A shared accretion instability for black holes and neutron stars

Accretion disks around compact objects are expected to enter an unstable phase at high luminosity(1). One instability may occur when the radiation pressure generated by accretion modifies the disk viscosity, resulting in the cyclic depletion and refilling of the inner disk on short timescales(2). Such a scenario, however, has only been quantitatively verified for a single stellar-mass black hole(3-5). Although there are hints of these cycles in a few isolated cases(6-10), their apparent absence in the variable emission of most bright accreting neutron stars and black holes has been a continuing puzzle(11). Here we report the presence of the same multiwavelength instability around an accreting neutron star. Moreover, we show that the variability across the electromagnetic spectrum & mdash;from radio to X-ray & mdash;of both black holes and neutron stars at high accretion rates can be explained consistently if the accretion disks are unstable, producing relativistic ejections during transitions that deplete or refill the inner disk. Such a new association allows us to identify the main physical components responsible for the fast multiwavelength variability of highly accreting compact objects.

Automated summary

Accretion disks around compact objects may become unstable at high luminosities. The radiation pressure generated by accretion can modify the disk viscosity, resulting in cyclic depletion and refilling of the inner disk on short timescales. This phenomenon has only been quantitatively verified for a single stellar-mass black hole, and its absence in most bright accreting neutron stars and black holes has been a puzzle. However, we have now observed the same multiwavelength instability around an accreting neutron star and found that the variability across the electromagnetic spectrum of both black holes and neutron stars can be explained consistently if the accretion disks are unstable.