Alireza Khesali

In this paper, the stability of radiation–pressure-dominated accretion discs in the presence of magnetic field and the time delay between the stress and the pressure were investigated. The response of magnetic field to perturbation of height was considered as Bϕ1/Bϕ = −mH1/H. According to Ciesielski et al. (2012), for the delay larger than a critical value (e.g. if omegaτ <−125 for α = 0.1, β = 0 and ξ = 1), two real solutions would exist, both negative, and thus the system tended to be stable. However, this time delay would be much longer than the time delay shown by the simulation work (10 − 20 omega), not capable of answering the stability problem of radiation-pressure accretion discs. In this paper, the problem has been reviewed in the presence of a magnetic field again. Results showed that the presence of a magnetic field would decrease critical values of time delay to make the system stable. The results could also improve if radiation-pressure-dominated discs were stable at the critical value omegaτ < −35 when α = 0.1, β = 0, ξ = 1, m = 3 and βm = 0.01. This critical value was much closer to the obtained value from time delay by the simulation work. The magnetic field could stabilize radiation-pressure-dominated discs. However, if magnetic pressure dominated in the system, the stability of the system would decrease again.