bar correspond, respectively, to the median and region between the 25th a… view at source ↗
Figure 9
Figure 9. Figure 9: Top: distribution of best-fit PA (in degree) scored by the THEMIS (left) and GENA (right) pipelines for models with black hole spin vector pointing away from Earth (i > 90° for a 0 * > or i < 90° for a 0 * < ). Bottom: images with black hole spin vector pointing toward Earth (i < 90° for a 0 * > or i > 90° for a 0 * < ). Smooth lines were drawn with a wrapped Gaussian kernel density estimator. The three li… view at source ↗
Figure 10
Figure 10. Figure 10: Ratio Pjet/Pout as a function of the outflow velocity cutoff parameter cut bg . Evidently, as the cut is decreased, so that the maximum asymptotic speed of the jet flow is decreased, an increasing fraction of Pout is classified as Pjet. Our nominal cutoff is bg = 1, which corresponds to vc 12 r b º= . Using this definition, Pjet for a 0 * = models is small because the energy flux in the relativistic outfl… view at source ↗
Figure 11
Figure 11. Figure 11: Decomposition of time-averaged 1.3 mm images from [PITH_FULL_IMAGE:figures/full_fig_p025_11.png] view at source ↗
read the original abstract

The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87's large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The paper analyzes the asymmetric ring in the 2017 EHT 1.3 mm image of M87 by constructing a library of GRMHD simulations and general-relativistic ray-traced images. It reports that the observed ring morphology is consistent with strong lensing of synchrotron emission near the event horizon of a spinning Kerr black hole, that ring radius and asymmetry are stable observables tied to mass and spin, that non-spinning models in the library fail to produce jets of sufficient power, and that jet power in viable models is extracted from black-hole spin via Blandford-Znajek-like processes. The spin vector is inferred to point away from Earth if aligned with the large-scale jet.

Significance. If the central claims hold, the work supplies direct observational support for the existence of black-hole shadows as predicted by general relativity and for spin-powered jets. The explicit predictions of stable ring radius and asymmetry furnish falsifiable tests for future EHT campaigns at 230 and 345 GHz. The systematic use of a GRMHD model library to compare visibilities is a methodological strength that, once fully documented, strengthens the result.

major comments (2)
  1. [Abstract] Abstract: the claim that 'models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets' is load-bearing for ruling out a = 0. No quantitative information is supplied on the number of a = 0 runs performed, the ranges sampled for accretion rate, magnetic flux, or disk thickness, the jet-power distribution, or the normalization used to compare with M87 observations. Without these statistics the completeness of the exclusion cannot be assessed.
  2. [Model comparison] Model-comparison section: the abstract states that observed visibilities were compared to the model library and found consistent, yet supplies no details on library size, parameter sampling density, the statistical fitting procedure, or error treatment. These omissions directly affect the verifiability of both the consistency claim for spinning models and the jet-power exclusion for non-spinning models.
minor comments (1)
  1. The abstract refers to 'future EHT campaigns at 230 and 345 GHz' without citing the relevant companion papers in the series; adding those references would improve traceability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful review and recommendation for minor revision. The two major comments correctly identify places where additional quantitative detail would strengthen verifiability. We address each point below and will revise the manuscript accordingly.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the claim that 'models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets' is load-bearing for ruling out a = 0. No quantitative information is supplied on the number of a = 0 runs performed, the ranges sampled for accretion rate, magnetic flux, or disk thickness, the jet-power distribution, or the normalization used to compare with M87 observations. Without these statistics the completeness of the exclusion cannot be assessed.

    Authors: We agree that the abstract claim would be more robust with explicit statistics. The full manuscript (Section 3 and Appendix) describes the GRMHD library construction and the jet-power normalization to the observed 1.3 mm flux, but does not tabulate the a=0 subset explicitly. In revision we will add a concise summary (new paragraph or table) stating the number of a=0 simulations performed, the sampled ranges in accretion rate, magnetic flux, and disk thickness, and the resulting jet-power distribution relative to the M87 requirement. This will allow readers to assess the completeness of the exclusion directly. revision: yes

  2. Referee: [Model comparison] Model-comparison section: the abstract states that observed visibilities were compared to the model library and found consistent, yet supplies no details on library size, parameter sampling density, the statistical fitting procedure, or error treatment. These omissions directly affect the verifiability of both the consistency claim for spinning models and the jet-power exclusion for non-spinning models.

    Authors: The referee is correct that the model-comparison methodology requires more explicit documentation for full reproducibility. While the manuscript outlines the overall approach (visibility comparison via ray-traced images), it does not provide the requested numerical details on library size, sampling grid, or error model. In the revised version we will expand the model-comparison section to report the total number of simulations and images, the parameter sampling strategy (spin, inclination, accretion rate, etc.), the statistical metric employed, and the treatment of thermal plus systematic uncertainties. These additions will directly address verifiability without altering the scientific conclusions. revision: yes

Circularity Check

0 steps flagged

No circularity: models generated from independent GRMHD equations and compared to separate EHT visibility data

full rationale

The paper constructs a library of GRMHD simulations and ray-traced images using standard general-relativistic magnetohydrodynamic equations and general-relativistic ray tracing, then compares those synthetic images to the independently measured EHT visibilities. The conclusions (consistency with spinning Kerr shadow, non-spinning models ruled out by jet power) follow from this external comparison rather than any self-definition, fitted parameter renamed as prediction, or reduction of the target result to the input data by construction. No load-bearing self-citation chains or ansatzes smuggled via prior work appear in the derivation chain described.

Axiom & Free-Parameter Ledger

3 free parameters · 3 axioms · 0 invented entities

Interpretation rests on standard GR plus GRMHD assumptions rather than new postulates; many simulation parameters (electron distribution, magnetic field geometry, accretion rate) are implicit in the model library but not enumerated in the abstract.

free parameters (3)
  • Black hole spin parameter a
    Controls ring asymmetry and jet power; constrained rather than freely fitted
  • Black hole mass M
    Sets ring radius scale; constrained by data
  • Inclination and plasma parameters
    Multiple GRMHD parameters (temperature, magnetization) implicit in library construction
axioms (3)
  • domain assumption General relativity accurately describes null geodesics and lensing near the event horizon
    Invoked to predict shadow size and ring asymmetry
  • domain assumption Synchrotron emission from thermal or non-thermal electrons in hot plasma orbiting near the horizon
    Source term for the radio emission in all models
  • domain assumption GRMHD equations plus chosen initial conditions produce representative accretion flows and jets
    Basis for the entire model library used for comparison

pith-pipeline@v0.9.0 · 5833 in / 1656 out tokens · 36209 ms · 2026-05-25T15:18:22.807194+00:00 · methodology

discussion (0)

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Forward citations

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Reference graph

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2 extracted references · 2 canonical work pages · cited by 10 Pith papers · 1 internal anchor

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