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(x), 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 to calculate the detailed properties of SN’s ejecta.
I eagerly anticipate the groundbreaking research opportunities that will result from studying high-redshift SNe (z>3) using cutting-edge telescopes like JWST, ROMAN, and LSST.
I am also thrilled about the potential for groundbreaking discoveries through the next generation of gravitational waves by (LISA).
I use hydrodynamic simulations (& GRMHD) on supercomputers to study microphysics, interactions, and nuclear reactions of nuclear burning, and compact object mergers (e.g., Binary NS, BH-NS/WD, WD-NS/WD).
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.
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. Heavy Element formation
This paper shows that the Milky Way’s heavy elements were not produced by a single astrophysical source. Using stellar abundance data and a chemical-evolution model, we find that the observed behavior of Sr, Y, Ba, and Eu requires three distinct enrichment channels: a prompt source that mainly produces first-peak elements, a delayed r-process channel dominated by binary neutron-star mergers that supplies most of the Galaxy’s europium, and a later AGB s-process contribution that drives the rise of Sr and Y at high metallicity. These results provide new quantitative constraints on the timescales, rates, and nucleosynthetic fingerprints of the astrophysical sites responsible for the origin of the heavy elements.
Left: SAGA database stellar data (MW stars in grey and dwarf galaxies in color) of [Y/Eu] vs [Eu/H]. We plot (blue lines) the fiducial three-channel model presented in this work, with contributions from the r and s processes.
Right: [Y/Eu] versus [Y/Ba] for MW (gray) and dwarf galaxies (color), overlaid with the fiducial one-zone chemical-evolution track. Markers indicate cosmic time along the model trajectory. Early times reflect increased prompt contribution (channel~A) to the first peak production; intermediate times move toward a more Eu-rich mixture as the delayed BNS channel~B becomes important; and late times deviate as AGB s-process enrichment (channel~C) modifies Y and Ba relative to Eu.
B. Double White Dwarfs and SN Ia
B.1 The thermal evolution of the central star in Pa 30:
We modeled the hot central star of Pa 30, the remnant associated with the historical SN 1181, to understand how it evolved into its current extreme state. Our results favor a scenario in which the system formed through the merger of two white dwarfs, leaving behind a massive core and a small hot envelope after a low-energy explosion.
From left to right, top to bottom: 87h of data at 3000mm,
©Akash - 100h of data at 800mm, ©Nicolas - final DSC image
with 560h of exposure in Sii (blue), ©DSC - 1h40 of data with
Hiltner 2.4 m telescope, ©Robert A. Fesen et al.
B2. Double white dwarfs in the Rubin/LSST era:
In this work, we developed a forward-modeling framework that shows that Rubin/LSST should be able to discover at least 287 short-period double white dwarfs via Doppler beaming, including 47 systems that should also be detectable by LISA. This opens a new path for finding compact binaries and using them to test how close binary stars evolve.
B.3 A rare DA+DQ white dwarf binary: We reported the discovery of SDSS J090618.44+022311.6, a rare binary made of two white dwarfs, including a carbon-bearing DQ component. By combining spectroscopy, photometry, and radial-velocity modeling, we showed that the system has a 31.17-hour orbit and provides a valuable clue to the mass-transfer history of compact binary evolution.
Left: Color–magnitude diagram for stars within 100 pc of the Sun. Our target is marked in green. The sequence in the lower left is the normal WD track. We show the cooling curve for a 0.6 M⊙ WD from A. Bédard et al. (2020). Right: Cartoon of two close WDs in binary systems.
B.4 Normal or transitional? Two Type Ia supernovae in Virgo:
This study presents detailed observations of two nearby Type Ia supernovae in the Virgo cluster and shows that one is an intrinsically red but otherwise normal event, while the other lies near the boundary between normal and transitional supernovae. The main result is that spectroscopy near peak brightness is essential for identifying these borderline cases and for building cleaner samples for precision cosmology
C.5 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. 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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