Often when we look into the night sky we don't think of the stars, celestial bodies of dynamic energy shining for many millions of years as having a lifespan. Stars start out in stellar nurseries. If you've ever seen a picture of the Eagle Nebulae and most likely you have at some point, you are looking at a stellar nursery. The Pillars of Creation which are two beautiful and impressive columns within the Eagle Nebulae are one of many star forming regions in the universe. Within these nurseries stars are created in clouds of gas and dust and heavier elements like iron. One of the most important elements in a star is hydrogen. Stars are also made of helium and vast quantities of iron. All this these elements and matter creates mass. Gravity, the most important force in the universe, is needed to pull the mass of a forming star together so that it may ignite and begin burning. After being brought together by gravity to form a cohesive mass it begins to spin faster and faster until it heats up. When it heats up to a certain point nuclear fusion happens! This nuclear reaction gives the star its energy and heat.
But stars have a major problem. Just as gravity is necessary in order for the materials to form a star, gravity is also what will eventually destroy it. Gravity is relentless. Some objects begin the star formation process but never quite make it because they don't have enough of the right elements or enough power to create a nuclear reaction to hold together against gravity. The planet Jupiter is most likely one of those objects: a failed star. These are called brown dwarfs. Brown dwarfs. They emit little light or heat and so they cannot power themselves. Stars need a powerful force to hold up against gravity and prevent collapse. Nuclear fusion creates enough pressure to stand up against gravity.
The color of a star lets you know how hot it is and how old it is. There are young, blue large main sequence stars, middle aged stars like our sun and older small red stars. Older still are white dwarfs. Bigger, more massive stars live shorter lives than lower mass stars because they burn out much faster. A high mass star may only live a few million years while a low mass star can live for billions of years.
Even with all of its massive power and energy a star cannot last forever against the relentless force of gravity. There are layers that a star burns through before it collapses. First it burns through it's hydrogen layer. Once that happens it begins to burn its supply of helium and so on until it gets to its iron core and has nothing left to burn. At this point it gets so hot that it ejects its remnant of gases and matter and creates a planetary nebulae. At this point it may begin to look like a red giant. But it's core is very small at this stage and is on the verge of collapse. But many stars go through different stages of aging before this happens and some stars have a very different end than others. Let's examine this last stage:
With some stars, when gravity begins to take over they find escape in the electrons within the core. The electrons create what is called electron degenerative pressure and gravity can't further compress it any longer because the electrons won't allow it. So such a star at this stage cools off and it becomes a white dwarf. White dwarfs that aren't loners become Type 1 A Super Novas at death. Type 2 Super Novas are the deaths of more massive stars.
Even after this stage gravity has a way of getting beyond the force of electron degenerative pressure in the core of a white dwarf. What can happen at this stage in some stars is that gravity may turn the electrons into neutrons. Neutrons don't like pressure either and react similarly. So then the white dwarf becomes an even smaller, neutron star. One teaspoon of neutron star material weighs 1billion tons! Neutron stars spin much faster than other stars and they become like stellar lighthouse beams - what scientists call pulsars!
This is what generally happens to lower mass, medium-sized stars and small stars. A very massive star's collapse will result in a black hole. A black hole is created when a star is so powerful that in its death gravity causes it not to explode but to it close in on itself. Black holes are the mysterious, powerful gravity wells in the universe from which nothing can escape, not even light! They are massive "holes" in space, the most massive things in the universe. They can be found near stars, slowly consuming them, they can rove around in space alone and they can be found at the vortex of galaxies. A rare occurrence with the death of massive stars is the phenomenon of the mega-explosive. A star can be so massive that when it collapses they leave nothing behind! They don't even become black holes! Stars like this, right before they disappear forever, become mega-explosives or mega-super novas.
These kinds of massive stars - mega explosives, are the sort of stars that many scientists think seeded the universe with all of the stars and galaxies we see today. When stars explode they produce tremendous amounts of iron which in turn feeds new stars. Scientists believe that the key to understanding how the universe formed is within these mega-explosive stars. Thus the life and death of stars.