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 5×10 42 erg s −1 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 1.3 × 10 43 erg s −1 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.