Greetings, ceowang!
From Astronomer Michael L. Allen's website at Washington State
University:
Stars: Properties and Evolution
"Nearly everything you see around you was manufactured in stars. Stars
assemble hydrogen atoms into heavier atoms, a process called 'stellar
nucleosynthesis'...
Hydrogen was probably formed as a result of an asymmetry in a
particular creation-annihilation quantum fluctuation process during
the first minute or so of the lifetime of the universe."
Star Formation
"During cloud collapse, once the temperature gets high enough for
hydrogen to be fused into helium, we say that a star is born.
...four hydrogen nuclei collide to produce a single nucleus of
helium-4.
...This fusion reaction produces energy.
...The released energy becomes heat inside the star, which allows
further fusion reactions to occur."
"The hydrogen core-burning stage of a star's life is called the main
sequence stage. During the main sequence stage, helium will collect in
the stellar core over time. It is the changing chemical composition of
the star drives stellar evolution. The main sequence stage is by far
the longest stage of a star's life, occupying more than 90% of a
star's total lifetime."
"When about 10% of the hydrogen is burned, then hydrogen burning moves
to a shell outside the core. The star's atmosphere expands and cools
and the star becomes a red giant..."
http://astro.wsu.edu/allen/courses/astr135/Notes/stars.html
From the SciDAC Center for Supernova Research:
"Supernovae are broadly classified by two types based on the presence
(Type 2) or absence (Type 1) of hydrogen in their light spectrum.
Although both types release similar amounts of energy in optical
light, they are totally different astrophysical systems.
A Type 2 supernova is the end result of the evolution of a massive
star. All stars spend most of their lives 'burning' hydrogen to make
helium, and releasing energy as a byproduct. The energy liberated
during nuclear burning provides the star with pressure support against
the force of gravity, which would otherwise cause it to collapse."
http://www.pnl.gov/energyscience/01-02/art3.htm
How does this Hydrogen-burning process relate to our sun?
From Cornell University Professor James Bell's Astronomy 102/104: Our
Solar System Lecture 35, "The Sun" (April 24, 2002):
"The Sun's Interior Engine
* Collapse of the solar nebula --> central concentration of H, He
* As central pressure increased, central temperature increased...
* Central pressure and temperature became so great that Hydrogen atoms
could be converted to Helium atoms by nuclear fusion reactions:
4 H[ydrogen] --> He[lium] + Energy
* Hydrogen is being "burned" into Helium deep inside the Sun's core!
* How fast is the Hydrogen "fuel" being burned up?
- The luminosity of the Sun implies 700,000,000 tons of Hydrogen
per second
* Wow... So when will the fuel run out?
- The Sun has been burning Hydrogen for ~ 4.6 billion years
- At 700,000,000 tons per sec, the Sun has converted ~ 4% of its
mass from H --> He
- This is thought to be about 50% of the mass of H in the Sun's
core
- So the Sun is roughly a "middle aged" star, with another ~5
b[illion] y[ears] of life expectancy."
http://astrosun.tn.cornell.edu/courses/a102/lectures/Lecture35_4.pdf
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