NDLI: Equation of state of dense nuclear matter and an upper bound on neutron star masses

Content Provider	Springer Nature Link
Author	Negi, P.S. Durgapal, M.C.
Copyright Year	2001
Abstract	We have discussed, in general, the important physical parameters, likemaximum mass, radius, and the minimum rotation period of self-bound,causally consistent, and pulsationally stable neutron stars (Q-starmodels) by using a realistic stiff EOS (such that, the speed of sound,v∝ P N, or nP=K(E-E a ) n, where K≤ 1 and n =1/(1-2N);where P and E represent respectively, the pressure and theenergy-density, and E a is the value of E at the surface (r = a) of the configuration) within the two constraints imposed by: (i) The minimumrotation period, P rot, for the pulsar known to date corresponds to1.558 ms, and (ii) The maximum number density anywhere inside thestructure for the models described as Q-stars cannot exceed ∼ 1nucleon/fm3. By using the empirical formula given by Koranda,Stergioulas and Friedman (1997) (KSF-formula), and imposing constraint(i), we have obtained an upper bound of M max ≅ 7.76 M ⊙radius a≅ 32.5 km, and the central energy-density around 2.17 ×1014 g cm-3 (for n =1.01). Constraint (ii) provides the minimumrotation period, P rot ∼ 0.489 ms for the maximum mass M max∼ 2.4 M⊙, and the central energy-density around 2.20 ×1015 g cm-3 (for n =1.01). The speed of sound at the centre ofthese models approaches ∼ 99% of the speed of light `c' (in thevacuum) and vanishes at the surface of the configuration together withpressure. If we relax the maximum Kepler frequency imposed by the fastestrotating pulsar known to date (constraint (i)), in view of certainobservational effects and theoretical evidences, and allow the present EOSto produce larger rotation rates than the 1.558 ms pulsar, the maximummass of the non-rotating model drops down to a value ∼ 7.2 M ⊙.The higher values of masses (≥ 7 M ⊙) and radii (∼31-32 km) obtained in this study imply that these models may representthe massive compact objects like Cyg X-1, Cyg XR-1, LMC X-3, and otherswhich are known as black hole candidates (BHCs). This study also suggestthat the strongest contender for black hole at present might be recurrentnova V404 Cyg (mass estimate ∼ 8 -12 M ⊙).
Starting Page	299
Ending Page	318
Page Count	20
File Format	PDF
ISSN	0004640X
Journal	Astrophysics and Space Science
Volume Number	275
Issue Number	3
e-ISSN	1572946X
Language	English
Publisher	Kluwer Academic Publishers
Publisher Date	2001-01-01
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Astronomy
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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