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.
We use the densest objects in the universe as laboratories for nuclear physics we can never build on Earth.
A neutron star packs more than the Sun's mass into a sphere the width of a city. Its core reaches several times the density of an atomic nucleus — a regime no accelerator on Earth can reproduce.
That makes every merger LIGO hears, every pulsar NICER times, and every glitch we observe a measurement of nuclear physics. Our work is building the theory precise enough to read those measurements.
Four questions driving the lab
Each one connects a piece of nuclear theory to something a telescope or detector can actually measure.
Phys. Rev. D 99, 123026
How stiff is matter at five times nuclear density?
The equation of state fixes how much mass a neutron star can hold before it collapses. We build relativistic mean-field models of dense nuclear matter and push them against the hard limits set by two-solar-mass pulsars, GW170817's tidal deformability, and NICER's radius measurements.
The models that survive all three tell us something no terrestrial experiment can.
Read more →
Phys. Rev. D 106, 063005
Can we hear a star's interior in how it rings?
A perturbed neutron star oscillates in distinct modes — f, p and g — each carrying a fingerprint of the matter inside it. We compute those frequencies and damping times, then trace which nuclear parameters actually control them.
Next-generation detectors should resolve these modes. We are working out what they will say when they do.
Read more →
MNRAS 525, 5492
What if dark matter is already inside the star?
Neutron stars accrete dark matter over billions of years. If enough accumulates, it changes the star's radius, its tidal response, and the frequency at which it oscillates — all of it observable.
We model admixed configurations and run Bayesian inference against real data to find where the signature would be strong enough to detect.
Read more →
JCAP 04, 065
Do nucleons survive at all in the core?
Deep enough inside, it becomes energetically cheaper to make hyperons, Δ-baryons, or to deconfine into quark matter altogether. Every one of those options softens the equation of state and shifts what the star looks like.
We work out which exotic phases stay consistent with the observations — and which are already ruled out.
Read more →The lab in numbers
Selected results
Figures taken directly from NAP Lab publications. Follow the citation under each one to open the paper.
Who runs the lab
Dr. Bharat Kumar
Department of Physics & Astronomy, NIT Rourkela — since June 2020
Bharat works on the nuclear equation of state and what it implies for compact objects — from relativistic mean-field models of dense matter through to gravitational-wave signatures of neutron star oscillations. He founded NAP Lab in 2020 and supervises its PhD and Masters researchers.
The researchers
Sayantan Ghosh
M.Sc., Banaras Hindu University
Dr. Pinku Routaray
News
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 ↗
Work on adiabatic sound speeds and radial-oscillation stability published in JCAP 09, 025 ↗
Pinku wins Best Poster at the DAE High Energy Physics Symposium, BHU. Event ↗
Upcoming
GWsNS-2026 — Gravitational Waves from Neutron Stars school, Roscoff, France.
AGWAM 2026 — Asian Gravitational Wave Astronomy Meeting, Chiang Mai, Thailand.
Multimessenger Astrophysics 2026 — 9th ICE Summer School, Barcelona, Spain.
Erice School — Neutrinos in Cosmology, Astro-, Particle & Nuclear Physics, Sicily.
Recent publications
Spacetime Curvature as a Probe of Exotic Core Phases in Neutron Stars within Modified Gravity
Observable Signatures of a Quarkyonic Phase in Neutron Stars
The Role of Adiabatic Sound Speeds in Neutron Star Radial Oscillations and Stability
Probing the Impact of Delta-Baryons on Nuclear Matter and Non-Radial Oscillations in Neutron Stars
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 →Contact
Dr. Bharat KumarMC202, Department of Physics & Astronomy
National Institute of Technology, Rourkela
Odisha 769008, India
kumarbh@nitrkl.ac.in
Campus map ↗
Support
Our work is supported by the Science and Engineering Research Board (SERB), Government of India.
NAP Lab is part of the Department of Physics and Astronomy at NIT Rourkela.
