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"Falconry"
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Testing the nature of dark compact objects: a status report
Very compact objects probe extreme gravitational fields and may be the key to understand outstanding puzzles in fundamental physics. These include the nature of dark matter, the fate of spacetime singularities, or the loss of unitarity in Hawking evaporation. The standard astrophysical description of collapsing objects tells us that massive, dark and compact objects are black holes. Any observation suggesting otherwise would be an indication of beyond-the-standard-model physics. Null results strengthen and quantify the Kerr black hole paradigm. The advent of gravitational-wave astronomy and precise measurements with very long baseline interferometry allow one to finally probe into such foundational issues. We overview the physics of exotic dark compact objects and their observational status, including the observational evidence for black holes with current and future experiments.
Journal Article
The hawk of the castle : a story of medieval falconry
\"Join a young girl and her father, the falconer at a medieval castle, as they experience the joys of taking a goshawk out for a training flight. The girl leads readers through all the preparations and equipment needed for the flight -- from falconer's glove to the hawk's hood and bells -- culminating in a dramatic demonstration of the hawk's hunting skills.\" -- From dust jacket.
Book
Stability and Hawking-Page-like phase transition of phantom AdS black holes
In this work, we investigate the thermodynamic stability and phase structure of AdS black holes with either a Maxwell field (where we revisit past studies) or a phantom field. We conduct a comprehensive analysis of the free energy and temperature of these systems in both the canonical and grand canonical ensembles. Our findings reveal the occurrence of a phase transition in the grand canonical ensemble, resembling the Hawking-Page-like phase transition observed between the thermal radiation of AdS spacetime and thermodynamically stable large black holes. We present graphical representations of these phase transitions on free energy-temperature diagrams for the black holes. Completing our study, we obtain the transition temperature, minimum temperature and their dual relations.
Journal Article
Digital predation: scale, drivers and conservation implications of illegal online trade in raptors in Pakistan
Illegal wildlife trade is a major driver of biodiversity loss, and online platforms are increasingly used to advertise protected wildlife. In Pakistan, raptor trade is increasingly mediated by online marketplaces, reflecting a wider global transition. As a case study, we assessed the online trade in raptors in Pakistan from January 2021 to December 2023 by monitoring groups on the social media platforms Facebook, Instagram, YouTube, TikTok and WhatsApp, and local e-commerce websites, using keyword-based searches, with cross-checking to reduce duplication and misidentification. We recorded 310 raptors advertised for sale from 92 seller accounts, representing 24 species across four families. Falconidae comprised 61% of individuals and Accipitridae 37%, with peregrine falcon Falco peregrinus and saker falcon Falco cherrug the most frequently advertised species. A substantial proportion of listings involved species protected under provincial wildlife legislation, as well as species listed under CITES and categorized as threatened on the IUCN Red List. Using a generalized linear model, we found that asking prices were higher for threatened and visitor species. Seller activity was concentrated in Punjab and Khyber Pakhtunkhwa, and Facebook accounted for the largest share of records, indicating that improved monitoring and enforcement on this platform is a priority. Our findings provide baseline evidence to support demand-reduction outreach, community reporting and capacity building within wildlife agencies, alongside improved online detection tools and updated assessments of raptor population status in Pakistan, particularly for migratory species using the Central Asian Flyway.
Journal Article
Reentrant Hawking–Page phase transition of charged Gauss–Bonnet-AdS black holes in the grand canonical ensemble
In this paper, we study the reentrant Hawking–Page transition in the grand canonical ensemble of Gauss–Bonnet AdS spacetime. We find that the four-dimensional Gauss–Bonnet hyperbolic AdS black hole always has a reentrant Hawking–Page transition in the range of electric potential
0
<
Φ
<
Φ
tr
, accompanied by the appearance of the triple point. However, once the potential exceeds a certain upper limit
Φ
tr
, i.e.
Φ
>
Φ
tr
, the Hawking–Page transition disappears. In the spacetime of five and higher dimensional Gauss–Bonnet hyperbolic AdS black hole, the reentrant Hawking–Page transition is solely observed to occur when the electric potential
Φ
lies between two specific thresholds (
Φ
c
<
Φ
<
Φ
tr
). In scenarios where the electric potential is below
Φ
c
(
Φ
<
Φ
c
), only the standard Hawking–Page transition as in the the Einstein gravity is observed. Similar to the four-dimensional case, the Hawking–Page transition is negated when the electric potential exceeds
Φ
tr
(
Φ
>
Φ
tr
). We give the coexistence line, the triple point and critical point of the Hawking–Page transition in the phase diagram of the Gauss–Bonnet hyperbolic AdS black hole. The observed reentrant Hawking–Page transitions and triple points in the context of Gauss–Bonnet hyperbolic AdS black holes may correspond to the phase transitions and triple points in QCD phase diagrams, following the spirit of the AdS/CFT correspondence. To be a complete research, the Hawking–Page transition of d-dimensional charged spherical Gauss–Bonnet-AdS black hole in the grand canonical ensemble is also study in the Appendix, for which there exists a standard Hawking–Page transition with the transition temperature depending on the Gauss–Bonnet constant
α
.
Journal Article
Hawking temperature as the total Gauss–Bonnet invariant of the region outside a black hole
We provide two novel ways to compute the surface gravity (
κ
) and the Hawking temperature
(
T
H
)
of a stationary black hole: in the first method
T
H
is given as the three-volume integral of the Gauss–Bonnet invariant (or the Kretschmann scalar for Ricci-flat metrics) in the total region outside the event horizon; in the second method it is given as the surface integral of the Riemann tensor contracted with the covariant derivative of a Killing vector on the event horizon. To arrive at these new formulas for the black hole temperature (and the related surface gravity), we first construct a new differential geometric identity using the Bianchi identity and an antisymmetric rank-2 tensor, valid for spacetimes with at least one Killing vector field. The Gauss–Bonnet tensor and the Gauss–Bonnet scalar play a particular role in this geometric identity. We calculate the surface gravity and the Hawking temperature of the Kerr and the extremal Reissner–Nordström holes as examples.
Journal Article