Astronomers do indeed propose the existence of different types or classes of supermassive black holes in the universe. While our understanding is still evolving, there are a few proposed distinctions between these black holes based on their characteristics and properties. Here are a few examples:
Classical Supermassive Black Holes: These are the most commonly known type of supermassive black holes, which are believed to reside at the centers of most galaxies, including our own Milky Way. They are characterized by their enormous masses, ranging from millions to billions of times the mass of the Sun. Classical supermassive black holes are thought to form through processes such as the accretion of matter, mergers of smaller black holes, or direct collapse of massive gas clouds in the early universe.
Intermediate-Mass Black Holes (IMBHs): Intermediate-mass black holes have masses ranging from hundreds to thousands of times that of the Sun. They are smaller than classical supermassive black holes but larger than stellar-mass black holes, which form from the collapse of massive stars. The existence of IMBHs is still a topic of active research and observation, but they are thought to potentially form through various mechanisms, such as the runaway merging of smaller black holes or the direct collapse of massive stars.
Ultramassive Black Holes: Ultramassive black holes, as the name suggests, would be exceptionally large, with masses reaching tens or hundreds of billions of solar masses. These hypothetical black holes would represent an extreme end of the supermassive black hole spectrum. The formation mechanisms and observational evidence for ultramassive black holes are still under investigation, and no confirmed detection has been made thus far.
It is important to note that our knowledge of black holes, particularly supermassive black holes, is continually advancing. Further observations, theoretical developments, and studies, including the use of gravitational wave detectors and astronomical surveys, are likely to provide new insights into the nature and classification of black holes in the future.