  We present a linear analysis of the radiative Rayleigh-Taylor (RT)
instability in the presence of magnetic field for both optically thin and thick
regimes. When the flow is optically thin, magnetic field not only stabilizes
perturbations with short wavelengths, but also growth rate of the instability
at long wavelengths is reduced compared to a nonmagnetized case. Then, we
extend our analysis to the optically thick flows with a conserved total
specific entropy and properties of the unstable perturbations are investigated
in detail. Growth rate of the instability at short wavelengths is suppressed
due to the presence of the magnetic field, however, growth rate is nearly
constant at long wavelengths because of the radiation field. Since the
radiative bubbles around massive protostars are subject to the RT instability,
we also explore implications of our results in this context. In the
nonmagnetized case, the growth time-scale of the instability for a typical
bubble is found less than one thousand years which is very short compared to
the typical star formation time-scale. Magnetic field with a reasonable
strength significantly increases the growth time-scale to more than hundreds of
thousands years. The instability, furthermore, is more efficient at large
wavelengths, whereas in the non-magnetized case, growth rate at short
wavelengths is more significant.
