Reading the physics of matter at its limit.
Inside a neutron star, matter is squeezed past anything we can make on Earth. At the National Institute of Technology, Rourkela we build the nuclear models — and test them against gravitational waves, pulsar timing and X-ray data — to work out what that matter actually is.
From finite nuclei to gravitational waves
The same nuclear force that binds a finite nucleus also supports a neutron star. We construct relativistic mean-field interactions — G3, IOPB-I, and NITR — fitted to nuclear masses, radii and saturation properties, then use that equation of state for the stellar structure problem. The question is whether a model that describes nuclei still satisfies the two-solar-mass pulsar limit and the tidal deformability measured in GW170817.
Many neutron-star observables are tightly correlated. A single tidal measurement can therefore be turned, through EoS-insensitive relations, into bounds on radius and on the moment of inertia of PSR J0737−3039A. In that sense a gravitational-wave event is a nuclear-physics experiment, provided the theory connecting the two is under control.
Oscillation modes are a second window on the same physics. f- and p-mode frequencies, computed in the Cowling approximation and in linearized general relativity, track nuclear parameters such as the slope of the symmetry energy. Universal relations between quasinormal modes and tidal deformability give a handle that does not lean on any one equation of state.
The core need not be purely nucleonic. Hyperons and Δ-baryons soften the equation of state and shift the spectrum; a second fluid of WIMP or fermionic dark matter does the same. Those shifts have been compared with GW170817 posteriors and with compact objects such as PSR J0952−0607. Figures from the papers, and the full list, are on the publications page.
Open problems we are working towards
Six questions at the edge of what neutron-star data and dense-matter theory can answer today. Each is a starting point for a PhD, postdoc or master’s project; none is a finished result.
Can f-mode universality tell dark matter from nuclear softening?
Dark-matter admixture, hyperons and Δ-baryons all soften the equation of state, so mass–radius and tidal data alone cannot separate them. Universal relations (f-mode–tidal, I-Love-Q) are calibrated on single-fluid stars; in two-fluid stars they may bend in a way that is specific to dark matter.
First step. Build a two-fluid f-mode solver and map how far dark-matter core and halo configurations leave the single-fluid universal band, across RMF families.
- Two-fluid TOV
- Cowling / full GR modes
- G3 · IOPB-I · NITR
GW170817 at ten years: a nuclear-physics-first posterior
Most EoS inference uses piecewise or spectral parametrisations that forget the nuclear Lagrangian. Sampling the RMF couplings directly, with NICER and the O4 neutron-star events, would turn each new detection into a bound on L₀, K₀ and the symmetry-energy curvature.
First step. Re-run the joint LVK + NICER likelihood with RMF couplings as the sampled parameters and compare the posterior on L₀ with finite-nuclei constraints.
- Bayesian inference
- NICER pulse-profile posteriors
- LVK public data
Proto-neutron-star modes as a clock for core-collapse gravitational waves
The f- and g-mode frequency of a cooling proto-neutron star sweeps upward in time. Mapping that track to temperature, entropy and lepton fraction would turn a Galactic supernova signal into a measurement of finite-temperature EoS physics.
First step. Extend the finite-T non-radial oscillation calculation to evolving snapshots and produce a frequency-versus-time template band for Einstein Telescope and Cosmic Explorer sensitivity.
- Finite-T RMF EoS
- Non-radial modes
- 3G detector noise curves
Slow conversion and slow-stable stars: do they leave a GW fingerprint?
When the quark–hadron conversion timescale is long compared with an oscillation period, the radial spectrum and the stability boundary change. Whether this shifts post-merger or ringdown frequencies measurably is unexplored.
First step. Quantify the shift of the radial-mode frequency with conversion rate for slow-stable hybrid stars and check which part of it survives in the observable f-mode.
- Radial oscillations
- Hybrid EoS
- Twin-star branches
Modified gravity or exotic core? Curvature invariants as a discriminator
Energy-momentum-squared gravity and a stiff or softened core can produce nearly the same mass–radius curve. Interior curvature and the trace anomaly respond differently to each, but whether that difference reaches any observable is open.
First step. Find pairs of (EoS, gravity) models with identical M–R and tidal curves, then compute where their oscillation spectra and curvature profiles part ways.
- EMSG
- Trace anomaly
- Universal relations
Do dark-matter cores change the r-mode instability window?
Rotating, magnetised dark-matter admixed stars have been built, but their dissipation and the r-mode growth timescale have not. A dark-matter component could move the instability boundary that limits millisecond-pulsar spin.
First step. Add the dark-matter fluid to the r-mode growth and damping timescales and compare the spin-frequency ceiling with observed fast pulsars.
- Slow-rotation formalism
- Viscous damping
- Pulsar spin catalogues
Have your own idea that fits? Write with a paragraph on it — we are happy to consider it.
The researchers
Subha Mitra
M.Sc., University of Calcutta
Sayantan Ghosh
M.Sc., Banaras Hindu University
Dr. Pinku Routaray
News
Sayantan Ghosh defends his PhD thesis. He joined the lab in July 2022 and worked on quasinormal modes of neutron stars.
Subha Mitra joins the group as a PhD researcher. M.Sc., University of Calcutta.
Pinku Routaray defends his PhD on “Dark Matter Effects on Neutron Star Structure and Observables”, and moves to the Kavli Institute for Astronomy and Astrophysics, China, as a postdoctoral fellow.
New paper on spacetime curvature as a probe of exotic core phases in modified gravity — Phys. Rev. D 113, 024070 ↗
Latest in neutron-star & GW astrophysics
Fetched live in your browser. Preprints come from INSPIRE HEP (arXiv); published papers come from Crossref for the APS, AAS and other journals. Nothing here is hand-written.
Also: arXiv:astro-ph.HE ↗, nucl-th ↗, Phys. Rev. D ↗, ApJ ↗, LIGO News ↗
Upcoming conferences & schools
Neutron stars, dense matter, nuclear astrophysics and gravitational waves. The list updates itself: finished meetings drop off, new ones are pulled from INSPIRE HEP.
PhD & postdoc positions worldwide
Open calls in our research field. Posts disappear on their deadline; new ones appear from INSPIRE HEP jobs and a weekly-refreshed curated list. Always confirm details on the advertiser’s page.
Join the lab
We take students and postdocs who want to work at the boundary between nuclear theory and observational astrophysics. Prior experience with numerical methods helps; curiosity matters more.
PhD Fellowship — DST WISE
Projects in neutron-star asteroseismology, dark-matter admixed stars, and multi-messenger constraints on the equation of state.
Apply via DST WISE →SERB National Postdoctoral Fellowship
Postdoctoral work in nuclear astrophysics, gravitational-wave oscillation modes, or EoS inference from LIGO and NICER data.
Apply via SERB →Bring your own fellowship
Already hold external funding, or planning to apply? Write with a short note on what you want to work on and we will take it from there.
kumarbh@nitrkl.ac.in →Codes & tools
General-relativistic structure and oscillation codes used in the lab. Repositories live under the lab GitHub.
TOV Solver & compact-common
General-relativistic TOV integration code for computing mass-radius relations, tidal deformabilities, and moment of inertia for arbitrary EoS tables.
GitHub ↗Oscillation Mode Solver
Radial and non-radial oscillation mode calculation (f-, p-, w-modes) using Cowling approximation and full GR perturbation equations.
GitHub ↗Two-Fluid Dark Matter TOV
Modified TOV solver for dark matter admixed neutron stars. Supports WIMP and fermionic dark matter with varying interaction cross-sections.
GitHub ↗Contact
Dr. Bharat Kumar
Assistant Professor · Physics & Astronomy
MC202, Department of Physics & Astronomy
National Institute of Technology, Rourkela
Odisha 769008, India
Campus map ↗ Google Scholar ↗ Faculty page ↗
Affiliation & support
NAP Lab is part of the Department of Physics and Astronomy at NIT Rourkela. The work is supported by the Science and Engineering Research Board (SERB), Government of India.
