Optoelectronic Memory Interface

Accreting neutron stars and black holes: a decade of discoveries

“…Current models of the variable-frequency QPOs require the presence of a characteristic radius, across which the properties of the accretion disks change considerably. The observed QPO frequencies are then attributed to the characteristic dynamic or hydrodynamic frequencies of the accretion flow at that radius (e.g., Stella, Vietri & Morsink 1999;Titarchuk et al 1999;Psaltis & Norman 1999) or, in the case of neutron stars, to the coupling of these frequencies to the stellar spin (Miller, Lamb & Psaltis 1998). On the other hand, models of the constant-frequency QPOs in black-hole systems are based on the trapping of oscillatory modes in accretion disks caused by the properties of the relativistic spacetime (Wagoner 1999;Kato 2001) or on the non-linear coupling of different frequencies near the black-hole event horizons (Abramowicz & Kluzniak 2001).…”