The Event Horizon Telescope image of the supermassive black hole in the galaxy M87 is dominated by a bright, unresolved ring. General relativity predicts that embedded within this image lies a thin ..."photon ring," which is composed of an infinite sequence of self-similar subrings that are indexed by the number of photon orbits around the black hole. The subrings approach the edge of the black hole "shadow," becoming exponentially narrower but weaker with increasing orbit number, with seemingly negligible contributions from high-order subrings. Here, we show that these subrings produce strong and universal signatures on long interferometric baselines. These signatures offer the possibility of precise measurements of black hole mass and spin, as well as tests of general relativity, using only a sparse interferometric array.
Measuring Photon Rings with the ngEHT Tiede, Paul; Johnson, Michael D.; Pesce, Dominic W. ...
Galaxies,
12/2022, Letnik:
10, Številka:
6
Journal Article
Recenzirano
Odprti dostop
General relativity predicts that images of optically thin accretion flows around black holes should generically have a “photon ring”, composed of a series of increasingly sharp subrings that ...correspond to increasingly strongly lensed emission near the black hole. Because the effects of lensing are determined by the spacetime curvature, the photon ring provides a pathway to precise measurements of the black hole properties and tests of the Kerr metric. We explore the prospects for detecting and measuring the photon ring using very long baseline interferometry (VLBI) with the Event Horizon Telescope (EHT) and the next-generation EHT (ngEHT). We present a series of tests using idealized self-fits to simple geometrical models and show that the EHT observations in 2017 and 2022 lack the angular resolution and sensitivity to detect the photon ring, while the improved coverage and angular resolution of ngEHT at 230 GHz and 345 GHz is sufficient for these models. We then analyze detection prospects using more realistic images from general relativistic magnetohydrodynamic simulations by applying “hybrid imaging”, which simultaneously models two components: a flexible raster image (to capture the direct emission) and a ring component. Using the Bayesian VLBI modeling package Comrade.jl, we show that the results of hybrid imaging must be interpreted with extreme caution for both photon ring detection and measurement—hybrid imaging readily produces false positives for a photon ring, and its ring measurements do not directly correspond to the properties of the photon ring.
What Reason Promises Doniger, Wendy; Galison, Peter; Neiman, Susan
2016, 2016-06-20
eBook
This collection demonstrates the range of approaches that some of the leading scholars of our day take to basic questions at the intersection of the natural and human worlds. The essays focus on ...three interlocking categories: Reason stakes a bigger territory than the enclosed yard of universal rules. Nature expands over a far larger region than an eternal category of the natural. And history refuses to be confined to claims of an unencumbered truth of how things happened.
In surveying the field of history and philosophy of science (HPS), it may be more useful just now to pose some key questions than it would be to lay out the sundry competing attempts to unify H and ...P. The ten problems this essay presents are grounded in a range of work of enormous interest—historical and philosophical work that has made use of productive categories of analysis: context, historicism, purity, and microhistory, to name but a few. What kind of account are we after—historically and philosophically—when we attempt to address science not as a vacuous generality but in its specific, local formation?
Galison infers that secrecy, if pressed too hard and too deeply measured in the staggering units of Libraries of Congress, will become a threat to democracy. He states that it is not a problem to be ...resolved by an automated Original Classifier or declassifier, rather, it is political at every scale, from attempts to excise a single critical idea to the vain efforts to remove whole domains of knowledge.
Secrecy in Three Acts Galison, Peter
Social research,
09/2010, Letnik:
77, Številka:
3
Journal Article
Recenzirano
In June 1979, Congress passed the Espionage Act, the first act of the three secrecy-defining statutes that have shaped so much of the last hundred years of modern American secrecy doctrine. Together ...with two other statutes that followed in later decades-the Atomic Energy Acts of 1946 and 1954, and the Patriot Act of 2001-these three Acts picked out inflection points in the great ratcheting process that has expanded secrecy from the protection of troop positions and recruitment stations through an entire field of the physical sciences to almost the whole of government and civil society. Along with a surround of orders, directives, laws, and policies, these three Acts ground the modern world of national security secrecy. Necessarily schematic, my aim here is to follow the long term history of secrets over the last hundred years, using the debates and cases that that encircled them to understand better the governing principles of what information had to be hidden. What dangers did each period identify among things that should be secret? What were the properties and assumed power of these secrets? What kind of thing could, in the end, properly be declared secret? In short, I am interested in using the Acts to fix what it is that secrets were: An historically changing ontology of secrets from World War I through the Long War (World War II through the Cold War), and finally into the Terror Wars, our unbounded conflict. Adapted from the source document.
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