Death of Stars

[Belgian General]

Hey there. I've been doing some reading on stars lately (wikipedia, nothing really serious, just out of curiosity) but I'm in some trouble. I don't really understand how stars die. Apparently after a certain amount of time they lack hydrogen or helium, I forgot, and can't proceed to do a certain reaction. Upon which they start shedding outer layers?
I know lots of people on here are smart, perhaps they can explain me. I'm a bit confused right now. It also seems to take multiple stadia; red dwarfs, white dwarfs, and such things. What's the distinction?

Thanks in advance.

[Simetrical]

I don't know much astronomy, but the general point is that stars tend to stay the way they are because of energy created by nuclear fusion. Fusion changes lighter elements into heavier elements, which are much harder to fuse. Once a large enough percentage of the light elements in the star (e.g., hydrogen and helium) are fused into heavier elements, there's not enough material to fuse, and the star's former state is no longer stable.

I don't know much more than that, though.

[Juvenal]

Most^[EDIT] stars spend most of their lives on the Main Sequence.

During this time, they have a core of fusing hydrogen surrounded by non-fusing plasma.

Thermal pressure from the fusion acts against gravity, keeping the star in hydrostatic equilibrium.

When there is no longer enough hydrogen in the core to support fusion the star leaves the main sequence. What happens next is determined by the star's mass.

Stars smaller than 0.23 solar masses (red dwarfs) become white dwarfs, no longer fusing, and radiating by means of stored heat.

Stars of 0.5 to 6 solar masses pass through a red giant stage with a shell of fusing hydrogen around an inert helium core. Bigger red giants may start to fuse helium into carbon at the core. Bigger ones still can have further levels of fusion of higher weight elements. Red giants eventually run out of fusion fuel and collapse into white dwarfs, ejecting their outer layers as a planetary nebula.

Stars of greater than 10 solar masses can develop fusion shells all the way up to nickel/iron. Fusion into heavier elements than nickle actually absorbs energy, so development of a nickel/iron core leads to core collapse and possibly a Type II supernova. The remains of the supernova becomes a neutron star, or if heavy enough, a black hole.

[Belgian General]

Thanks. I always prefer people explaining stuff to me over wikipedia, it's a way more personal approach and helps me understand. +rep for both.

[Misery]

I would like to add to wonderful post by Juvenile (+ rep for that) that it has been theorized that death of a stars with approximately 40 solar masses would result in hypernova that would result in complete destruction of the star, without creation on neutron star (pulsar) or black hole.

Stars of such a such a large mass where only possible shortly after big bang and formation of the galaxies and are believed to be first generation of the stars which originally seeded galaxy with heavier elements.

Black Dwarf - Cooled off white dwarf, but as it takes approximately 13.7 billion years for white dwarf to cools down so it no longer emits light these will not exist for foreseeable future.

White Dwarf - Dead star approximately size of the earth (each tablespoon of matter would equal around billion tons). responsible for type 1a supernova which are greatest tool when it comes to measuring distances between galaxies.

Brown Dwarf - failed star that did not have enough material to kick start nuclear fusion, largest ones are approx .0075 solar masses. Very hard to see due to low luminosity.

Red Dwarf - Smallest possible star, most numerous in universe, max size .5 solar masses. Majority of light produced is in red spectrum, really cool stars (well by other star standards) long life spans (NO red dwarf that was ever created in universe died, they are all still in their infancy.

Blue Dwarf - Theoretically once red dwarfs burn their hydrogen reserves they will increase their luminosity (all stars get brighter as they get older) and become bluer. this will not occur for approximately 1.5 trillion years

Orange Dwarf - .5 -.8 solar masses. Alpha Centuri B is Orange dwarf. life span 15 - 20 billion years

Yellow Dwarf - well open up window, put sunglasses and look up during fine day, you will see one. (Did you know that our sun actually shines white not yellow color)

[Godfrey I of Leuven]

Some nearby Supernova candidates:

-Betelgeuse (Orion)+
-Eta Carinae (Carina)
-Antares (Scorpius)+
-Spica (Virgo)+

All of these stars are quite bright so should you be interested you can always go and look outside (stars with + are visible in the Northern Hemisphere). And ofcourse all 4 of these stars are said to go supernova in the 'near' future which could be this evening or in a thousand years ( I'd put my money on Betelgeuse to go first though )