75% Hydrogen, 24% Helium, 1% everything else.
The Main Sequence Stage:
T Core 10 x 10 K =
Hydrogen fusion nuclear reactions in the core.
A star spends its life in a delicate balance between outward radiation pressure and inward
~90% ~95% of stars are Main Sequence…
Including our sun.
Hydrogen Fusion Reactions= Proton-Proton Chain:
1 1 2 +
H + H = H + e + V(deuterium, position, neutrino).
2H = H= He + V (helium, istotope, radiation burst).
3 3 4 1 1
He = He = He + H + H (helium, hydrogen).
*NOTE: FILL IN THE MISSING BLANKS FOR THE ABOVE EQUATIONS ON
TEST # 2!
Strong force – nuclear force – 2 particles with in 1015m together. Dominant nuclear
reactions that take place in 90-95% stars
Note that four Hydrogen nuclei fuse to form one Helium nucleus and …
A small amount of mass is released as energy.
(4.3 x 10 -12J).
Not much energy produced…
But…a typical star has 10 such reactions each second!
Therefore, the energy produced each second is
(4.3 x 10 J) (1 x 10 ) = ~ 4 x10 w.6
This is the Luminosity (energy per second) observed for our sun (a typical star).
Luminosity = L = 4 (3.14) R (SIGMA SIGN) T = energy/s.
Life on the Main Sequence:
A “Main Sequence” star fuses Hydrogen nuclei into Helium nuclei deep in its core via p-
p chain(=proton-proton chain). 6
Core temperature must be at least 10 x 10 K = 10 million K. REMEMBER THIS FOR
4 H = 1He
~10 38 such reactions occur each second.
Massive stars: greater core densities and greater core pressures.
Faster rate of Hydrogen fusion=
Shorter Main Sequence lifetime of only a few Million years.
Average, normal stars (like our sun) will fuse Hydrogen over lifetime of several billion
90% - 95% of stars are Main Sequence stars. ASK THIS ON TEST The Sun:
Massive stars only live for a few million years.
Normal stars live for billions of years.
Our Sun, a normal star, will fuse Hydrogen in its core for a total of ~10 billion years.
Our sun is now 4.5 billion years old.
~55% of stars have a companion.
*NOTE: ON TESTS # 2 QUESTION: WHAT IS ANOTHER NAME FOR
Mass extinctions occur on Earth ~every 25=30 million years.
Perhaps the sun has a never-observed companion which comes near to the sun
It disturbs the orbits of nearby comets, asteroids, meteors.
These may crash into Earth and precipitate mass extinctions.
Characteristics of Nemesis:
If it exists.
Mass ~0.01 M o.
Distance ~ 89 x 10 AU ~ 90,000 Astronomical Unit.
WHAT DOES NEMESIS MEAN? SOMETHING THAT CAUSES MISERY,
PAYBACK. IN CASE: ON TEST
Period ~26 million = 30 million years.
The Red Gi