It is estimated that the stars with 20 times the Sun’s mass may end up with the birth of the Stellar Black Holes. The mass of these Black Holes are estimated to be more than 100 times the mass of our Sun. These stars can gain more mass by the collisions with other stars and Black Holes. The Stellar mass Black Holes which are found so far are paired with stars which made it a little bit easy to figure them out. In some cases called X-ray Binaries , the black pulls of the gas from the star which gets into its accretion disk and gets heated up, resulting in the emission of X-rays. Nearly 50 Stellar mass Black Holes are revealed by these circumstances in our galaxy. But scientists suspect nearly 100 million of these Black Holes just in our Milky Way. 

Supermassives can be found in the centres of every galaxy and we do have one in our Milky way called Sagittarius-A. These blacks have their masses ranging from tens of thousands to billions of times the mass of our Sun. Our Sagittarius-A have a mass of 4 million times the mass of our Sun. This number might look so big but comparatively is it smaller than other Black Holes found in other galaxies like TON -618 which is being the largest Black Hole with 40 billion times the mass of our sun. The birth of these Black holes still remains unknown and this makes it one of the interesting topics to search about Black Holes. It is estimated that these supermassive Black Holes would have formed after one billion years after the Big Bang. These Black Holes might have been formed by the supernova of the supermassive stars in the early universe , which might have been the starting point of these supermassive monsters.  These supermassive monsters may grow even bigger by feeding on other stellar mass matters and neutron stars. These Black Holes can merge to one another during the collision of 2 galaxies. 

These Black Holes still puzzle the minds of scientists with their no continual masses between these Black Holes and stellar and supermassive black holes. Scientists think that these are the results of the collision of 2 stellar mass Black Holes, where it keeps a check mate point - question… But still it is estimated that these Black Holes may have their masses around one hundred to hundreds of thousands of times the Sun’s mass or tens of thousands. Many of these Black Holes are identified but not yet confirmed because of the puzzling questions they leave behind. 

These are theoretically said by the scientists but we have no proven evidence to show their existence. It is being estimated that these Black Holes might have formed in the very first second of the birth of our Universe. The mass of these Black Holes might range from 10^(-8) to more than ten thousand times the mass of our Sun. Scientists say that these Black Holes would have evaporated eventually in the course of time as theoretically, less massive Black Holes will evaporate more quickly than the massive ones. But still scientists do have hope on the ones which have more mass of these black holes, which could still survive in this Universe somewhere, far away.