magnetic field effects in the initial collapse of polytropic clouds

In this paper, we investigate the in uence of the magnetic eld and the temperature gradients on the stability of a spherical cloud. observational data conrm a power-law relation between the magnetic eld and the gas density. here, we study the stability of a magnetized cloud with a toroidal magnetic eld and the polytropic equation of state. we nd that density and mass proles of the modied clouds are departed from the non-magnetized isothermal case. as the result, the critical mass, radius and density contrast at the onset of the gravitational instability dier from the critical bonnor-ebert mass and its critical radius and density contrast. thus, both the magnetic eld and the temperature gradients play important roles in the structure of the cloud. furthermore, the cloud critical mass is increased for the higher values of the polytropic exponent, irrespective of the values of the magnetic to thermal pressure ratios or the eld gradients. dierent values of the magnetic eld gradient and strength change the values of the critical density contrast and radius of the cloud; however, both of them fade their importance in the values of the critical mass.