Stars ’ - Have They Been Discovered ?

Recently there is a suggestion about the star RXJ1856.5−3754, being a possible candidate for quark star. While from the estimates of the radiation radius, given by the authors, it does not seem to fit with any of the known models for such stars, the mass radius diagram admits the possibility of this being a quark star of mass M ⊙ < M < 1.4M ⊙ , provided the radius mentioned is the actual radius of the star. Subject headings: star: RXJ1856.5−3754 – strange star – neutron star – equation of state 1. INTRODUCTION One of the hot topics in astrophysics of late has been the possibility of the discovery of Strange Stars (stars composed of u, d and s quark matters), through X-ray observations from the Chandra satellite by Drake et al., (2002). Though discussions of the possibility of the existence of such stars dates back to the eighties (Witten, 1984 and later by Alcock et al., 1986, Haensel et al., 1986, etc.), with high resolution data from the X-ray observations , recently observers have improved the accuracy for ascertaining the dimensions of the compact objects associated with the observed emissions (Walter et al., 1996 Walter & Mathews 1997 and Pons et al., 2001). During the last few years, there have been several sources, which are considered niether as black holes nor neutron stars, like While it is extremely difficult to come to a conclusion regarding a candidate being a black hole (for masses of the order of few solar masses), it is slightly better for neutron stars, once proper estimates of mass and radius are made along with the evidence for the existence of a hard surface which could produce bursts. The method of obtaining the crucial parameters from observational data do depend upon the models adopted. One of the recent candidates, which has evoked a lot of attention in this context is the source RXJ1856.5−3754, an isolated compact star at a distance of ∼ 140 pc in the outskirts of the R CrA dark molecular cloud (Drake et al., 2002, Campana et al., 1997 and Pons et al., 2002). According to Drake et al., (2002) this investigation, the implied radius of the star seems to be R ∞ ≈ 3.8 − 8.2 km, where R ∞ = R 1 − 2M R (G = c = 1) (1) R being the true radius and M the mass of …