I am a theoretical nuclear astrophysicist working as an associate professor of physics at the Mathematics and Physics of Manhattan University. My research in neutron star astrophysics focuses on the studies of the structure, composition, and dynamics of neutron stars (mass, radii, moments of inertia, tidal deformability, nuclear pasta, cooling processes, gravitational wave emissions, etc.) through developing and employing equations of state of neutron-rich matter. My research in nuclear theory focuses on the understanding of isovector nuclear interaction through building and developing nuclear energy density functionals in the context of the relativistic mean-field and Skyrme Hartree-Fock models, and through studies of the density dependence of the nuclear symmetry energy, neutron, and weak charge distributions, and the neutron skin thicknesses of medium to heavy nuclei. My research publications are on my Google Scholar page or in my NASA Astrophysics Data System.
The rungs of the nuclear density ladder
Laboratory experiments sensitive to the equation of state of neutron-rich matter in the vicinity of nuclear saturation density provide the first rung in a “density ladder” that connects terrestrial experiments to astronomical observations. In this context, the neutron skin thickness of Pb-208 provides a stringent laboratory constraint on the density dependence of the symmetry energy. Exploiting the strong correlation between the neutron skin and the slope of the symmetry energy L within a specific class of relativistic energy density functionals, in collaboration with Brendan T. Reed, Charles J. Horowitz, and Jorge Piekarewicz, we found a value of L=(106±37) MeV—which systematically overestimates current limits based on both theoretical approaches and experimental measurements. The impact of such a stiff symmetry energy on some critical neutron-star observables was also examined. The paper was published in the Physical Review Letters and was chosen as part of the Editor's Suggestion.
Image courtesy of Jorge Piekarewicz, Florida State University
The "BigApple" Equation of State
Is the secondary component of GW190814 the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system? With Chuck Horowitz, Jorge Piekarewicz and Brendan Reed we tried to answer this question on a work that is now published in the Physical Review C. By tuning existing energy density functionals we were able to: (i) account for a 2.6 M⊙ neutron star, (ii) satisfy the original constraint on the tidal deformability of a 1.4 M⊙ neutron star, and (iii) reproduce ground-state properties of finite nuclei. For the class of models explored in our work, we found that the stiffening of the equation of state required to support supermassive neutron stars is inconsistent with either constraints obtained from energetic heavy-ion collisions or from the low deformability of medium-mass stars. Thus, we speculated that the maximum neutron star mass can not be significantly higher than the existing observational limit and that the 2.6 M⊙ compact object is likely to be the lightest black hole ever discovered.
Rapid Neutrino Cooling in the Neutron Star MXB 1659-29
In collaboration led by Prof. Edward F. Brown, we have found that the neutron star MXB 1659-29 is the first neutron star with a firmly detected thermal component in its x-ray spectrum that needs a fast neutrino-cooling process. In particular, we found that it has a core luminosity that substantially exceeds that of a modified Urca reaction and is consistent with the direct Urca reaction operating in a small fraction of the core. We suggested that future measurements of the temperature variation of the neutron star core during quiescence should place an upper limit on the core specific heat and serve as a check of the fraction of the neutron star core in which nucleons are unpaired. The article was published in the Physical Review Letters. It was also chosen as an Editor's Suggestion and featured as a Physics Viewpoint. Several news outlets picked up this story including Science News and Риа Новости.
Neutron Skins and Neutron Stars in the Multi-Messenger Era
In collaboration with Prof. Jorge Piekarewicz and Prof. Charles J. Horowitz we used the GW170817 data on tidal deformability to constain the canonical neutron star radius to be less than 13.8 km and the corresponding neutron skin thickness of Pb-208 to be less than about 0.25 fm. The paper is published in the Physical Review Letters and was chosen as an Editor's Suggestion as well as was featured as a Physics Synopsis. Many news outlets picked up the story including Physics World and Inside Science.
Caption for Figure on the right: Neutron stars properties and neutron skins are connected through sharing the same physics of strong nuclear interaction that predicts the pressure of neutron-rich dense matter.
Deep Crustal Heating by Neutrinos
We have recently presented a new mechanism of heating the inner crust of accreting neutron stars, where we used a novel idea that charged pions produced during nuclear collisions decay and provide a flux of neutrinos that travel towards the inner region of the crust. In particular, we find that for massive and compact neutron stars neutrinos can deposit as large as 2 MeV energy per an accreted nucleon. This paper is published in the Physical Review C.
Large Volume Quantum Simulations of Nuclear Pasta
We demonstrated the first large volume microscopic quantum calculations of nuclear pasta, which is published in the Physical Review C. In particular, we studied the role of the density dependence of the nuclear symmetry energy and found that depending on the density slope of the symmetry energy various nuclear pasta phases may form in neutron stars crust. The effect was insignificant in the case of supernova matter.
From left to right: gnocchi, spaghetti, and lasagna phases. The figure is taken from our paper published in the Phys. Rev. C 95, 055804 (2017).