Gravitational waves from collapsing globular cluster systems
  The evolution of globular cluster systems in some galaxies can be cause of merging of globulars in the very central regions.   This high stellar density favours the growth of a central nucleus via swallowing of surrounding stars. The infall of stars into a nuclear black hole is here shown to be, under certain conditions, not only source of electromagnetic radiation but also a significant source of gravitational waves. 
Roberto Capuzzo-Dolcetta (1), Paolo Miocchi (2) ((1) Inst. of   Astronomy, Universita' di Roma La Sapienza, (2) Dept. of Phy...