Types of black holes. These black holes are also referred to as collapsars
Most stellar black holes, however, lead isolated lives and are impossible to detect. Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that comes from the collapse of a massive star.
The supermassive black hole at the center of the Milky Way, Sagittarius A*, is 4.3 million solar masses. These "stellar" black holes are generally around 10 solar masses.
So far, the LIGO and Virgo gravitational-wave detectors have teamed up to uncover 20 stellar-mass black holes in the process of merging to form black holes ranging from about 20 to 80 solar masses. As mass gets added, the neutron star gets smaller, just as we also found for white dwarfs!
The black holes we know about tend to fit into two size categories: "stellar" size are around the mass of one star while "supermassive" are the mass of several millions of stars. Normal black-holes, or ‘Stellar Mass Black Holes’, form from the collapse of massive stars as their life comes to an end.
Judging from the number of stars large enough to produce such black holes, however, scientists estimate that there are as many as ten million to a billion such black holes in the Milky Way alone. Traditionally, astronomers have talked about two basic classes of black hole – those with masses about 5-20 times that of the sun, which are called stellar-mass black holes, and those with masses millions to billions times that of the sun, which are called supermassive black holes. "We weren't expecting to find a stellar-mass black hole this massive," said study team member Andrea Prestwich of …
The big ones are located at the centers of large galaxies. A stellar black hole (or stellar-mass black hole) is a black hole formed by the gravitational collapse of a star. They have masses ranging from about 5 to several tens of solar masses. A supermassive black hole, as you suggested, just has more mass; It has a lot more mass than a stellar mass black hole. The black hole pulls material from a massive, blue companion star toward it.
While it may seem as though a stellar black hole would be the largest black holes, there is observational proof that other types of black holes exist that are much larger than a stellar mass black hole. As stars reach the ends of their lives, most will inflate, lose mass, and then cool to form white dwarfs . Stellar remnants larger than ~ 5M face yet another fate -- a black hole..
The mass-size relationship for neutron stars is shown by the blue line.
Stellar-mass black holes are typically in the range of 10 to 100 solar masses, while the supermassive black holes at the centers of galaxies can be millions or billions of solar masses.
Some where between 3 and 5 M there is a limit on the sizes of neutron stars analogous to the 1.4M limit to white dwarfs.
However, the collapse of larger stars is much more intense, and this collapse actually results in a black hole. The process is observed as a hypernova explosion or as a gamma ray burst. The most commonly known way a black hole forms is by stellar death. Every galaxy is full of them, scattered from top-to-bottom.