gravity tries to pull 1/4 pounder to center of the Earth
pressure from table opposes gravity
hydrostatic equilibrium on Sun
"cloud of gas" (like 1/4 pounder)
gravity pulls cloud to the center
pressure from gas below opposes gravity
heat from fusion in the hot core increases pressure
energy output controls size of sun!
pressure from table
weight from gravity
pressure from hot gas
weight from gravity
temperature: random motion of atoms in a gas
pressure: amount of force per unit area on piston from gas
generally pressure increases with increasing temperature
Balancing Fusion, Gravity and Pressure
If the rate of fusion increases, then:
thermal pressure increases causing the star to expand.
star expands to a new point where gravity would balance the thermal pressure.
the expansion would reduce compression of the core
the temperature in the core would drop
the nuclear fusion rate would subsequently slow down
the thermal pressure would then drop
the star would shrink
the temperature would rise again and the nuclear fusion rate would increase
Stability would be re-established between the nuclear reaction rates and the gravity compression
balance between pressure, heat from fusion and gravity determines Sun's size
big stars have cooler cores, small stars have hotter cores – more compressed
Helium is not the only product in the fusion of hydrogen.
Two other particles produced
Positrons quickly annihilate with electrons.
Photons produced in core of the Sun take about a million years to move to the surface.
Slow migration because they scatter off the dense gas particles
move about only a centimeter between collisions.
In each collision, they transfer some of their energy to the gas particles.
As they reach the photosphere, gamma rays have become visible photons.
Nearly massless particles with no charge.
Rarely interact with ordinary matter.
Neutrinos travel extremely fast
Almost at the speed of light if small mass.
Neutrinos pass from the core of the Sun to the surface in only two seconds.