How Does a Star Die?
Written by Katrina Cain
Question: How Does a Star Die?
Answer: So a star has reached middle age by fusing hydrogen into helium. Then what happens? Once a star has run out of usable hydrogen that it can convert into helium, a star then takes one of several paths.
If the star is 0.5 solar masses (half the mass of our sun), electron degeneracy pressure will prevent the star from collapsing in upon itself. Due to the age of the universe, scientists can only use computer modeling to predict what will happen to such a star. Once it has finished its active phase (hydrogen to helium), it becomes a white dwarf.
A white dwarf can come about in one of two ways; first, if the star is very small, electron degeneracy pressure simply stops the collapse of the star, it is out of hydrogen, and it becomes a white dwarf. Secondly, and more commonly, the core of the star can still be surrounded by some layers of hydrogen, which continue to fuse and cause the star to expand, becoming a red giant.
A red giant is a star in the process of fusing helium to form carbon and oxygen. If there is insufficient energy to make this happen, the outer shell of the star will shed leaving behind an inert core or oxygen and carbon - a remnant white dwarf. If enough energy is involved in the casting off of stellar casings, a nebula can form. If said white dwarf is in a binary system, it could become a type 1A supernova, but this is very rare. Instead, it is thought that a white dwarf will eventually cool to become a black dwarf - in theory because there are no white dwarfs older than the universe, black dwarfs are theoretical only because there hasn't been enough time for one to form.
If a star that has reached the end of its productive phase is below the Chandrasekhar Limit - 1.4 times the mass of our Sun - it will become a white dwarf; over this limit, it will become a neutron star. If a star is larger than about 5 times the mass of the sun, when the hydrogen fusing stops, a supernova will take place and the rest of the material will condense into a black hole.
Filed under: Astronomy, Questions
May 24th, 2008 at 3:34 am
Hi Katrina
Star death is quite a complex process at the extreme ends of the Main Sequence. Stars below about 0.2 solar masses won't form red giants and they won't fuse their helium 4 either. Instead they convect their whole hydrogen envelopes, eventually fusing the lot, slowly brightening before fading out as a helium dwarf.
Stars between 0.2-0.3 solar masses do puff up and above 0.25 solar masses a red giant stage is reached. Above 0.3 solar masses and helium fusion can occur in the core. As the stars get bigger more and more of their mass is blown-off in the red giant and asymptotic giant stages - our Sun will lose ~46% of its mass before becoming a white dwarf. Higher mass stars burn carbon, then carbon's waste products, but they also dump a lot of mass back into the interstellar medium. Only stars above 8 solar masses retain enough core mass to go supernova and form a neutron star core. And stars above about ~ 30 solar masses form black holes, with an associated gamma-ray burst caused by a massive, short-lived accretion disk that is engulfed by the hole.
Gravitational energy liberated by a black hole or a stellar core collapse can be vastly more than the fusion of the star itself. Infall into a black hole releases ~5.7% of the mass-energy - over 6 times the energy released fusing hydrogen all the way into iron. No wonder gamma-ray bursts are so bright!
May 30th, 2008 at 12:24 am
What is the hottest surface temperature star in our galaxy and where? How does it stack up against our Sun in size age and temp?
June 21st, 2008 at 10:31 am
what would happen if 1 old star explose right next to a young star
August 28th, 2008 at 7:47 pm
It depends on the star. Some die of old age, or just fade out never to be seen in a decent movie again. Recently however there have been a number of bad drug overdoses; resulting from a life of partying too much.
Ok you'll probably delete this, but it HAD to be said.. sorry.. LOL
September 30th, 2008 at 9:25 am
is pluto is a planet?
October 24th, 2008 at 3:54 am
Pluto is considered a Dwarf planet meaning it has enough mass to pull itself into a spherical shape by gravity but has not managed to clear itself away from space debris around it ie smaller planetismals and asteroids. Also this means it is not a moon, ie it does not orbit another planet. Pluto does however have moons the largest being called charon which is nearly as big as pluto itself, but not quite.