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Inferring black hole physics through image and video reconstructions with the Event Horizon Telescope
No full text[EN] This thesis focuses on inferring black hole physics through the development and
application of advanced image and video reconstruction techniques using data
from the Event Horizon Telescope (EHT). The EHT, a global Very Long Baseline
Interferometry (VLBI) array, achieves unprecedented angular resolution by operating
at millimeter wavelengths (primarily 1.3 mm and 0.87 mm), enabling the horizonscale
study of supermassive black holes (SMBHs) like M87* in the galaxy M87 and
Sagittarius A* (Sgr A*) at the center of our Milky Way. The research presented herein
aims to extract quantitative astrophysical information from EHT observations, test
predictions of General Relativity (GR) in the strong-gravity regime, and provide
insights into the complex plasma dynamics governing accretion near these extreme
objects.
A core component of this research involved imaging the April 2018 EHT observations
of M87* utilizing the Bayesian interferometric modeling framework Comrade.
These analyses confirmed the persistence of the iconic asymmetric ring-like emission
structure, consistent with theoretical expectations of the shadow cast by a Kerr black
hole of approximately 6.5 × 109 solar masses (M⊙ ). The measured ring diameter
of ∼ 43.3+1.5
−3.1 μas was found to be remarkably consistent with the 2017 EHT
results, showing the stability of this gravitational feature. Moreover, a significant
counter-clockwise shift in the position angle of the ring’s brightness asymmetry by
approximately 30◦ was observed between the 2017 and 2018 epochs. This evolution
is attributed to the turbulent dynamics within the accretion flow, a phenomenon
seen in General Relativistic Magnetohydrodynamics (GRMHD) simulations. The
robust uncertainty quantification provided by the Bayesian approach was crucial in
assessing these features and investigating the challenges in constraining parameters
like the compact flux density of M87*.
Further investigation into the M87* images focused on quantitatively characterizing
and understanding the origin of the observed ring ellipticity. Leveraging the enhanced
(u, v)-coverage of the EHT 2018 array, which included the Greenland Telescope
(GLT) for improved North-South baseline sampling, a consistent ellipticity (τ =
0.08+0.03
−0.02) and major axis position angle (ξ = 50.1+6.2
−7.6 degrees East of North) were
measured across five independent imaging and modeling methods. To interpret
this measured ellipticity, an extensive comparison was performed against a large
library of GRMHD simulations, spanning a wide range of physical parameters
such as black hole spin, electron distribution functions (thermal and non-thermal),
magnetic field configurations (Magnetically Arrested Disk – MAD, and Standard and
Normal Evolution – SANE), and ion-to-electron temperature ratios. This analysis
revealed no statistically significant correlation between the black hole spin and the
observed image ellipticity. Instead, the ellipticity was found to correlate with the
fraction of non-ring emission, particularly in non-thermal models and those exhibiting
higher jet emission. These results compellingly suggest that the ellipticity measured
in the current EHT images of M87* is predominantly governed by astrophysical
effects within the turbulent accretion flow and jet base, rather than being a direct
manifestation of the gravitational lensing of an intrinsically elliptical photon ring
due to black hole spin. Isolating purely gravitational contributions to ellipticity will
necessitate future observations with enhanced capabilities or different observational
strategies.
The next frontier in black hole physics is to obtain the first event-horizon-scale
videos, particularly of rapidly variable sources like Sgr A*. Addressing the distinct
challenges posed by imaging such dynamic SMBHs, this thesis introduces ehteval,
a rigorous and systematic software framework developed for the validation and
evaluation of horizon-scale video reconstructions. The development of ehteval is
particularly relevant now as the EHT collaboration works towards producing these
first videos, making robust validation tools essential. This framework utilizes realistic
synthetic EHT datasets generated from a comprehensive library of ground truth
models, including static geometric models, dynamic geometric models with diverse
kinematic and polarimetric properties, and GRMHD simulations. A comprehensive
suite of evaluation metrics was developed and validated to quantitatively assess
reconstruction fidelity across multiple domains. These metrics probe the goodnessof-
fit to interferometric data products (e.g., closure phases, log-closure amplitudes,
complex fractional polarization), the morphological accuracy of total intensity and
linear polarization structures in both static (time-averaged) and dynamic (timevariable)
components, using normalized cross-correlations; and the ability to recover
specific dynamical features such as hotspot parameters (size, position, flux) and
rotational pattern speeds. The ehteval framework is foundational for interpreting
the first EHT video reconstructions of Sgr A*, and ensuring the robustness of scientific
conclusions drawn from these complex datasets.
Collectively, this thesis bridges the gap between raw interferometric observables
and interpretable physical quantities by combining rigorous image modeling with feature
extraction and simulation comparison. These tools offer a principled foundation
for interpreting horizon-scale observations of black holes and provide the groundwork
for exploiting future expansions of the EHT, including Space VLBI missions
capable of resolving fine structures such as photon subrings. By enabling reliable
characterization of dynamic and polarized features in black hole environments, this
work not only strengthens our ability to constrain accretion physics and spacetime
geometry but also contributes to the development of next-generation techniques in
computational astrophysics.[ES] Esta tesis se centra en inferir la física de los agujeros negros mediante el desarrollo y la
aplicación de técnicas avanzadas de reconstrucción de imágenes y vídeos utilizando
datos del Telescopio del Horizonte de Sucesos (EHT). El EHT, una red global de
Interferometría de Muy Larga Base (VLBI), alcanza una resolución angular sin
precedentes al operar en longitudes de onda milimétricas (principalmente 1.3 mm
y 0.87 mm), lo que permite el estudio a escala del horizonte de sucesos de agujeros
negros supermasivos (SMBH) como M87* en la galaxia M87 y Sagitario A* (Sgr A*) en
el centro de nuestra Vía Láctea. La investigación aquí presentada tiene como objetivo
extraer información astrofísica cuantitativa de las observaciones del EHT, probar
las predicciones de la Relatividad General (RG) en el régimen de gravedad fuerte y
proporcionar información sobre la compleja dinámica del plasma que gobierna la
acreción cerca de estos objetos extremos.
Un componente central de esta investigación implicó la obtención de imágenes de
las observaciones de M87* del EHT de abril de 2018 utilizando el marco bayesiano
de modelado interferométrico Comrade. Estos análisis confirmaron la persistencia
de la icónica estructura de emisión en forma de anillo asimétrico, consistente con
las expectativas teóricas de la sombra proyectada por un agujero negro de Kerr de
aproximadamente 6.5×109 masas solares (M⊙). Se encontró que el diámetro medido
del anillo de ∼ 43.3+1.5
−3.1 μas era notablemente consistente con los resultados del EHT
de 2017, lo que subraya la estabilidad de esta característica gravitacional. Además,
se observó un desplazamiento significativo en sentido antihorario en el ángulo de
posición de la asimetría de brillo del anillo de aproximadamente 30◦ entre las épocas
de 2017 y 2018. Esta evolución se atribuye a la dinámica turbulenta dentro del flujo
de acreción, un fenómeno observado en las simulaciones Magnetohidrodinámica
Relativista General (GRMHD).La cuantificación robusta de incertidumbre del enfoque
bayesiano fue clave para evaluar estas características y explorar los retos al restringir
parámetros como la densidad de flujo compacto de M87*.
Una investigación adicional de las imágenes de M87* se centró en caracterizar
cuantitativamente y comprender el origen de la elipticidad observada del anillo.
Aprovechando la mejorada cobertura (u, v) de la red EHT 2018, que incluyó el
Telescopio de Groenlandia (GLT) para un mejor muestreo de las líneas de base
Norte-Sur, se midió una elipticidad consistente (τ = 0.08+0.03
−0.02) y un ángulo de
posición del eje mayor (ξ = 50.1+6.2
−7.6 grados al Este del Norte) a través de cinco
métodos independientes de obtención de imágenes y modelado. Para interpretar esta
elipticidad medida, se realizó una comparación exhaustiva con una gran biblioteca
de simulaciones GRMHD, que abarca una amplia gama de parámetros físicos como
el espín del agujero negro, las funciones de distribución de electrones (térmicas y no
térmicas), las configuraciones del campo magnético (Disco Magnéticamente Detenido
– MAD, y Evolución Estándar y Normal – SANE), y las relaciones de temperatura
ion-electrón. Este análisis no reveló ninguna correlación estadísticamente significativa
entre el espín del agujero negro y la elipticidad observada de la imagen. En cambio,
se encontró que la elipticidad se correlaciona con la fracción de emisión no anular,
particularmente en modelos no térmicos y aquellos que exhiben una mayor emisión de
jet. Estos resultados sugieren de manera convincente que la elipticidad medida en las
imágenes actuales del EHT de M87* está predominantemente gobernada por efectos
astrofísicos dentro del flujo de acreción turbulento y la base del jet, en lugar de ser una
manifestación directa de la lente gravitacional de un anillo de fotones intrínsecamente
elíptico debido al espín del agujero negro. Aislar las contribuciones puramente
gravitacionales a la elipticidad requerirá futuras observaciones con capacidades
mejoradas o diferentes estrategias de observación.
La próxima frontera en la física de los agujeros negros es obtener los primeros
vídeos a escala del horizonte de sucesos, particularmente de fuentes rápidamente
variables como Sgr A*. Abordando los distintos desafíos que plantea la obtención
de imágenes de tales SMBH dinámicos, esta tesis presenta ehteval, un marco de
software riguroso y sistemático desarrollado para la validación y evaluación de
reconstrucciones de vídeo a escala del horizonte. El desarrollo de ehteval es particularmente
relevante ahora que la colaboración EHT trabaja para producir estos
primeros vídeos, lo que hace esenciales herramientas de validación robustas. Este
marco utiliza conjuntos de datos sintéticos realistas del EHT generados a partir de
una biblioteca completa de modelos de "ground truth", incluidos modelos geométricos
estáticos, modelos geométricos dinámicos con diversas propiedades cinemáticas y
polarimétricas, y simulaciones GRMHD. Se desarrolló y validó un conjunto completo
de métricas de evaluación para evaluar cuantitativamente la fidelidad de la reconstrucción
en múltiples dominios. Estas métricas sondean la bondad del ajuste a los
productos de datos interferométricos (p. ej., fases de cierre, log-amplitudes de cierre,
polarización fraccional compleja), la precisión morfológica de las estructuras de intensidad
total y polarización lineal en componentes tanto estáticos (promediados en el
tiempo) como dinámicos (variables en el tiempo), utilizando correlaciones cruzadas
normalizadas; y la capacidad de recuperar características dinámicas específicas como
los parámetros de los puntos calientes (tamaño, posición, flujo) y las velocidades del
patrón de rotación. El marco ehteval es fundamental para interpretar las primeras reconstrucciones
de vídeo del EHT de Sgr A* y garantizar la solidez de las conclusiones
científicas extraídas de estos complejos conjuntos de datos.
Colectivamente, esta tesis cierra la brecha entre las observables interferométricas
crudas y las cantidades físicas interpretables al combinar un modelado riguroso de
imágenes con la extracción de características y la comparación de simulaciones. Estas
herramientas ofrecen una base de principios para interpretar las observaciones a
escala del horizonte de los agujeros negros y sientan las bases para explotar futuras
expansiones del EHT, incluidas las misiones espaciales VLBI capaces de resolver
estructuras finas como los subanillos de fotones. Al permitir una caracterización
fiable de las características dinámicas y polarizadas en los entornos de los agujeros
negros, este trabajo no solo fortalece nuestra capacidad para restringir la física de la
acreción y la geometría del espaciotiempo, sino que también contribuye al desarrollo
de técnicas de próxima generación en astrofísica computacional.I am grateful for the support of the INPhINIT doctoral fellowship from "la Caixa"
Foundation (ID 100010434, fellowship code LCF/BQ/DI22/11940030), which enabled
this doctoral work at the Instituto de Astrofísica de Andalucía (IAA-CSIC).
I am also thankful for the support from the Spanish Ministerio de Ciencia, Innovación
y Universidades through grant PID2022-140888NB-C21 and the Severo Ochoa grant
CEX2021-001131-S funded by MICIU/AEI/10.13039/501100011033.With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).Peer reviewe
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
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koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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