What are the main differences between stellar black holes and super massive black holes?
Supermassive black holes have properties which distinguish them from lower-mass classifications: * The average density of a supermassive black hole (defined as the mass of the black hole divided by the volume within its Schwarzschild radius) can be very low, and may actually be lower than the density of air. This is because the Schwarzschild radius is directly proportional to mass, while density is inversely proportional to the volume. Since the volume of a spherical object (such as the event horizon of a non-rotating black hole) is directly proportional to the cube of the radius, and mass merely increases linearly, the volume increases by a much greater factor than the mass as a black hole grows. Thus, average density decreases for increasingly larger radii of black holes (due to volume increasing much faster than mass). * The tidal forces in the vicinity of the event horizon are significantly weaker. Since the central singularity is so far away from the horizon, a hypothetical astron
