Gravity can result in very efficient energy release! We have already encountered gravitational energy release in the youngest and oldest stars (the first, in the energy radiated before the star reaches the main sequence, the second in the collapse to a white dwarf, neutron star, or black hole and subsequent activity). However, gravitational energy plays a much more dramatic role around the supermassive black holes -- up to a trillion sun masses or so -- that lie in the very centers of galaxies. Matter falling into these black holes produces active galactic nuclei (AGNs), emitting as much energy as the entire remaining galaxy in which they live. AGNs emit brightly across the whole electromagnetic spectrum, from radio through X-rays and often gamma rays, and they show dramatic effects such as narrow "jets" where material is being ejected at nearly the speed of light.