Semi-Analytic Radiatively Inefficient Accretion Flows in General Gravity

The Event Horizon Telescope is capable of observing black holes on event-horizon scales and we can use it to explore deviations from General Relativity. We replicate the results of a previous study using a Newtonian prescription of gravity to set a suitable limit to justify viscosity and radiation choices. We also create a framework to explore semi-analytic models of Radiatively Inefficient Accretion Flows with a covariant prescription of gravity. We study a Kerr-like metric not described by General Relativity, and find only small deviations from Kerr solutions. We also find that the dynamics of the flow are sensitive to small General Relativistic effects

Using Black Hole Environments as Laboratories for Testing Accretion and Gravity

With the advent of the Event Horizon Telescope (EHT), we have the ability to observe the lensed emission from hot plasmas near event horizons. It contains entangled information about the turbulent magnetohydrodynamic accretion processes and the black hole spacetime. We present studies of both coherent and stochastic variable features measurable from EHT data, and by applying them to libraries of simulations, we describe how they inform on the underlying accretion flow. For a rapidly varying source like Sgr A*, we find that variability is greatest on the largest spatial scales and the longest timescale, and find a universal power-law variability prescription in the visibility domain. For a slowly varying source like M87*, we measure a correlation timescale and a rotation rate, which is inconsistent with the velocity of the fluid causing the emission. The strong predictions from the simulations of the variability measures we create are consistent with current EHT data. We also create a static analytical midplane accretion flow model and use variable simulations to motivate a prescription to incorporate turbulent effects. Our model matches SANE models well and struggles with the more variable MAD models. It can incorporate non-Kerr metrics, can connect the black hole scales to their large-scale environment, and can be incorporated in existing parameter estimation frameworks to fit EHT data

Photon Rings and Shadow Size for General Integrable Spacetimes

There are now multiple direct probes of the region near black hole horizons, including direct imaging with the Event Horizon Telescope (EHT). As a result, it is now of considerable interest to identify what aspects of the underlying spacetime are constrained by these observations. For this purpose, we present a new formulation of an existing broad class of integrable, axisymmetric, stationary spinning black hole spacetimes, specified by four free radial functions, that makes manifest which functions are responsible for setting the location and morphology of the event horizon and ergosphere. We explore the size of the black hole shadow and high-order photon rings for polar observers, approximately appropriate for the EHT observations of M87*, finding analogous expressions to those for general spherical spacetimes. Of particular interest, we find that these are independent of the properties of the ergosphere, but does directly probe on the free function that defines the event horizon. Based on these, we extend the nonperturbative, nonparametric characterization of the gravitational implications of various near-horizon measurements to spinning spacetimes. Finally, we demonstrate this characterization for a handful of explicit alternative spacetimes

Shadow Implications: What does measuring the photon ring imply for gravity?

With the imaging and characterization of the horizon-scale images of M87* and Sgr A* by the Event Horizon Telescope (EHT), it has become possible to resolve the near-horizon region of astrophysical black holes. As a result, there has been considerable interest in the implications of the measurement of the shadow size, i.e., the asymptotic photon ring. We explore the general implications of such a measurement, identifying what is and, more importantly, is not constrained by such measurements, with applications to EHT and future instruments. We consider a general spherically symmetric metric, which effectively applies for a polar observer (appropriate for M87*) in the slow rotation limit. We propose a nonperturbative, nonparametric spacetime-domain characterization of shadow size and related measurements that makes explicit the nature and power (or lack thereof) of shadow-size-based constraints, and facilitates comparisons among observations and targets.Comment: Submitted to ApJ, 16 pages, 5 figure

Priapism in an otherwise healthy man with SARS-COV-2: case report and literature review

COVID-19 disease causes acute respiratory infection – pneumonia. It is associated with an increased risk of complications such as hypercoagulopathy, which leads to thromboses. We present a case of a young man presenting with typical SARS-CoV-2 symptoms (fever, cough, fatigue, and dyspnea), who experienced ischemic priapism, most probably due to thrombosis of penile vessels caused by the novel coronavirus infection. After prompt treatment of the priapism with punctures and irrigation, lasting penile detumescence was achieved. However, despite younger age, lack of serious comorbidities and administration of anticoagulants, priapism was followed by a fatal pulmonary embolism some days later

Rotation in Event Horizon Telescope Movies

The Event Horizon Telescope (EHT) has produced images of M87* and Sgr A*, and will soon produce time sequences of images, or movies. In anticipation of this, we describe a technique to measure a rotation rate, or pattern speed $\Omega_p$, from movies using an autocorrelation technique. We validate the technique on Gaussian random field models with a known rotation rate and apply it to a library of synthetic images of Sgr A* based on general relativistic magnetohydrodynamics (GRMHD) simulations. We predict that EHT movies will have $\Omega_p \approx 1$ degree per $\mathrm{GMc^{-3}}$, which is of order $15\%$ of the Keplerian orbital frequency in the emitting region. We can plausibly attribute the slow rotation seen in our models to the pattern speed of inward-propagating spiral shocks. We also find that $\Omega_p$ depends strongly on inclination. Application of this technique will enable us to compare future EHT movies with the clockwise rotation of Sgr A* seen in near-infrared flares by GRAVITY. Pattern speed analysis of future EHT observations of M87* and Sgr A* may also provide novel constraints on black hole inclination and spin, as well as an independent measurement of black hole mass

Market trends in meat and meat product prices: Analyzing the cost price of energy value in meat products

This study provides an overview of food prices in the Republic of Serbia from 2016 to 2023 amidst the challenges faced by the meat processing industry. Household spending trends reveal a notable shift, marking an increase since 2016. The study explores meat products' affordability and nutrient density, challenging conventional assumptions. Mortadella emerges as the most nutrient-dense despite its lower calorie content due to high protein content, while pâté commands a higher market price despite its lower nutrient quality

Drivers, opportunities, and challenges of the European risk-based meat safety assurance system

The traditional meat safety system has significantly contributed to public health protection throughout the last century. However, it has been recognised that this system suffers many flaws ? the main being its limited ability to control the currently most important meat-borne hazards. The European Food Safety Authority evaluated meat inspection in the public health context, prioritised meat-borne hazards and proposed a generic framework for a new, risk-based meat safety assurance system. The proposed system aims to combine a range of preventive and control measures, applied at farms and abattoirs and integrated longitudinally, where official meat inspection is incorporated with producers? food safety management systems into a coherent whole. The modernisation process has recently started as a direct result of changes to relevant legislation in the European Union. Many challenges have been experienced while many opportunities are foreseen. More focus on targeted and risk-based inspection along the supply chain as well as use of new technologies may be a cost-effective and feasible way forward. Practical implementation of the system is expected to be a slow and careful process followed by thorough development, fine-tuning, and testing of practical feasibility and general impacts. Further progress that will lead to the full implementation is dependent on intensive research to fill knowledge gaps, enhance education and training and foster close collaboration of all the new system?s stakeholders

The Photon Ring in M87*

We report measurements of the gravitationally lensed secondary image—the first in an infinite series of so-called “photon rings”—around the supermassive black hole M87* via simultaneous modeling and imaging of the 2017 Event Horizon Telescope (EHT) observations. The inferred ring size remains constant across the seven days of the 2017 EHT observing campaign and is consistent with theoretical expectations, providing clear evidence that such measurements probe spacetime and a striking confirmation of the models underlying the first set of EHT results. The residual diffuse emission evolves on timescales comparable to one week. We are able to detect with high significance a southwestern extension consistent with that expected from the base of a jet that is rapidly rotating in the clockwise direction. This result adds further support to the identification of the jet in M87* with a black hole spin-driven outflow, launched via the Blandford-Znajek process. We present three revised estimates for the mass of M87* based on identifying the modeled thin ring component with the bright ringlike features seen in simulated images, one of which is only weakly sensitive to the astrophysics of the emission region. All three estimates agree with each other and previously reported values. Our strongest mass constraint combines information from both the ring and the diffuse emission region, which together imply a mass-to-distance ratio of 4.20 − 0.06 + 0.12 μ as and a corresponding black hole mass of (7.13 \ub1 0.39) 7 109 M ⊙, where the error on the latter is now dominated by the systematic uncertainty arising from the uncertain distance to M87*