Stars are formed in clouds of gas and dust, known as nebulae. Nuclear reactions at the center (or core) of stars provides enough energy to make them shine brightly for many years. The exact lifetime of a star depends very much on its size. Very large, massive stars burn their fuel much faster than smaller stars and may only last a few hundred thousand years. Smaller stars, however, will last for several billion years, because they burn their fuel much more slowly.
To the Sun, it would take a collection of gas and dust a hundred times the size of our Solar system. This is just the beginning.Once such a large amount of gas and dust huddle together, they form what we call a protostar. An object is considered a protostar for as long as material is still falling inward. For our Sun, and stars of the same mass, the protostar phase would have ended after approximately 100,000 years. After this, the protostar stops growing and the disk of material surrounding it is destroyed by radiation.
If the protostar was unsuccessful in acquiring enough mass, a brown dwarf will come into shape. a brown dwarf is too big to be called a planet, and too small to be called a star.
The main sequence phase
If the star is big enough to fuse hydrogen atoms into helium, it will enter the phase that our Sun is in, called the main sequence phase.
After the main sequence phase, the star will become a red giant. A red giant is a dying star in one of the last stages of stellar evolution. In a few billion years’ time, our Sun will die and expand, gobbling up the inner planets. The energy of the star will spread out across a larger area, Because of this, the star actually becomes cooler reaching only a little more than half the heat of the Sun. The temperature change causes stars to shine more towards the red part of the spectrum; it is this that gives a red giant its name.
From this point Smaller stars, up to around 8 times the mass of our sun, can become a white dwarf. These old stellar remnants are incredibly dense. A teaspoon of their matter would weigh as much on Earth as an elephant – that’s 5.5 tons in one incredibly strong teaspoon.
A white dwarf’s radius is just .01 times that of our Sun, but the mass is about the same. Estimating how long a white dwarf has been cooling helps astronomers increase their understanding of how old the universe really is.
After an unimaginable amount of time– tens or even hundreds of billions of years – a white dwarf will cool until it becomes a black dwarf, which are invisible because they are emitting at the same temperature as the microwave background. Because of the age of the universe and what we know about its oldest stars, there are no known black dwarfs.
Alternatively, a star with at least eight solar masses will have a much more violent, yet much more beautiful, death. Massive stars can create a supernova when they run out of fuel.
Black Holes / Neutron stars
After the supernova explosion, the star’s core is left behind in the form of either a black hole or a neutron star, both of which are incredibly destructive and violently beautiful.