Only a supermassive black hole could account for that much energy in that small a space. HST has resolved quasar host galaxies, showing that many quasars live at the hearts of massive galaxies that have undergone collisions. Most stars in the galaxy are dwarf stars, including the Sun. HST has made measurements of red dwarf stars, which are only a fraction of the mass and radius of our Sun, and found evidence for surface magnetic fields stronger than expected. New theories of stellar interiors for low mass stars have to be made in order to explain these HST observations.
Giants burn the fuel in their stellar cores faster than dwarfs.
In fact, the bigger the star, the faster it is burning up, and therefore the shorter its lifetime. And giant stars end their normal lives with a spectacular supernova explosion. Giants have a great effect on their neighborhoods since they are constantly transferring material from their surfaces to the space around them. And our theories of stellar evolution of massive stars are based upon the careful observations of these objects. HST has made many important observations of giant stars, most notably in our satellite galaxies, the Large and Small Magellanic Clouds, where the incredible resolution of HST allows us to see individual giant stars in regions that look like bright blobs from ground-based observations.