  Sharp fronts observed by Chandra satellite between dense cool cluster cores
moving with near-sonic velocity through the hotter intergalactic gas, require
strong suppression of thermal conductivity across the boundary. This may be due
to magnetic fields tangential to the contact surface separating two plasma
components. We point out that a super-Alfvenic motion of a plasma cloud (a core
of a merging galaxy) through a weakly magnetized intercluster medium leads to
"magnetic draping", formation of a thin, strongly magnetized boundary layer
with a tangential magnetic field. For supersonic cloud motion, M_s > 1,
magnetic field inside the layer reaches near-equipartition values with thermal
pressure. Typical thickness of the layer is L /M_A^2 << L, where L is the size
of the obstacle (plasma cloud) moving with Alfven Mach number M_A >> 1. To a
various degree, magnetic draping occurs both for sub- and supersonic flows,
random and ordered magnetic fields and it does not require plasma
compressibility. The strongly magnetized layer will thermally isolate the two
media and may contribute to the Kelvin-Helmholtz stability of the interface.
Similar effects occur for radio bubbles, quasi-spherical expanding cavities
blown up by AGN jets; in this case the thickness of the external magnetized
layer is smaller, L /M_A^3 << L.
