Constraining properties of neutron stars with heavy–ion reactions

Bao–An Li*, Lie–Wen Chen,** Che Ming Ko*** and A.W. Steiner****

* Department of Chemistry and Physics, P.O. Box 419, Arkansas State University, State University, AR 72467–0419, U.S.A.

** Institute of Theoretical Physics, Shanghai Jiao Tong University, Shanghai 200240, and Center of Theoretical Nuclear Physics, National Laboratory of Heavy–Ion Accelerator, Lanzhou, 730000, China.

*** Cyclotron Institute and Physics Department, Texas A & M University, College Station, Texas 77843, U.S.A.

**** Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A.

Recibido el 19 de enero de 2006
Aceptado el 24 de julio de 2006

Abstract

Nuclear reactions induced by stable and/or radioactive neutron–rich nuclei provide the opportunity to pin down the equation of state of neutron–rich matter, especially the density (ρ) dependence of its isospin–dependent part, i.e., the nuclear symmetry energy E_sym. A conservative constraint, 32(ρ/ρ₀)^0.7 < E_sym(ρ) < 32 (ρ /ρ₀)^1.1, around the nuclear matter saturation density ρ₀ has recently been obtained from the isospin diffusion data in intermediate energy heavy–ion collisions. We review this exciting result and discuss its consequences and implications on nuclear effective interactions, radii and cooling mechanisms of neutron stars.

Keywords: Neutron stars; nuclear reaction models; equation of state.

Resumen

Se puede determinar la ecuacion de estado de materia con exceso de neutrones usando reacciones nucleares inducidas por haces estables y radioactivos de núcleos con exceso de neutrones, en particular cómo depende la contribución del iso–espín, es decir la energía de simetría nuclear E_sym, de la densidad (ρ). Recientemente, se obtuvo una restricción conservadora, 32 (ρ/ρ₀)^0.7 < E_sym(ρ) < 32 (ρ /ρ₀)^1.1 cerca de la densidad de saturación de la materia nuclear ρ₀ de los datos experimentales para la difusión de iso–espín en colisiones de iones pesados a energías intermediarias. Se presenta una revisión de este resultado alentador y se discuten sus consecuencias e implicaciones para interacciones efectivas nucleares, radios y mecanismos de enfriamiento de estrellas de neutrones.

Descriptores: Estrellas de neutrones; modelos de reacciones nucleares; ecuación de estado.

PACS: 26.60.+c; 24.10.–i

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Acknowledgments

This Work work was supported in part by the US National Science Foundation under Grant No. PHYS–0354572 and PHYS–0456890, and the NASA–Arkansas Space Grants Consortium award ASU15154 (BAL); National Natural Science Foundation of China under Grant No. 10105008 and 10575071 (LWC); the US National Science Foundation under Grant No. PHY–0457265 and the Welch Foundation under Grant No. A–1358 (CMK); and the US Department of Energy under grant No. DOE/W–7405–ENG–36 (AWS).

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