### Research

I work on binary systems made of Neutron Stars (NS) and NS/ White Dwarfs

(WD)/Black Holes (BH), as well as double WD systems and core-collapse of massive, rapidly rotating stars. I study how compact objects form, evolve and merge and which transient events they produce. Also, I am interested in magnetic helicity, which plays a significant role in suppressing the kinematic large-scale dynamo driving the large-scale dynamo through the magnetic helicity flux.

Hypotheses are tested using extensive hydrodynamical, thermonuclear, AMR, and multidimensional simulations coupled with detailed nuclear reaction networks (The computational requirements for these use MESA and FLASH). The results of these simulations are followed by an analysis of composition using a large-scale nucleosynthetic network – (PPN). These enable us just to calculate the detailed properties of SN’s ejecta.

I study turbulent nuclear burning, which can largely enhance nuclear burning rates and may serve as an additional mechanism for stellar explosions. Moreover, it may power thermonuclear and pair-instability supernovae, liberate the neutrinos in core-collapse supernovae, and synthesize r-process heavy nuclei in kilonovae and collapsars.

At the moment, I am researching the processes involved in forming low-mass neutron stars in NS-BH systems and the merging of these systems (BH-NS).

Furthermore, I am studying the dynamic ejection of material from binary neutron star systems, including its evolution, characteristics, and outcomes, using 3D GRMHD simulation (e.g., HARM3DNUC).

I am also delving into the fundamental physics behind the failed detonation in high-mass WDs.

Additionally, studying the low-mass BH formation from Dark Matter (DM)- triggered collapse.

Selected Research:

A. BH-NS low mass: BHNS binaries are among the promising compact object mergers. They contribute to the emerging field of multi-messenger astrophysics and rapid transients, producing significant gravitational waves and potentially electromagnetic counterparts, including GRBs. We were studying the mechanism of losing mass dynamically in the BH-NS binary system, including complex mass transfer, gravitational radiations, differential mass ratio, and range of the initial semi-major axis. We illustrate the initial NS mass vs. final mass for dM/M = 1/1000 (stars), 1/100 (circles), and 3/100 (diamonds) and for BH mass = 2.8M_sol (yellow), 3.3M_sol (orange) and 5.0 M_sol (blue) when dM/M = 1/1000, the total mass-loss is so tiny that the points for both black hole masses are superposed at M_(NS,f) ~ M_(NS,0).

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B. BNS simulation: Left panel: The BNS (m1/m2=1) inspiral motion, log density (in x-y) evolution until ~22 msec. The green dots are the tracer particles of BNS, and the BH formed close to 16.65 msec. Right panel: Post-merger of the system (x-z log density) until ~88msec.

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C. The Ca-rich SNe: Left panel: The bolometric light curve of fca1 (green curve), fca2 (blue curve), fca3 (red curve) compared to Ca-rich SNe 2019ehk (squares), 2021gno (circles), and 2021inl (polygons). Right panel: comparison of the three models in the r-band Mr to type Ib/IIb SNe and SN 2019ehk relative to maximum light in the AB magnitude system.

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D. Background Fluctuation: Upeer: Log-log plot of the dimensionless fractional turbulent enhancement in the nuclear burning rate as a function of the RMS temperature fluctuation on length scale r, normalized to the mean temperature, in the distributed burning regime. The curves shown are for neutrino cooling via the "URCA" process (solid line), C12 -C12 burning (dashed), and triple-alpha reaction (dot-dashed). The inset figure shows the same three curves on the same set of axes, compensated by the factor (1/[n*(n - 1)]). For weak enhancement, the compensated enhancement collapses onto a single curve, demonstrating its universal nature. Bottom: the two slices depicting the temperature (left) and nuclear burning rate (right) within three-dimensional simulations of turbulent nuclear burning. The zoomed-in regions highlight the region of the most rapid nuclear burning. The relatively modest turbulent fluctuations lead to large enhancements in nuclear burning, accurately captured in this new theoretical work. (Figure from Fisher+2019, with permission from IOP).