Final answer:
Giant black holes with masses millions to billions of times that of our Sun, located at the centers of galaxies, are called supermassive black holes. They are associated with phenomena like quasars in young galaxies and play a crucial role in galactic dynamics.
Step-by-step explanation:
The name given to the giant black holes thought to reside in the centers of many galaxies and to power active galactic nuclei is supermassive black holes. These enormous cosmic entities can have masses millions to billions of times that of our Sun and are critical to the dynamics and evolution of galaxies. Observations by instruments like the Hubble Space Telescope have provided evidence for their existence, revealing features like rapid rotation of accretion disks and jets of material being ejected from the centers of galaxies.
Among the different phenomena associated with such supermassive black holes, quasars represent young galaxies that have active and energetic cores due to a forming supermassive black hole. Over time, quasars become less energetic as the black hole consumes surrounding matter and quiesces. Moreover, these black holes influence their host galaxies by shaping stellar evolution and providing a mechanism for the emission of high-energy radiation.