Temperature profiles of accretion discs around rapidly rotating strange stars in general relativity: A comparison with neutron stars

¹ Joint Astronomy Program, Indian Institute of Science, Bangalore 560012, India
² Indian Institute of Astrophysics, Bangalore 560 034, India e-mail: sudip@physics.iisc.ernet.in; sudip@iiap.ernet.in
³ Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune 411 007, India e-mail: arun@iucaa.ernet.in
⁴ Dipartimento di Fisica "E. Fermi" Universitá di Pisa, and INFN Sezione di Pisa, via Buonarroti 2, 56127 Pisa, Italy e-mail: bombaci@df.unipi.it

Corresponding author: S. Bhattacharyya, arun@iucaa.ernet.in

Received: 3 April 2001
Accepted: 12 April 2001

Abstract

We compute the temperature profiles of accretion discs around rapidly rotating strange stars, using constant gravitational mass equilibrium sequences of these objects, considering the full effect of general relativity. Beyond a certain critical value of stellar angular momentum (J), we observe the radius (r_orb) of the innermost stable circular orbit (ISCO) to increase with J (a property seen neither in rotating black holes nor in rotating neutron stars). The reason for this is traced to the crucial dependence of on the rate of change of the radial gradient of the Keplerian angular velocity at r_orb with respect to J. The structure parameters and temperature profiles obtained are compared with those of neutron stars, as an attempt to provide signatures for distinguishing between the two. We show that when the full gamut of strange star equation of state models, with varying degrees of stiffness are considered, there exists a substantial overlap in properties of both neutron stars and strange stars. However, applying accretion disc model constraints to rule out stiff strange star equation of state models, we notice that neutron stars and strange stars exclusively occupy certain parameter spaces. This result implies the possibility of distinguishing these objects from each other by sensitive observations through future X-ray detectors.