What happens when hydrogen fuel runs out of a main sequence star?

Answer 1

After the core of a massive star exhausts its hydrogen, fusion moves to the shell around the core. Later, helium fusion will ignite in the core. In a series of stages the core will fuse progressively heavier elements until it reaches iron. Unlike all lighter elements, fusing iron absorbs more energy than it releases. As a result the core will collapse into either a neutron star or a black hole while the rest of the star is blasted away in a supernova.

Answer 2

It does not go out. Hydrogen is the main fuel of normal stars and will burn for the majority of its luminous lifetime. Unless I remember incorrectly -- after the hydrogen is used up the star collapses under its own weight and the next element to combust under all this new pressure is helium. The Hydrogen-helium Phase results in a color shift.

Ryan92394 adds:

Different stars do different things. A small or medium sized star, like our Sun, will shrink slightly creating massive amounts of internal heat. Hydrogen fuses into helium at around 18 million kelvin. Then After all the hydrogen in the core is spent the contractions of the star will eventually heat the core to 100 million kelvin which is the temperature that helium fuses into carbon. This results in a large explosion known as a carbon flash. After this point the star will remain stable for another few million years, but since it is much hotter at the core the star balloons outward and becomes a red giant. After this point the star eventually ejects all the plasma that it held outside its core into space, and this becomes a planetary nebula (no relation to planets at all) and the end product is a white dwarf star. Larger stars will continue to get hotter and hotter and keep fusing heavier and heavier elements in a shell around the core like layers of an onion. Once the large stars fuse all the way to Iron all fusion stops because Iron doesn't create energy and cant be fused into anything heavier inside of the star. At this point the star collapses in on itself then explodes into a Supernova which is a burst of fusion outside the star that fuses all off the heavier elements that we are made of than after ejecting all matter around the core and due to neutron degeneracy pressure the core will become a neutron star, or the super massive stars create a Stellar Mass Black Hole.

Answer 3

It still remains a star. After a star runs out of hydrogen to fuse into helium, it begins fusing the helium. It continues fusing these progressively heavier elements until it gets to iron. At this point, it cannot fuse the iron into heavier objects and the star dies. How the star dies is really a matter of it's size, but that is another question.

Answer 4

A star has to be a minimum of about 8 times the mass of our Sun to go supernova.

Actually, we are probably talking about what is technically called a

Type II (type two) supernova. This is the second most common sort of supernova.

What happens inside the star is a little complex.

Initially the star fuses Hydrogen into Helium, exerting and outward force that is kept balanced by gravity. This is called Hydrostatic Equilibrium.

When the Star runs out of Hydrogen to fuse the outward force stops and the core begins to collapse.

Eventually enough heat is generated to start the fusion of Helium into beryllium and carbon, creating a cooler fused hydrogen outer layer and a hotter Helium core. This process is repeated over and over until the star has a core of iron.

To fuse iron into heavier elements requires more energy than is generated, so the star collapses one final time and dies in a massive outburst of energy, throwing all the outer layers away in what we see as a supernova.

At this point some of the heavier elements are produced as well, like gold etc.

The star then can have 1 of 2 fates.

If what remains of the core, after the explosion, has more than about 1.4 times the Sun's mass (but less than about 3 times the Sun's mass) it will collapse into a neutron star.

If it has more than about 3 times the mass of the Sun, then it will collapse in on itself, creating a gravity well we call a Black Hole.

Answer 5

When a star's core begins to run out of hydrogen and fuse helium instead, this is known as the red giant stage. Basically, the star surface expands so the star actually becomes less dense (density = mass/volume). This is what will happen in our sun in approximately five billion years. Eventually, the helium will all be fused into heavier elements such as carbon and oxygen.

Answer 6

The hydrogen in the core of a star is never ALL converted to helium; even in an old star, it's about 40-50% hydrogen. But as the proportion of helium increases, it interferes with hydrogen fusion.

Helium is like the stellar "ashes" in the bottom of the fireplace. Keep your fire going long enough without shoveling out the ashes, and the ash will smother the fire, even if there's still lots of wood left. This is very similar; when it takes four protons (four hydrogen nuclei) to come together to fuse, it doesn't take a whole lot of helium to mess things up.

Eventually, the nuclear reaction starts to decline. But the outward pressure of the nuclear reaction is the only thing balancing the INWARD force of the star's tremendous gravity, and the star begins to collapse. As it collapses, the pressure and temperature goes up. If it goes up high enough, then the helium "ash" in the star begins to fuse on its own, to produce carbon and oxygen. This sudden RUSH of energy causes the star to expand into a red giant.

Answer 7

Stars don't actually "use up all their hydrogen". In a normal star, hydrogen is fused into helium, generating energy.

The helium builds up in the core of the star like ashes in the bottom of a fireplace. If you cover the logs in a fireplace with ashes, it will put out the fire even though there is still plenty of wood, and the helium in the core of the star, as it becomes more and more plentiful, begins to interfere with the hydrogen fusion. The hydrogen atoms keep bumping into helium atoms rather than other hydrogen atoms, and the reaction begins to slow down.

A star is extremely massive, and its own gravity causes it to crush itself; the energy generated by hydrogen fusion keeps the star from collapsing. When the energy of fusion decreases, the star begins to collapse. This collapse causes the core of the star to be compressed, and this compression also generates heat - ask any Scuba diver what happens when he fills his tanks. So the increased pressure and temperature in the core continues to rise as the star collapses.

At some point, the temperature and pressure of the stellar core becomes SO great that the helium itself begins to fuse, this time into carbon. Instead of fading and collapsing, the star generates so much MORE heat that it expands enormously, into a red giant star.

For a star like our Sun, that's the last stage; as the helium is burned up and the carbon builds up in the stellar core, eventually the fusion reaction fades out and the star once again begins to shrink. It will become a white dwarf star, fading slowly through billions of years.

For a fairly massive star, there is another stage; when the helium is depleted, the star collapses and becomes so hot and dense that it begins to fuse the carbon into even heavier elements. This releases SO MUCH energy, SO QUICKLY, that the star explodes in a nova or supernova explosion. The core is crushed into a neutron star or black hole, while the middle and outer layers of the star are blasted back into space! That's where we come in, because the carbon and iron atoms and other heavy elements of our Earth and that make up our bodies was produced this way, and blasted back into space where it became part of the stellar nebula that formed our solar system.

Answer 8

The star becomes a red giant, because its luminosity increases while its surface temperature decreases due to the expansion

Answer 9

After this, The star has nothing else to survive on, causing it to change into a black hole

Answer 10

it blows up and if it is strong enough it can create a black hole