  We present preliminary results of the XMM-Newton 50 ksec observation of the
Perseus cluster. The global east/west asymmetry of the gas temperature and
surface brightness distributions, approximately aligned with the chain of
bright galaxies, suggests an ongoing merger, although the modest degree of the
observed asymmetry certainly excludes a major merger interpretation. The chain
of galaxies probably traces the filament along which accretion has started some
time ago and is continuing at the present time. A cold and dense (low entropy)
cluster core like Perseus is probably well "protected" against the penetration
of the gas of infalling groups and poor clusters whereas in non-cooling core
clusters like Coma and A1367, infalling subclusters can penetrate deeply into
the core region. In Perseus, gas associated with infalling groups may be
stripped completely at the outskirts of the main cluster and only compression
waves (shocks) may reach the central regions. We argue that the passage of such
a wave(s) can qualitatively explain the overall horseshoe shaped appearance of
the gas temperature map (the hot horseshoe surrounds the colder, low entropy
core) as well as other features of the Perseus cluster core. As compression
waves traverse the cluster core, they can induce oscillatory motion of the
cluster gas which can generate multiple sharp "edges", on opposite sides or the
central galaxy. Gas motions induced by mergers may be a natural way to explain
the high frequency of "edges" seen in clusters with cooling cores.
