Black holes are some of the most mysterious and extraordinary objects in the universe. These cosmic entities are created when a star collapses in on itself, forming a point of infinite density and gravitational pull.

Black holes come in a variety of sizes, with the smallest being primordial black holes. These black holes, which may or may not exist, would be much smaller than a proton if they did exist. Stellar black holes, on the other hand, are formed when a star collapses and typically have a few times the mass of our sun. The largest known stellar black hole is M33 X-7, which has a mass of 15.65 solar masses and is 92 km wide.

There is a gap in the sizes of known black holes between those that are around 150 solar masses and those that are millions of times more massive. This may be due to the time it takes for black holes to merge and grow to these larger sizes. The largest known black hole is located in the center of the galaxy NGC 4889 and has a mass of 21 billion solar masses, which is over 250 million times more massive than the black hole at the center of the Milky Way.

In addition to size, black holes are also classified based on their properties. The three main types of black holes are: stellar black holes, intermediate-mass black holes, and supermassive black holes. Stellar black holes are the most common and have masses ranging from a few solar masses to a few tens of solar masses. Intermediate-mass black holes are larger than stellar black holes and have masses ranging from a few hundred to a few tens of thousands of solar masses. They are thought to be formed through the merging of smaller black holes or by the collapse of very massive stars. Supermassive black holes are the largest known black holes and can have masses millions or billions of times that of the sun. They are found at the center of most galaxies, including our own Milky Way.

There is also the theoretical possibility of microscopic black holes, which would be even smaller than primordial black holes and could potentially be created in high-energy particle collisions. However, these have not yet been observed and their existence is still a topic of debate among scientists. Despite their size and gravitational pull, black holes remain some of the most enigmatic objects in the universe and there is still much that we don’t understand about them.