Browsing by Author "Dey, Mira"

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    Astrophysical consequences of diquark formation on the surface of strange star
    (2001-05-12) Dey, Mira; Sinha, Monika; Ray, Subharthi
    Compactness of some stars is explained if they are strange stars (SS) as shown by Dey et al.(1998) (D98) and Li et al. (1999a,b). In D98, a realistic potential was used in a Fock mean eld approximation within Dirac phe- nomenology, thereby simplifying the spinorial structure of the quarks. Using the plane wave states for the beta equi- librated u, d and s quark Fermi seas from D98 and the conventional spin dependent force between these quarks, we now nd energy lowering in some speci c spin-aligned states. This is a short range pairing between quarks of dif- ferent flavours and may lower the energy by several MeV for each diquark pair. The accretion driven X-ray and γ ray bursts in com- pact objects are believed to be due to thermonuclear or some other explosions which are short lived. These may in fact destroy the spin alignment of the quarks if these stars are SS. The subsequent alignment and production of copious diquark pairing may produce su cient energy to produce recurrent very long bursts seen in some such stars. The long time involved in these processes, we claim, is due to the weak interactions which are responsible for the equilibration of strange quark matter. In such a the case the elusive properties of some of the most massive objects in nature, the compact stars, can be accounted for by spin alignment of pairs of the smallest components of matter, - namely the quarks.
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    Density dependent strong coupling constant of QCD derived from compact star data
    (2000-05-16) Ray, Subharthi; Dey, Jishnu; Dey, Mira
    The present work is an endeavour to connect the properties of tiny nearly massless objects with those of some of the most massive ones, the compact stars. Since 1996 there is major influx of X-ray and γ ray data from binary stars, one or both of which are compact objects that are difficult to explain as neutron stars since they contain a mass M in too small a radius R . The suggestion has been put forward that these are strange quark stars (SS) explainable in a simple model with chiral symmetry restoration (CSR) for the quarks and the M, R and other properties like QPOs (quasi periodic oscillations) in their X-ray power spectrum. It would be nice if this astrophysical data could shed some light on fundamental properties of quarks obeying QCD. One can relate the strong coupling constant of QCD, αs to the quark mass through the Dyson-Schwinger gap equation using the real time formalism of Dolan and Jackiw. This enables us to obtain the density dependence of αs from the simple CSR referred to above. This way fundamental physics, difficult to extract from other models like for example lattice QCD, can be constrained from present - day compact star data and may be put back to modelling the dense quark phase of early universe.
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    Possible evidence of surface vibration of realistic strange stars from stellar observations
    (2011-07-05) Ray, Subharthi; Dey, Jishnu; Dey, Mira; et al.
    Emission lines in the eV and keV range by certain stellar candidates from their recent analysis invoke the question of their possible origin. These stars under consideration, are the 4U 0614+091 (0.65, 0.86, and 1.31 keV ), 2S 0918−549 (0.8 keV with width 55 eV ), 4U 1543−624 (0.7 keV ), 4U 1850 −087 (0.7 keV ) and 4U 1820−30 (0.6 and 0.9 keV ) and also the 0.6 keV excess emission in RX J170930.2−263927. Recently, it has been suggested that the resonance absorption at ∼ in 0.7, 1.4, 2.1 and 2.8 keV 1E1207−5209 and 0.35, 0.7 and 1.4 keV RX J1856.5−3754 are due to harmonic surface vibrations in strange stars. We propose that these harmonic vibrations may also responsible for emission lines in the above mentioned compact stellar candidates.
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    Stability of strange stars (SS) derived from a realistic equation of state
    (2002-03-01) Sinha, Monika; Dey, Jishnu; Dey, Mira
    A realistic EOS (equation of state) leads to strange stars (ReSS) which are compact in the mass radius plot, close to the Schwarzchild limiting line [1]. Many of the observed stars fit in with this kind of compactness, irrespective of whether they are X-ray pulsars, bursters or soft γ repeaters or even radio pulsars. We point out that a change in the radius of a star can be small or large, when its mass is increasing and this depends on the position of a particular star on the mass radius curve. We carry out a stability analysis against radial oscillations and compare with the EOS of other SS models. We find that the ReSS is stable and an M-R region can be identified to that effect