Sound waves in the intracluster medium of the Centaurus cluster
  We report the discovery of ripple-like X-ray surface brightness oscillations in the core of the Centaurus cluster of galaxies, found with 200 ks of Chandra observations. The features are between 3 to 5 per cent variations in surface brightness with a wavelength of around 9 kpc. If, as has been conjectured for the Perseus cluster, these are sound waves generated by the repetitive inflation of central radio bubbles, they represent around 5x10^42 erg/s of spherical sound-wave power at a radius of 30 kpc. The period of the waves would be 10^7 yr. If their power is dissipated in the core of the cluster, it would balance much of the radiative cooling by X-ray emission, which is around 1.3x10^43 erg/s within the inner 30 kpc. The power of the sound waves would be a factor of four smaller that the heating power of the central radio bubbles, which means that energy is converted into sound waves efficiently. 
J.S Sanders, A.C. Fabian (Institute of Astronomy, Cambridge)