File:Artist's Concept Illustrating Bulge & No Bulge Spiral Galaxies.jpg

English: This artist's concept illustrates the two types of spiral galaxies that populate our universe: those with plump middles, or central bulges (upper left), and those lacking the bulge (foreground). New observations from NASA's Spitzer Space Telescope provide strong evidence that the slender, bulge-less galaxies can, like their chubbier counterparts, harbour super-massive black holes at their cores. Previously, astronomers thought that a galaxy without a bulge could not have a super-massive black hole. In this illustration, jets shooting away from the black holes are depicted as thin streams. The findings are reshaping theories of galaxy formation, suggesting that a galaxy's "waistline" does not determine whether it will be home to a big black hole.