# destruction of gravitationally bound systems

16 Jan 2013Is it possible that gravitationally bound systems (clusters, galaxies, globular clusters, solar systems, planets with moons) are taken apart by the Hubble-expansion? If yes, under which circumstances and on what time scale?

bonus question: can you show that the integral over spherical harmonics almost always vanishes, \(\int\mathrm{d}\Omega\:Y_{\ell m}(\theta,\phi) = 0\) except of course for the monopole \(\ell = m =0\)?