Research

For my list of publication click here

I started my research career as a Ph. D student in early 2000s at the Harish-Chandra Research Institute Allahabd (now Prayagraj) in the state of UP (INDIA). After going through a course work for almost two years, I selected my field of specialization Astronomy & Astronomy. For almost next two decades I worked in almost all major areas - computational, observation & theoretical. I have also published 100+ papers in peer review journals with my collaborators. In particular, I have worked in Cosmology (Large Scale Structure, Cosmic Microwave Background & Early Universe), Radio Astronomy (Radio transient detection, H21 mapping, software design & data analysis) and Gravitational Waves. My role in Gravitational Waves has been mostly setting up and managing High Performance Computing systems (Grid Computing) and testing and deploying data analysis pipelines, along with these activities I have contributed in scientific issues also. I was an active member of the LIGO Scientific Collaboration between 2012 and 2018 and visited major LIGO labs in USA and participated in many scientific activities in India and abroad.

Some of the major scientific problems I have worked on are summarized below.

Large Scale Structure of the Universe

In the standard model of the origin and evolution of the Universe (called the Big Bang Theory), the Universe originated from a singularity around 13.7 billion years ago, and since then it has been expanding and cooling. The expanding model of the Universe is strongly supported by many observations, including redshifting of light coming from distant galaxies (which is interpreted as the expansion of the Universe), the presence of the Cosmic Microwave Background Radiation or CMBR (which is interpreted as the fossil radiation of the hot past of the Universe), the chemical abundance of light elements like H, D, Li, and He (which confirms the models of nucleosynthesis in the framework of the Big Bang Theory), and the distribution of galaxies in the local Universe. Apart from the above, other observations show that the energy of the Universe is dominated by a form of matter which does not radiate (called dark matter) and a form of energy which accelerates the expansion of the Universe by producing repulsive gravity (called dark energy).

Observations show that the early Universe was devoid of structures like galaxies, clusters of galaxies, etc. However, there were small fluctuations present in the matter (signatures of which can still be found in the form of CMBR anisotropies) which amplified due to gravity and gave rise to galaxies, clusters of galaxies, and other structures that we see in the local Universe. One of the outstanding problems in cosmology which remains unsolved is to precisely understand how the amplification of the primordial fluctuations took place in the framework of the Big Bang model.

The growth of primordial density perturbations by gravitational amplification is a nonlinear process, and so it is not a surprise that it cannot be modeled analytically. So far, most of the progress in this direction has been made using numerical models or by simulating the gravitational clustering of matter (most of which is dark) called the Cosmological N-body simulations. In a typical N-body simulation, we evolve the trajectories of a very large number of particles (which represent the matter distribution) in an expanding background by solving dynamical equations (Poisson's equation, Newton's equation, etc.) numerically. One of the projects on which I worked for my Ph.D. thesis was to understand the effects of perturbations (fluctuations) on one scale on the growth of the perturbations at other scales, i.e., mode coupling. Another project on which I worked for my Ph.D. thesis was to understand the effects of finite volume in cosmological N-body simulations. A brief summary of the above two projects is as follows.

  1. Role of substructure

    2. As mentioned above, the major component of the universe, known as dark matter, does not interact with photons but plays an important role in the gravitational clustering of normal matter, resulting in the formation of visible structures like galaxies and clusters of galaxies. Dark matter particles (about which we know very little!) can be considered hot or cold based on whether they cluster at very small scales or not. Currently, most observations support the models with cold dark matter, in which matter clustering occurs at small scales first and then progresses towards larger scales in a hierarchical manner. Since in cold dark matter models, small scale perturbations collapse first, it is relevant to ask what role these perturbations play in the collapse of perturbations at larger scales. It is well known that in nonlinear gravitational clustering, small scale perturbations do not significantly affect larger scale perturbations at the level of power spectrum. In one of my projects, I attempted to understand if there are other effects of small scale perturbations or substructures on the collapse of large scale perturbations. The results of various studies carried out under this project have been published in the following publications.

    • Bagla, J. S., Prasad, Jayanti and Ray, Suryadeep, 2005, MNRAS, 360, 194, ( astro-ph/0408429 ) Gravitational collapse in an expanding background and the role of substructure I: Planar collapse
    • Bagla, J. S., Prasad, Jayanti 2008, MNRAS, 1365, 2966 ( arXiv:0802.2796 [astro-ph] ), Gravitational collapse in an expanding background and the role of substructure II: Excess power at small scales and its effect of collapse of structures at larger scales.

  2. Finite volume effects in cosmological N-body simulations

    3. In order to model gravitational clustering cosmological N-body simulation simulate a finite volume of the universe and assume that it is a fair representative of the universe, which may be infinite. This means that in cosmological N-body simulation initial fluctuations at scales larger than the simulation box size are ignored. I tried to understand how various measures of gravitational clustering are affected by the finite volume of the cosmological simulations. The results of the study were published in the following publications.
    • Bagla, J. S., Prasad, Jayanti , 2006, MNRAS, 370, 993, ( astro-ph/0601320), Effects of the size of cosmological N-Body simulations on physical quantities -- I: Mass Function
    • Prasad, Jayanti 2007, J. Astrophys.Astron. 28, 117 ( astro-ph/0702557 ), Effects of the size of cosmological N-Body simulations on physical quantities -- II: Halo Formation and Destruction rate
    • J.S. Bagla, Jayanti Prasad, Nishikanta Khandai 2009, MNRAS,395,2 ( arXiv:0804.1197 [astro-ph]), Effects of the size of cosmological N-Body simulations on physical quantities - III: Skewness.

You can read more about my research in Astronomy & Astrophyics here