A5027077715- Galaxies: Formation, Evolution, Phenomena
- Astrophysical Phenomena and Observations
- Astrophysics and Star Formation Studies
- Stellar, planetary, and galactic studies
- Cosmology and Gravitation Theories
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Pulsars and Gravitational Waves Research
- Astrophysics and Cosmic Phenomena
- Solar and Space Plasma Dynamics
- Radio Astronomy Observations and Technology
- Advanced Cellulose Research Studies
- Astro and Planetary Science
- Lignin and Wood Chemistry
- Relativity and Gravitational Theory
- Advanced Sensor and Energy Harvesting Materials
- Natural Fiber Reinforced Composites
- Dark Matter and Cosmic Phenomena
- Conducting polymers and applications
- Black Holes and Theoretical Physics
- Additive Manufacturing and 3D Printing Technologies
- Advanced X-ray and CT Imaging
- Supercapacitor Materials and Fabrication
- Electrospun Nanofibers in Biomedical Applications
- Health and Lifestyle Studies
United Arab Emirates University
2017-2025
Federal Urdu University
2024
Inha University
2021-2024
Government College University, Lahore
2022-2023
Government College Women University Sialkot
2022-2023
Oman Dental College
2020
Oman Medical College
2020
Sorbonne Université
2014-2018
Centre National de la Recherche Scientifique
2015-2018
Institut d'Astrophysique de Paris
2014-2018
Supermassive black holes with up to a 109 M⊙ dwell in the centres of present-day galaxies, and their presence has been confirmed at z ≥ 6. Their formation such early epochs is still an enigma. Different pathways have suggested assemble supermassive first billion years after big bang. Direct collapse emerged as highly plausible scenario form it provides seed masses 105–106 M⊙. Gravitational atomic cooling haloes virial temperatures Tvir 104 K may lead massive intense background ultraviolet...
Black holes of a billion solar masses are observed in the infant Universe few hundred million years after big bang. The direct collapse protogalactic gas clouds primordial haloes with Tvir ≥ 104 K provides most promising way to assemble massive black holes. In this study, we aim determine characteristic mass scale seed and time evolution accretion rates resulting from model. We explore formation supermassive via cosmological large eddy simulations (LES) by employing sink particles following...
Supermassive stars and quasi-stars (massive with a central black hole) are both considered as potential progenitors for the formation of supermassive holes. They expected to form from rapidly accreting protostars in massive primordial halos. We explore how long remain on Hayashi track, implying large protostellar radii weak accretion luminosity feedback. assess role energy production nuclear core, determine what regulates evolution such into or stars. follow contraction characteristic mass...
Supermassive black holes (BHs) of millions solar masses and above reside in the center most local galaxies, but they also power active galactic nuclei quasars, detected up to z=7. This observational evidence puts strong constraints on BH growth mass first seeds. The scenario "direct collapse" is very appealing as it leads formation large seeds range 10^4-10^6 Msun, which eases explaining how quasars at z=6-7 are powered by BHs with >10^9 Msun. Direct collapse, however, appears be rare,...
Observations of high-redshift quasars at z > 6 indicate that they harbour supermassive black holes (SMBHs) a billion solar masses. The direct collapse scenario has emerged as the most plausible way to assemble SMBHs. nurseries for are massive primordial haloes illuminated with an intense UV flux emitted by Population II (Pop II) stars. In this study, we compute critical value such (|$J_{21}^{\rm crit}$|) realistic spectra Pop stars through three-dimensional cosmological simulations. We...
The detection of quasars at $z>6$ unveils the presence supermassive black holes (BHs) a few billion solar masses. rapid formation process these extreme objects remains fascinating and open issue. Such discovery implies that seed must have formed early on, grown via either accretion or BH/galaxy mergers. In this theoretical review, we discuss in detail various BH mechanisms physical processes play during their assembly. We three most popular scenarios, involving (i) core-collapse massive...
Population III (Pop III) stars ended the cosmic Dark Ages and began early cosmological reionization chemical enrichment. However, in spite of their importance to evolution Universe, properties remain uncertain because limitations previous numerical simulations lack any observational constraints. Here we investigate Pop star formation five primordial halos with 3D radiation-hydrodynamical simulations. We find that multiple form each minihalo numbers increase over time, up 23 forming one...
The ability of metal free gas to cool by molecular hydrogen in primordial halos is strongly associated with the strength ultraviolet (UV) flux produced stellar populations first galaxies. Depending on spectrum, these UV photons can either dissociate $\rm H_{2}$ molecules directly or indirectly photo-detachment H^{-}$ as latter provides main pathway for formation early universe. In this study, we aim determine critical above which remains suppressed a sample five distinct at $z>10$ employing...
While present standard model of cosmology yields no clear prediction for the initial magnetic field strength, efficient dynamo action may compensate initially weak seed fields via rapid amplification. In particular, small-scale is expected to exponentially amplify any in presence turbulence. We explore whether this scenario viable using cosmological magneto-hydrodynamics simulations modeling formation first galaxies, which are form so-called atomic cooling halos with virial temperatures $\rm...
In recent years, the discovery of massive quasars at z~7 has provided a striking challenge to our understanding origin and growth supermassive black holes in early Universe. Mounting observational theoretical evidence indicates viability seeds, formed by collapse stars, as progenitor model for such early, accreting holes. Although considerable progress been made understanding, many questions remain regarding how (and often) objects may form, they live die, next generation observatories yield...
The semi-analytical model A-SLOTH (Ancient Stars and Local Observables by Tracing Halos) is the first public code that connects formation of stars galaxies to observables. After several successful projects with this model, we publish source describe version in paper. based on dark matter merger trees can either be generated Extended Press-Schechter theory or imported from simulations. On top these trees, applies analytical recipes for baryonic physics both metal-free metal-poor transition...
Nanocellulose (NC)-based piezoelectric films prepared via solution casting show low mechanical, dielectric, and performance due to the randomly oriented cellulose nanofibers dispersion of domains. Moreover, a high electric field for domain alignment may also increase brittleness films. For first time, an additive manufacturing (AM) technology is demonstrated fabricate mechanical strength flexible NC-based efficiently. Different concentrations (10, 20, 30 wt%) lead zirconate titanate (PZT)...
Atomic cooling haloes with virial temperatures $\rm T_{vir} \geq 10^{4}$ K are the most plausible sites for formation of first galaxies and intermediate mass black holes. It is therefore important to assess whether one can obtain robust results concerning their main properties from numerical simulations. A major uncertainty presence turbulence, which barely resolved in cosmological We explore latter both by pursuing high-resolution simulations up 64 cells per Jeans length incorporating a...
Population III stars forming in the infant universe at z=30 heralded end of cosmic dark ages. They are presumed to be assembled so-called minihaloes with virial temperatures a few thousand K where collapse is triggered by molecular hydrogen cooling. A central question concerns their final masses, and whether fragmentation occurs during formation. While studies employing Lagrangian codes suggest via self-gravitating disk, recent high resolution simulations indicated that disk formation...
Radiative feedback produced by stellar populations played a vital role in early structure formation. In particular, photons below the Lyman limit can escape star-forming regions and produce background ultraviolet (UV) flux, which consequently may influence pristine halos far away from radiation sources. These quench formation of molecular hydrogen photodetachment H−. this study, we explore impact such UV on fragmentation massive primordial few times 107 M☉. To accomplish goal, perform high...
The detection of z > 6 quasars reveals the existence supermassive black holes a few 109 M⊙. One potential pathways to explain their formation in infant universe is so-called direct collapse model which provides massive seeds 105–106 An isothermal mandates that haloes should be primordial composition and molecular hydrogen remains suppressed presence strong Lyman Werner flux. In this study, we perform high resolution cosmological simulations for two employing detailed chemical includes H−...
While large numbers of supermassive black holes have been detected at z>6, their origin is still essentially unclear. Numerical simulations shown that the conditions for classical direct collapse scenario are very restrictive and fragmentation difficult to be avoided. We thus consider here a more general case dense massive protostar cluster low metallicity (<~ 10^{-3} Z_solar) embedded in gas. estimate mass central object, formed via collisions gas accretion, considering extreme cases...
Observations of quasars at $\rm z> 6$ report the existence a billion solar mass black holes. Comprehending their formation in such short time scale is matter ongoing research. One most promising scenarios to assemble supermassive holes monolithic collapse protogalactic gas clouds atomic cooling halos with T_{vir} \geq 10^{4} K$. In this article, we study amplification and impact magnetic fields during seed massive primordial halos. We perform high resolution cosmological magnetohydrodynamics...
High redshift quasars at z>6 have masses up to ~$10^9$ M$_\odot$. One of the pathways their formation includes direct collapse gas, forming a supermassive star, precursor black hole seed. The conditions for are more easily achievable in metal-free haloes, where atomic hydrogen cooling operates and molecular (H2) is inhibited by strong external UV flux. Above certain value flux (J_crit), gas halo collapses isothermally ~$10^4$ K provides star formation. However, H2 can self-shield, reducing...
CR7 is the brightest Lyman-α emitter observed at z > 6, which shows very strong and He ii 1640 Å line luminosities, but no metal-line emission. Previous studies suggest that hosts either young primordial stars with a total stellar mass of ∼107 M⊙ or black hole ≳106 M⊙. Here, we explore different formation scenarios for semi-analytical model, based on random sampling dark matter merger trees. We are unable to reproduce observational constraints source, given our model assumptions, due short...
Supermassive black holes are not only common in the present-day galaxies, but billion solar masses also powered $z\geq 6$ quasars. One efficient way to form such is collapse of a massive primordial gas cloud into so-called direct hole. The main requirement for this scenario presence large accretion rates $\rm \geq 0.1~M_{\odot}/yr$ supermassive star. It yet clear how and under what conditions can be obtained. prime aim work determine mass non-isothermal conditions. We perform high resolution...
Baryonic streaming motions produced prior to the epoch of recombination became supersonic during cosmic dark ages. Various studies suggest that such velocities change halo statistics and also influence formation Population III stars. In this study, we aim explore impact on supermassive black holes at $z>10$ via direct collapse scenario. To accomplish goal, perform cosmological large eddy simulations for two halos a few times $\rm 10^{7} M_{\odot}$ with initial 3, 6 9 km/s$. These massive...
Understanding the growth of high redshift massive black holes (MBHs) is a problem great astrophysical interest. The most luminous quasars at $z>6$ are frequently observed but they represent only tip iceberg as majority low luminosity AGN population remains undetected. In present study, we perform radiation hydrodynamics cosmological simulation to study "normal" in universe. our model formation Pop III and II stars along with their chemical, mechanical radiative feedback. We consider both UV...
Massive primordial halos exposed to moderate UV backgrounds are the potential birthplaces of supermassive black holes. In these halos, an initially isothermal collapse will occur, leading high accretion rates ~0.1 M⊙ yr-1. During collapse, gas in interior turn into a molecular state, and form disk order conserve angular momentum. We consider here structure such role viscous heating presence for central star 10, 100, 104 M⊙. Our results show that temperature increases considerably due...