Stars in many cases are just like people. Some big, some small and all levels between. Some have short lives living a maximum potential(Supernova)or live a more quieter life slowing fading away into the canvas of deep space. What does it mean to be a star other than some point of light in the night sky? First In order for a star to be born we have to start off with some very cold gas and dust. Over time this soup of gas and dust begins to collect together while growing heavier and heavier under gravitational circumstances. How gas and dust can collect to become star forming potential happens in many ways. Perhaps a fully formed interstellar beast sweeps by causing the gas to collapse in reaction. Or if any supernova happen in the area the traveling shock wave will cause gas to collapse.
Whenever any gas begins to collapse in on it self it generates heat. All a star needs is time and gas in order to be born. Depending what the final outcome will be when the gas ignites nuclear fusion is a different story. Just like water needing a 100 degrees to boil (Depending on altitude) a collapsing gas cloud needs tens of millions. When this barrier is reached stars ignite and come to life in the millions becoming part of the fascination to be gazed upon at night.
Although stars may start off in close associated clusters like schools of fish, as time goes by most drift apart into lonely parts of the cosmos. Even our sun was once part of a party but unfortunately for us this celebration ended quite some time ago. Somewhere out there the brothers and sisters of our sun live on possibly harvesting Earth-like planets and civilizations. If so, then maybe they are writing about our sun, a lost sibling like I am writing about theirs.
Stars can obviously out live any human. Fortunately for us as a civilization we have the opportunity to monitor many stars embedded within the night canvas. Just like you don't have to wait a lifetime for a person to perish or to witness an aged elder, you just have to keep an eye on the majority. Just like you may scan a local mall food court and spot all sorts of aged humans, one can scan a cluster of stars and see age difference among the many.
Just like a human carries with it certain attributes to being defined young, middle-aged or old so do stars. I wont go into great detail here because each stage of stellar evolution deserves its own essay. However much of a stars life cycle depends on mass. The bigger a star the faster it spends fuel during hydrogen nuclear fusion. Also the bigger the star the hotter it is. Therefor a large star is able to create many basic elements that we humans need for life (carbon, oxygen). The element that sends large mass stars to their early demise is iron. With every other element up to iron, energy is released when created. This is the opposite for iron for it actually consumes energy to fuse instead of releasing it. When enough iron accumulates in large mass stars they no longer can support them selves and they explode as supernova. However once this celestial event takes place it alone can outside galaxies. Due to enormous heat after a supernova further elements can be synthesized like gold for wedding bands. A great example of a supernova remnant is the Crab Nebula. A greater example of what a large mass star can become is a black hole. An example of which is Cygnus X-1 system.
What about lower mass stars like our own sun? Although much less timid than super giants nothing lasts forever. Classified as a yellow dwarf due to temperature. This status will change in around another 4.5 billion years when our sun inflates into a yellow giant. This happens because of lack of hydrogen for fuel so it burns the next best thing which is helium. This process inflates the sun to the point where it might even swallow all the orbits of the inner planets in the final outcome. Helium alone is not enough to sustain a star like our own though. As more time ticks away layers of an inflated star will shed much like a cricket shedding an exoskeleton. This process is better known as a planetary nebula and a great example to look at is the Cat's Eye Nebula.
We cant leave out stars with masses less than our sun Sol now can we? Of course not! These stars are classified as red dwarfs. These stars are very tiny and within our Milky Way galaxy they out number any other type of star. But not one can be seen with the naked eye. Red dwarfs are the coolest in temperature of the stellar zoo, blue giants being the hottest. If we were able to replace our sun with a red dwarf star we still wouldn't be able to see it unless much effort was being taken. For a planet like Earth to receive any decent amounts of solar energy it would have to be much closer than Mercury is to our sun now which is pretty close. Even with conditions like that I don't think you would get anything more than a dusk twilight on such a planet. Also out of all the stars, at least the ones I been discussing in this essay, the red dwarf lives the longest. Like I mentioned before nothing last forever. Red dwarf life span rivals the whole age of the universe!(14.5 billion years)so a red dwarf in the process of dying is not really expected as of yet so I cant tell you what exactly happens when one actually does die. Theory suggests red dwarfs simply fade away into black dwarfs (A chunk of coal-like material) in opposite comparison to blue giants who go out with a bang.
More exotic star breeds do exist such as neutron stars, brown dwarfs, pulsars and magnetars. All of which can be produced in the examples I stated above but deserve their own topic to be discussed in astronomical detail.