Robustness and the Event Horizon Telescope: the case of the first image of M87*

We examine the justification for taking the Event Horizon Telescope’s famous 2019 image to be a reliable representation of the region surrounding a black hole. We argue that it takes the form of a robustness argument, with the resulting image being robust across variation in a range of data-analysis pipelines. We clarify the sense of “robustness” operating here and show how it can account for the reliability of astrophysical inferences, even in cases—like the EHT—where these inferences are based on experiments that are (for all practical purposes) unique. This has consequences far beyond the 2019 image

2,6-Anhydro-1,3-di-O-benzyl-d-mannitol

In the title compound, C20H24O5, the six-membered pyran­ose ring adopts a chair conformation. The dihedral angle between the planes of the phenyl groups of the benzyl substituents is 63.1°. Two types of inter­molecular O—H⋯O hydrogen bonds lead to the formation of infinite chains along the b axis. Only weak C—H⋯O contacts exist between neighboring chains

Dimethyl hydrazine-1,2-dicarboxyl­ate–triphenyl­phosphine oxide (1/1)

In the crystal structure of the title compound, C4H8N2O4·C18H15OP, two triphenyl­phosphine oxide mol­ecules and two dimethyl hydrazine-1,2-dicarboxyl­ate mol­ecules are connected via N—H⋯O hydrogen bonds of moderate strength and are related via a twofold rotational axis. Weak Car—H⋯ O contacts strengthen the crystal structure

3-De­oxy-1,2-di-O-isopropyl­idene-5-O-tosyl-d-threo-pentofuran­ose

In the crystal structure of the title compound, C15H20O6S, the two independent mol­ecules crystalllize in a chiral setting with two different conformations, twisted 4 T 3 and envelope 4 E, for the furan­ose rings. Weak C—H⋯O contacts strengthen the crystal structure

On Penrose's Analogy between Curved Spacetime Regions and Optical Lenses

We present a detailed analysis of Penrose's gravito-optical analogy between the focusing effects of particular families of Ricci- and Weyl-curved spacetime regions on the one hand, and anastigmatic and astigmatic optical lenses on the other. We put the analogy in its historical context, investigate its underlying assumptions, its range of validity, its proof of concept, and its application in Penrose's study of the notion of energy flux in general relativity. Finally, we examine the analogy within the framework of Norton's material theory of induction

3′-O-Acetyl-2′-de­oxy­uridine

In the two independent but very similar mol­ecules of the title compound, C11H14N2O6, both nucleobase fragments are nearly planar (both within 0.01 Å) while the furan­ose rings exhibit 2 E-endo envelope conformations. In the crystal, the two 3′-O-acetyl-2′-de­oxy­uridine mol­ecules form a pseudosymmetric dimer of two bases connected via two nearly identical resonance-assisted N—H⋯O hydrogen bonds. The resulting pair is further connected with neighboring pairs via two similar O—H⋯O bonds involving the only hydroxyl group of the 2′-de­oxy­furan­ose fragment and the remaining carbonyl oxygen of the nucleobase. These inter­actions result in the formation of an infinite ‘double band’ along the b axis that can be considered as a self-assembled analogue of a polynucleotide mol­ecule with non-canonical Watson–Crick base pairs. The infinite chains of 3′-O-acetyl-2′-de­oxy­uridine pairs are additionally held together by C—H⋯O inter­actions involving C atoms of the uracyl base and O atoms of carbonyl groups. Only weak C—H⋯O contacts exist between neighboring chains

The Next Generation Event Horizon Telescope Collaboration: History, Philosophy, and Culture

This white paper outlines the plans of the History Philosophy Culture Working Group of the Next Generation Event Horizon Telescope Collaboration.Comment: 23 pages, 1 figur

Key Science Goals for the Next-Generation Event Horizon Telescope

The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply improve the angular resolution, dynamic range, and temporal coverage of the existing EHT observations. These improvements will uniquely enable a wealth of transformative new discoveries related to black hole science, extending from event-horizon-scale studies of strong gravity to studies of explosive transients to the cosmological growth and influence of supermassive black holes. Here, we present the key science goals for the ngEHT and their associated instrument requirements, both of which have been formulated through a multi-year international effort involving hundreds of scientists worldwide