Originally posted by surfup
Could you please? Thanks
no problem what so ever. here goes.
Zero Age Main Sequence (ZAMS)
-once stars enter the main sequence, they have varied lifetimes, due to mass.
1 solar mass (such as our sun) -> 10 billion years
.5 solar mass (such as a red dwarf) -> 200 billion years
3 solar mass (smaller giant stars - under chandrasekhar limit. i'll get into that later) -> 500 million years
10 solar mas (larger giant stars) -> 50 million years
-there are two types of stars - population I and population II.
population I stars are newer stars that are "metal rich," meaning they have lots of chemical elements. they can be found throughout the spiral arms
of galaxies. they're also stars that are several generations old, meaning made up of from remnants of many supernovae.
population II stars are older stars that are "metal poor." they can be found in globular clusters in the galactic halo, which is the space around
the center of the galaxy.
most stars in this stage of their existence are variable stars, so i'm going to focus on them.
Variable Stars
variable stars are stars that very in brightness. in excess of 50,000 are known and more are discovered every day with new techniques.
there are several types of variable stars.
- eclipsing binaries -> binary stars where a dimmer binary star orbits around the main star, eclipsing it on view to earth. pretty much self
explanitory by the name.
- pulsating variables -> two main types, cepheids and rr lyraes
- cepheids -> all F to G class stars on the main sequence going through the "instability strip." this is when a star is becoming a giant, and is
pulsating rapidly as it expands and contracts. they have anywhere from a 2-100 day period of max to max luminosity, with the brighter the star the
loner this period is.
- rr lyraes -> they are similar to cepheids, except that they are found only in globular clusters
- other variables
- long period -> red giant stars, with an 80-500 day period. they have a wide range of magnetude.
- semi-regulars -> red supergiants ending thier life. possibility to go supernova at anytime, basically.
- t tauri -> the newly forming stars
Sequence of Stellar Death
the mass of the star will seal its fate. with the deaths of more massive stars new chemical elements are created. as a star dies its fusion process
has to go to higher and higher elements. this is the sequence of fusion (called chemsynthesis):
H -> He, He -> C, C -> Ne and MG, Ne -> O and Mg, O -> Si and P, Si -> Fe. when a star begins to fuse iron into higher elements is when it dies.
Death of Low-mass Stars (up to 1.4 solar mass)
- these are stars that are below the chandrasekhar limit. this is the limit which when a star above will go nova.
- when the helium to carbon process begins, the star expands into a red giant. when this happens to the sun, it will expand to nearly the earth's
orbit. this swelling then lowers the star's density, but it also increases the luminosity due to the immense surface area.
- when the star reaches the silicon to iron process it blows off all of its outer layers (about half its mass) in a great stellar wind. this forms a
planetary nebula. this stage lasts around 50,000 years. at the center of this is a white dwarf star.
- the white dwarf left over is a small, dense corpse that is only supported by degenerate matter, which is the mutual repulsion of electrons (likes
repel). it's roughly 3 times the size of the earth.
Death of Medium-mass Stars
- medium mass stars are stars with a mass above 1.4 solar masses to 3.0 solar masses. they follow the same process of turning to red giants when
helium becomes fused into carbon.
- when the silicon becomes fused into iron though, the star begins to collapse in on itself. this collapse triggers the HUGE energy release known as a
supernova. this explosion fuses more elements from the iron in a fraction of a second. also, the intesnse temperatures at the core of the star fuses
the electrons and protons into neutrons, creating a neutron star.
- a neutron star is equivilant to the mass of the sun shrunk into an area 10 to 15 miles in diameter. due to the extreme density there is a very rapid
rotation, creating a pulsar.
Death of High-mass Stars
- stars that are above 3 solar masses
- instead of a neutron star forming, the star continues to collapse in on itself and forms a blackhole.
sorry this has taken me so damn long. i gave up on procratinating and am working on an english paper at the same time. if there's anything more or
something you don't understand, just ask!
