36th Annual Report (2023-24)

179 AreasofResearch The ICARD at the Department of Physics, Gauhati University, was active from October 2022. It hosts research activities in gravitation & cosmology, as well as observational astronomy. The ICARD has two permanent faculty members in Astronomy & Astrophysics – Sanjeev Kalita andBiman JMedhi. Sanjeev Kalita's research studies include testability of modified gravity theories near the Galactic Centre black hole through upcoming Extremely Large Telescopes, expansion history of the universe outside Lambda CDM cosmology, formation of massive black holes in the high redshift universe and early universe physics. He also carries out historical research studies on astronomy. Biman J Medhi is involved in the observational studies of active galactic nuclei through X-ray astronomy, star f o rma t i on and s t a r c l us t e r s and polarimetric studies of galactic dust clouds and comets. He is also interested in studying exoplanets and their connection with host star properties . A possible combination of early universe physics and late-time cosmologies in gravitation and cosmology has been investigated with the observed BAO scales. It is found that cosmological models with curvature and departure from general relativity are promising with BAO alone. Age has been found to be elevated in some of these alternatives to Lambda CDM and is found compatible with available reports of very old star clusters. The possibility of the formation ofmassive black hole seeds in the pre-quasar era has been investigated through the accretion of Self Interacting Dark Matter. f(R) gravity scalarons and Primordial Black Hole mass have been constrained through observed bounds on primordial heliumabundance. A Kerr metric was constructed in these theories with the NJA algorithm to study the Research testability of f(R) gravity theories near the Galactic Centre black hole. Astronomical consequences such as effects on black holes shadows, Lense-Thirring precession of compact stellar orbits and Schwarzschild precession were studied. It has been reported that scalaron degrees of freedom with masses 10 – 17 - 10 – 16 eV are consistent with general relativity. In observational astronomy, observations from XMM Newton, Swift and NuSTAR were used to study X-ray/UV correlation in Seyfert galaxies. Through Gaia DR 3 astrometric data of stars in open clusters, a statistical and multiwavelength study was carried ou t for the open cluster IC 1590. With the help of AIMPOL at ARIES, Nainital, the magnetic field and dust grain properties of two galactic dust clouds L 1495 and L 1 4 9 8 w e r e s t u d i e d t h r o u g h photopolarimetry. An astronomy workshop for college and university teachers titled 'Pedagogic Workshop/SchoolOrganised Coordinator: Dr. Sanjeev Kalita ICARD - Department of Physics, Gauhati University, Gauhati (Activities from 01 April 2023 to 31 March 2024) 6. Considering the cosmological constant as the positive pressure of the system and volume as its conjugate variable, we analyse the thermodynamics of various black holes in the extended phase space. Owing to the deviation parameter from the modified theories, we analyse the Hawking temperature, entropy and specific heat. We also investigate the relationship between the photon sphere radius and the phase transition AdS black holes. We can regard both the changes of photon sphere radius and impact parameter before and after phase transition as the order parameter; their critical exponents near the critical point are equal to the same value 1/2, just like ordinary thermal systems. These indicate that a universal relation of gravity may exist near the crucial point in a black hole thermodynamic system. Workshops/schoolsorganised 1. Indo-South Africa Workshop on Astrophysics September 27-29, 2023. 2. National ScienceDay February 28, 2024 Poster Display with Explanation by PhD scholars Talks by Eminent Speakers 3. Special Lecture Series on Cosmology and Astrophysics. The inaugural by Prof M Sami, Director, CCSP), SGT University ¬ ¬ -February 20, 2024, at 3:30pm PublicationsusingICARDfacilities The publications are included under 'Publications by Visiting Associates'. Outreach programmes, including public lectures/skywatcharrangedbyICARD 1. National ScienceDay February 28, 2024 2. Poster Display with Explanation by PhD scholars - February 28, 2024 Honours/distinctions/awards,etc. Prof Anjan Sen is elected the General Secretary of IAGRG.