Astronomy

The main sequence (hydrogen core burning) lifetime for stars like the sun.

10 billion years

Helium flash

An explosive event in the post main sequence of a low mass star (our sun). the core is extremely dense (compacted by gravity the helium is 10,000 times denser than any thing we have on earth!) but the fusion in the core is explosive and continues until the core is pushed out and the star is in equilibrium again. This signals the end of the red giant phase.

Stage 9 =

Red giant

red giant surface temperature and radius

Surface temp = decreasing ; radius = increasing

Main sequence turnoff

The high luminosity end of the observed main sequence.

Hydrogen shell burning

When the hydrogen goes through fusion in the core helium is left in the core. The temperature is not hot enough for the helium to "burn" (go through fusion) so it starts to shrink because it cannot put out any pressure to counteract the gravity. When the gravity pushes in, the core heats up and causes the central temperature of the star to rise. This in turn heats up the overlying layers of hydrogen. This heat caused by the helium is so hot that the hydrogen burns faster than before.

temperature of 10^7 K

needed to fuse hydrogen into helium

the main sequence equilibrium is a result of?

out ward pressure of hot gas and the inward pressure of gravity.

Nova

a star that suddenly increases in brightness, often by a factor of as much as 10,000. then slowly fades back to its original luminosity. this is the result of an explosion on the surface of a white dwarf star, caused by matter falling onto its surface from the atmosphere of a binary companion.

increasing radius in a star =

increasing luminosity in the star

Core hydrogen burning

the core stage in main sequence stars in which hydrogen is "burned" in nuclear fusion in the central region of the star. this reaction produces helium. the star spends up to 90% of its lifetime in hydrostatic equilibrium.

planetary nebula

the ejected envelope red-giant star, spread out over a volume roughly the size of our solar system.

Stage 11 Red Giant....Again?

the fist shell is hydrogen the second now helium surrounding a carbon core this core gets compacted by the gravity and becomes so hot that it pushes out again like it did before, only this time even more because of the two shells it has more energy to push with.....Swol. The luminosity increases as well. Asymptotic giant branch.

Stage 10 the horizontal branch

the star is at a stage of hydrostatic equilibrium. burning helium in the core and fusing hydrogen in a shell over the core. In the branch the stars position is mainly determined by the mass (more mass to the right, less mass to the left)

Sub giant branch (stage8)

this is a section on the evolutionary track of a star. Just after hydrogen stores are depleted in the core. Hydrogen shell burning takes place, which causes a general expansion of the stellar envelope.

Red giant branch

this is a section on the evolutionary track of a star. The hydrogen shell burning forces the star to get larger and larger and then the radius of the star becomes so large that the outer core cools off. This is a red giant.

gravity and pressure in a star

usually an equilibrium