Currently, most scientists think that there are 4 types of black holes. Stellar mass. supermassive, intermediate and miniature. We understand little about each, some less than others but here is what we do know.

 

Stellar Mass Black Holes

 

Stellar mass black holes form when a star bigger than 3x the suns mass but smaller than 100 SM ( solar masses ) runs out of fuel to burn and collapses in on itself and forms a black hole. But there are other ways to form a stellar mass black hole, 1 is to merge a neutron star with another neutron star or a white dwarf  or when a neutron star accumulates more mass until it can overcome neutron degeneracy pressure. These last 2 ways can only happen in a binary system, where 2 stars are orbiting each other and where one star can suck material from another.

 

Supermassive Black Holes

 

In the middle of every galaxy so far observed, we have found a supermassive black hole and now scientists around the world think that they are crucial to the formation of Galaxies. These ginormous black holes can reach up to millions even billion times the mass of the sun ( solar masses ). The supermassive black hole at the centre of our galaxy is 4.3 million solar masses !! Unfortunately we still don't know how Supermassive black holes formed of how they got so big, but Scientist are still on the case and hopefully we swill find out soon .

 

 

Intermediate Black Holes

 

There is indirect evidence pointing towards these black holes that seems promising but some still doubt the existence of these black holes. Theoretically intermediate black hole have a mass in between 10-100 and 1 million - 1 billion solar masses, which is in between the masses of Stellar and supermassive black Holes. there are many candidates to be Intermediate BH but until we have further evidence, none can be classified by this name.

 

Miniature Black Holes

 

Unlike the other types of BH, these are purely theoretical, there is no evidence for them yet. In theory, miniature black holes have an event horizon at small as an atomic particle and were formed a few million years after the Big Bang. Many people have different theories about MBH, ranging from the idea that 'Miniature black holes are the doors to other dimensions' to 'we are all made up of mini black holes'. But, there is no evidence for black holes of stellar mass ( mass of the sun ) or less that were not produced by stellar collapse.

When I first learned about mini black holes, my first question was why they haven't grown bigger, I mean if they had been around since a few million years after the big bang, they would have a lot of time to absorb matter ad energy. So I asked this question on Quora and 3 people were kind enough to answer. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What I have understood from this is that, since mini black holes are so small, and the universe is so big ( and getting bigger ) there is a lot of space that is needed to be covered in order to find matter to be absorbed.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This one is pretty self expalintory

 

 

 

 

 

 

 

 

 

 

 

 

Same for this one.

 

Here is a video recap of what I have talked about