Historical research guide · 0991 · 2012
Deconstructing the Interiors of Compact Stars
Armen Sedrakian
In one minute
A neutron star is the densest object you can point a telescope at: more mass than the Sun packed inside a city, at pressures no laboratory reaches. Nobody can open one up, so the question Armen Sedrakian took to a nuclear-physics symposium in Goa in 2010 is how to take the interior apart from the outside — to deconstruct it — using the few numbers a star will give you: its mass, its radius, its spin, and how fast it cools. This chapter is the written version of that talk. It sits behind a publisher’s paywall with no open copy anywhere, so this page reads the programme from Sedrakian’s own reviews of the same work in the same months. The argument there is that the freshly measured two-solar-mass pulsar rules out anything that softens ultra-dense matter too far, and yet still leaves room inside for hyperons and for a colour-superconducting quark core — provided nuclear matter is stiff above saturation density and the quarks repel each other strongly enough.
Connection
Chapter 13 asks how you build a confident picture of something you cannot open, and compact-star physics is the discipline that does it best: a handful of observed numbers, a candidate equation of state, and everything that fails the numbers thrown away. Chapter 5 gains its natural laboratory, because the interior states under discussion here — superfluid neutrons, colour-superconducting quarks — are macroscopic quantum fluids at nuclear density, the closest thing in nature to the medium that chapter asks the vacuum to be.
From the source
Chapter 17 of the proceedings, pages 162 to 171, sets out to deconstruct the interior of a compact star — that is, to reconstruct what a neutron star is made of from the outside quantities that can be measured. Armen Sedrakian, of the Institute for Theoretical Physics at Goethe University Frankfurt, delivered it at the Symposium on Advances in Nuclear Physics in Our Time in Goa in late 2010, and World Scientific published the volume in 2012.Bibliographic record: chapter 17, pages 162 to 171, event record for the Goa symposium
The measurement of a pulsar of 1.97 plus or minus 0.04 solar masses places a stringent lower bound on the maximum mass of compact stars, and therefore challenges the existence of any agent that softens the equation of state of ultra-dense matter. In compact-star physics a single well-measured mass does more work than a decade of argument, because everything that cannot hold up that mass is eliminated at once.Companion review, Bonanno and Sedrakian, arXiv 1108.0559, Abstract and Section 1
Hyperons and deconfined quark matter can nonetheless be accommodated inside a two-solar-mass star. Stable configurations at or above 1.97 solar masses are obtained, featuring both hypernuclear matter and quark matter, on three conditions: the equation of state of nuclear matter is stiff above the saturation density, the transition to quark matter takes place at a few times nuclear saturation density, and the repulsive vector interactions among the quarks are substantial.Companion review, Sedrakian, Acta Physica Polonica B 5, 867 (2012), Abstract; and arXiv 1108.0559, Abstract
Where quark matter exists in the core, it is in a colour-superconducting state — a macroscopic quantum condensate of quarks, the strong-force analogue of the paired electrons in an ordinary superconductor. The interior of a massive compact star is therefore modelled not as an inert lump of matter but as a layered quantum fluid, hypernuclear above and colour-superconducting below.Companion review, Sedrakian, Acta Physica Polonica B 5, 867 (2012), Abstract and the section on colour superconductivity
The interior is reconstructed rather than seen. The method is to build the equation of state from nuclear theory — a phenomenological relativistic hypernuclear density functional joined to an effective model of quantum chromodynamics of Nambu-Jona-Lasinio type — then keep only those compositions whose stellar configurations survive the observed masses.Companion review, Bonanno and Sedrakian, arXiv 1108.0559, Abstract and model section
Cooling is the second lever, and the open one. How fast the surface of a young neutron star loses heat depends on what its core is made of, so the thermal evolution of massive stars with colour-superconducting quark cores is the measurement that would separate the candidate interiors from each other once the masses have narrowed the field.Companion review, Sedrakian, Acta Physica Polonica B 5, 867 (2012), Abstract, closing sentence on cooling
The way in
https://doi.org/10.1142/9789814355766_0017How to cite it
Armen Sedrakian (2012) Deconstructing the Interiors of Compact Stars doi:10.1142/9789814355766_0017