If you want to find out what pulsars are, please click here . The other kind of nebulae are called diffuse nebulae. Diffuse nebulae usually have more gases and dust in them than the planetary nebulae do. These diffuse nebulae can be light-years long and have no definite shape. An example of a diffuse nebulae is the Great Nebula in the Orion constellation.
Stars form by gases and dust clumping together.
This is because all matter contains gravity, and when the clumps of gas and dust get together, the pressure creates heat and the pockets of gas and dust turn into a protostar. This process takes a few millions of years, only a very small portion of a star's life. Sometimes if protostars spin very quickly, it may split into two protostars. This forms a binary star system. Scientists can tell whether or not there is a black hole in a binary star system because of how the black hole affects the other star.