Stellar Evolution
If we want to know about ASTRObiology, we had better know something about the stars.
Firstly, when we talk about stellar evolution, we use the word evolution to mean 'change over time'. Don't get confused between the biological Theory of Evolution and stellar 'evolution' as used by astronomers. These are completely different processes - remember, stars aren't alive.
You probably know that stars are massive balls of condensed gas pulled together under immense pressure by gravity. One of the smallest known stars is only 16% bigger than Jupiter, however it is 96x as massive. Try to imagine the weight of 167,000km of gas and dust all wanting to be where you are (the atmosphere on Earth is only around 100km thick)! Pressures are so high at the cores of stars that atoms are squashed together to form heavier stable elements in a process called fusion. On a side note, you can think of fusion as essentially the opposite of fission, or spliting of the atom, which is the process used to make a the first nuclear bombs (hydrogen bombs fusion devices). Both fusion and fission release energy, however fusion involving elements heavier than iron (Fe) will absorb energy. This fact about fusion is why a sufficiently massive star with an iron core is at the end of its life; it's game over. No more energy is being produced, and the star goes supernova.
It is believed that if fusion can be controlled and scaled down to safe, workable sizes, we could solve much of the energy crisis currently contributing to climate change. A 'large' scale fusion reactor is currently being designed and built in France. In Australia, we too have a Plasma Fusion Research Facility.
To understand how stars generate so much energy, the different types of stars and how one type of star can become another type over time, it is important to take a moment now to make sure you understand the most famous equation in physics, E=m/c2 - do your best to understand what is being said in the video below - it'll blow your mind!
Massive Stars
All of the properties of a star (luminosity, temperature, size, density, etc.) are explainable by how massive a star is. This is important in astrobiology because the mass of a star determines its type, which in turn defines how far away from the star a planet needs to be orbiting so that it is in what we call the habitable zone. (This is explained on the exoplanets page of this site.)
Right, so now that we understand basically what a star is and what gives a star its energy, let's look at the Life Cycle of Stars...
The most astounding fact
You may have heard it said that the stars died so that we may live. While we often talk of stars being born and dying, stars are not alive as you know (we'll get to what life is soon enough). Everything around you, EVERYTHING (including you) has been formed from atoms that were cooked in the inner depths of stars. Think about that just for a moment: EVERYTHING was once part of a star. These stars died long ago, leaving behind vast nebulous clouds out of which new stars and planets and all of life grow. If you haven't heard Neil de Grasse Tyson's most astounding fact, here he is:
Let's keep exploring...
