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Understanding the dense matter equation of state at extreme conditions is an important open problem. Astrophysical observations of neutron stars promise to solve this, with NICER poised to make precision measurements of mass and radius for…

High Energy Astrophysical Phenomena · Physics 2019-03-20 S. K. Greif , G. Raaijmakers , K. Hebeler , A. Schwenk , A. L. Watts

We have simulated the X-ray polarization data that can be obtained with the Imaging X-ray Polarimetry Explorer, when observing accretion-powered millisecond pulsars. We estimated the necessary exposure times for SAX J1808.4$-$3658 in order…

High Energy Astrophysical Phenomena · Physics 2021-02-03 Tuomo Salmi , Vladislav Loktev , Karri Korsman , Luca Baldini , Sergey S. Tsygankov , Juri Poutanen

Measuring the spin of Accreting Neutron Stars is important because it can provide constraints on the Equation of State of ultra-dense matter. Particularly crucial to our physical understanding is the discovery of sub-millisecond pulsars,…

High Energy Astrophysical Phenomena · Physics 2011-01-28 Alessandro Patruno

Abridged) We model the X-ray properties of millisecond pulsars (MSPs) by considering hot spot emission from a weakly magnetized rotating neutron star (NS) covered by an optically-thick hydrogen atmosphere. We investigate the limitations of…

Astrophysics · Physics 2009-11-13 Slavko Bogdanov , Jonathan E. Grindlay , George B. Rybicki

We develop a new method to measure neutron star parameters and derive constraints on the equation of state of dense matter by fitting the frequencies of simultaneous Quasi Periodic Oscillation modes observed in the X-ray flux of accreting…

High Energy Astrophysical Phenomena · Physics 2020-09-02 Andrea Maselli , George Pappas , Paolo Pani , Leonardo Gualtieri , Sara Motta , Valeria Ferrari , Luigi Stella

Neutron stars provide a compelling testing ground for gravity, nuclear dynamics, and physics beyond the Standard Model, and so it will be useful to locate the neutron stars nearest to Earth. To that end, we revisit pulsar distance estimates…

High Energy Astrophysical Phenomena · Physics 2026-02-24 Joseph Bramante , Katherine Mack , Nirmal Raj , Lijing Shao , Narayani Tyagi

Driven by recent laboratory experiments and astronomical observations, significant advances have deepened our understanding of neutron-star physics. NICER's Pulse Profile Modeling has refined our knowledge of neutron star masses and radii,…

Nuclear Theory · Physics 2024-11-07 Marc Salinas , Jorge Piekarewicz

The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass…

High Energy Astrophysical Phenomena · Physics 2016-12-01 Zach Medin , Marina von Steinkirch , Alan C. Calder , Christopher J. Fontes , Chris L. Fryer , Aimee L. Hungerford

One of the primary goals of Neutron Star Interior Composition Explorer (NICER)-like X-ray missions is to impose stringent constraints on the neutron star equation of state by precisely measuring their masses and radii. NICER has recently…

Neutron stars are not only of astrophysical interest, but are also of great interest to nuclear physicists, because their attributes can be used to determine the properties of the dense matter in their cores. One of the most informative…

The NICER collaboration recently published a joint estimate of the mass and the radius of PSR J0030+0451, derived via X-ray pulse-profile modeling. Raaijmakers et al. (2019) explored the implications of this measurement for the dense matter…

High Energy Astrophysical Phenomena · Physics 2020-04-20 G. Raaijmakers , S. K. Greif , T. E. Riley , T. Hinderer , K. Hebeler , A. Schwenk , A. L. Watts , S. Nissanke , S. Guillot , J. M. Lattimer , R. M. Ludlam

Pulse profile modelling is a relativistic ray-tracing technique that has provided constraints on parameters, with a focus on mass and radius, of five rotation-powered millisecond pulsars. While the technique can also be applied to…

High Energy Astrophysical Phenomena · Physics 2026-01-23 Bas Dorsman , Tuomo Salmi , Anna L. Watts , Mason Ng , Anna Bobrikova , Vladislav Loktev , Juri Poutanen , Joern Wilms

Neutron stars provide a natural laboratory for studying the properties of dense nuclear matter under extreme conditions. In this proceeding, we review our current understanding of dense isospin symmetric and asymmetric matter and neutron…

Nuclear Theory · Physics 2025-04-01 Rajesh Kumar , Veronica Dexheimer , Johannes Jahan

Recent developments in the theory of pure neutron matter and experiments concerning the symmetry energy of nuclear matter, coupled with recent measurements of high-mass neutron stars, now allow for relatively tight constraints on the…

Solar and Stellar Astrophysics · Physics 2016-04-20 James M. Lattimer , M. Prakash

The pulsed X-ray emission from the neutron star surface acts as a window to study the state of matter in the neutron star interior. For accreting millisecond pulsars, the surface X-ray emission is generated from the `hotspots' formed due to…

High Energy Astrophysical Phenomena · Physics 2025-05-20 Pushpita Das , Tuomo Salmi , Jordy Davelaar , Oliver Porth , Anna Watts

The equation of state of dense matter determines the structure of neutron stars, their typical radii, and maximum masses. Recent improvements in theoretical modeling of nuclear forces from the low-energy effective field theory of QCD has…

Nuclear Theory · Physics 2019-09-04 Jeremy W. Holt , Yeunhwan Lim

The Neutron star Interior Composition ExploreR (NICER) is expected to launch in early 2017 and will gather X-ray data on neutron stars and other high-energy sources from a berth on the International Space Station. Its prime scientific goal…

High Energy Astrophysical Phenomena · Physics 2016-05-25 M. Coleman Miller

The double pulsar J0737--3039 has become an important astrophysical laboratory for testing fundamental physics. Here we demonstrate that the low measured mass of Pulsar B can be used to constrain the equation of state of neutron star matter…

Astrophysics · Physics 2009-11-13 Ph. Podsiadlowski , J. D. M. Dewi , P. Lesaffre , J. C. Miller , W. G. Newton , J. R. Stone

The properties of matter at ultra-high densities, low temperatures, and with a significant asymmetry between protons and neutrons can be studied exclusively through astrophysical observations of neutron stars. We show that measurements of…

High Energy Astrophysical Phenomena · Physics 2010-02-16 Feryal Ozel , Dimitrios Psaltis

We determine an empirical dense matter equation of state from a heterogeneous dataset of six neutron stars: three type I X-ray bursters with photospheric radius expansion, studied by Ozel et al., and three transient low-mass X-ray binaries.…

High Energy Astrophysical Phenomena · Physics 2015-05-18 Andrew W. Steiner , James M. Lattimer , Edward F. Brown