Estimating the Cosmological Constant from Shadows of Kerr–de Sitter Black Holes

The Event Horizon Telescope collaboration has revealed the first direct image of a black hole, as per the shadow of a Kerr black hole of general relativity. However, other Kerr-like rotating black holes of modified gravity theories cannot be ignored, and they are essential as they offer an arena in which these theories can be tested through astrophysical observation. This motivates us to investigate asymptotically de Sitter rotating black holes wherein interpreting the cosmological constant Λ as the vacuum energy leads to a deformation in the vicinity of a black hole—new Kerr–de Sitter solution, which has a richer geometric structure than the original one. We derive an analytical formula necessary for the shadow of the new Kerr–de Sitter black holes and then visualize the shadow of black holes for various parameters for an observer at given coordinates (r0,θ0) in the domain (r0,rc) and estimate the cosmological constant Λ from its shadow observables. The shadow observables of the new Kerr–de Sitter black holes significantly deviate from the corresponding observables of the Kerr–de Sitter black hole over an appreciable range of the parameter space. Interestingly, we find a finite parameter space for (Λ, a) where the observables of the two black holes are indistinguishable.

Investigation of the magnetized string distribution in the Marder universe with the cosmological term in f(R,T) theory

In this study, we first obtained the cosmological term naturally in the Einstein–Hilbert type effect for the [Formula: see text] theory, then we discussed the magnetized string matter in the Marder universe, later the matter Lagrangian is not equivalent to string dust and we calculated independently for the string dust and the electromagnetic field, and added the magnetized string together. Finally, we studied the physical and geometric structure of the universe, limiting our results to some astrophysical observation data.

Gravastar: An alternative to black hole

In this work, we review thoroughly the origin, development and present status of gravastar which has been thought to be an alternative to black hole along with its future feasibility in the sense of astrophysical observation. The Mazur–Mottola model of the gravastar is introduced first followed by a review of its generalizations within the context of general relativity including physical applications like primordial and cylindrical gravastars. The study of gravastar in higher- and lower-dimensional general relativity (GR) including the higher-dimensional theories with physical insight like the Randall–Sundrum model is presented. The gravastar models in a number of modified gravity models starting from [Formula: see text] to Rastall–Rainbow gravity have been reviewed.

Laboratory study of astrophysical collisionless shock at SG-II laser facility

Astrophysical collisionless shocks are amazing phenomena in space and astrophysical plasmas, where supersonic flows generate electromagnetic fields through instabilities and particles can be accelerated to high energy cosmic rays. Until now, understanding these micro-processes is still a challenge despite rich astrophysical observation data have been obtained. Laboratory astrophysics, a new route to study the astrophysics, allows us to investigate them at similar extreme physical conditions in laboratory. Here we will review the recent progress of the collisionless shock experiments performed at SG-II laser facility in China. The evolution of the electrostatic shocks and Weibel-type/filamentation instabilities are observed. Inspired by the configurations of the counter-streaming plasma flows, we also carry out a novel plasma collider to generate energetic neutrons relevant to the astrophysical nuclear reactions.

Travelling Scientist, Circulating Images and the Making of the Modern Scientific Journal

The early astrophysicist Norman Lockyer was both editor of the journal Nature from its creation in 1869 and for the following five decades, and an early practioner of the new astronomy. He frequently used the journal to expound his scientific theories, report on his work and send news home while on expeditions. I look into the particular visual culture of astrophysics developed by Lockyer in Nature, its evolution at a time of rapid development both of the techniques of astrophysical observation and visualization and of the techniques of image reproduction in print. A study of the use and reuse of visual materials in different settings also makes it possible to sketch the circulating economy of Lockyer’s images and the ways in which he put himself forward as a scientist, at a time when he was advocating the State support of research and scientists and helping create the modern scientific journal.

CONSTRAINTS FROM NEUTRINOLESS DOUBLE BETA DECAY

We examine the constraints from the recent HEIDELBERG–MOSCOW double beta decay experiment. It leads us to the almost degenerate or inverse hierarchy neutrino mass scenario. In this scenario, we obtain possible upper bounds for the Majorana CP violating phase in the lepton sector by incorporating the data from the neutrino oscillation, the single beta decay experiments, and from the astrophysical observation. We also predict the neutrino mass that may be measurable in the future beta decay experiments.