Search for chaos in neutron star systems: Is Cyg X-3 a black hole?

TL;DR

This study investigates the chaotic nature of accretion disks around neutron stars and black holes, analyzing observational data to distinguish between chaotic and stochastic behaviors, and suggests Cyg X-3 could be a black hole.

Contribution

It provides the first detailed nonlinear analysis of neutron star systems, comparing their dynamics with black holes, and proposes Cyg X-3 as a black hole candidate based on chaos analysis.

Findings

Sco X-1 and Cyg X-2 are low dimensional chaotic systems.

Cyg X-1 and Cyg X-3 are stochastic sources.

Cyg X-3 may be a black hole.

Abstract

The accretion disk around a compact object is a nonlinear general relativistic system involving magnetohydrodynamics. Naturally the question arises whether such a system is chaotic (deterministic) or stochastic (random) which might be related to the associated transport properties whose origin is still not confirmed. Earlier, the black hole system GRS 1915+105 was shown to be low dimensional chaos in certain temporal classes. However, so far such nonlinear phenomena have not been studied fairly well for neutron stars which are unique for their magnetosphere and kHz quasi-periodic oscillation (QPO). On the other hand, it was argued that the QPO is a result of nonlinear magnetohydrodynamic effects in accretion disks. If a neutron star exhibits chaotic signature, then what is the chaotic/correlation dimension? We analyze RXTE/PCA data of neutron stars Sco X-1 and Cyg X-2, along with the black hole Cyg X-1 and the unknown source Cyg X-3, and show that while Sco X-1 and Cyg X-2 are low dimensional chaotic systems, Cyg X-1 and Cyg X-3 are stochastic sources. Based on our analysis, we argue that Cyg X-3 may be a black hole.