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The energy released by fusion in the core of a star produces an outward pressured force that counteracts gravity. When fusion stops, that force goes away and gravity takes hold, causing the core to collapse.
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What is a limiting factor to the amount and type of fusion that occurs in stars?
The mass of the star and the related temperature of the stellar core determine the thermonuclear process type of the star. The stars of the solar mass produce energy from Hydrogen in the proton-proton cycle (two and three proton nuclei appear in intermediate stages of the fusion, end product is Helium); stars twice (or more) as heavy run the HNC cycle (Although Helium is here still the end product, Nitrogen and Carbon appear in intermediate fusion stages, too). Once the Hydrogen is used up, gravity collapse makes the temperatures rise until the next , heavier element fusion cycle is activated. As the temperature rises, other numerous fusion cycles can produce all existing elements. The heaviest ones are created in the extraordinary high temperatures of the supernovae-explosions
How are supernovas formed?
Supernovas are formed in two main ways. First, in a binary star system, when one star becomes a white dwarf and accretes matter from its companion, it can reach a critical mass and undergo a thermonuclear explosion, creating a Type Ia supernova. Second, in a massive star, once nuclear fusion in its core stops, the core collapses under gravity and then rebounds, resulting in a massive explosion and the formation of a Type II supernova.
When a low mass star first runs short of hydrogen in its core it becomes brighter because?
Low mass stars become brighter after depleting hydrogen because all of the hydrogen in the core has been fused into helium. Once this happens, hydrogen fusion begins in the outer layers, which causes more heat and light generation.
What are the Stages of a star?
nebula then protosar then red dwarf, yellow star or a blue giant then a red giant then a red super giant then eithr a white dwarf or a supernova from the supernova a black hole or a neutron star if it is a white dwarf it turns into a black dwarf then a black holeNebulaBaby starStarGiant or supergiantWhite dwarfBlack dwarf
What determines whether a star will form a black hole when it dies?
The mass of the remaining core of a star that has exploded as a supernova. (Although some stars can collapse directly to a black hole without a supernova explosion)If the mass exceeds about 3 to 4 solar masses the degeneracy pressure of neutrons is insufficient to stop the collapse, and the object will inevitably collapse into a black hole.See related link for more information.
What happens to a massive star when its fusion period is over?
Once a star's nuclear fusion has ended, it will collapse inside its core and become what is known as a white dwarf. Its outer layers will shoot out into the universe as planet nebula. If they are very large, stars will explode into a Supernova and their core will collapse into a black hole.
Why is the fusion of iron a problem for a star?
Unlike all lighter elements, fusing iron consumes more energy than it produces. Once a star's core starts iron fusion it stops producing energy and collapses. The collapse then blows away the outer layers of the star in a massive explosion called a supernova.
What keeps stars core hot enough for hydrogen fusion?
Initially, a star's core is heated by compression as a nebula collapses. Once fusion is up and going, the fusion itself provides the necessary heat.
A protostar forms once the nebular cloud condenses and the core begins?
nuclear fusion
What are large stars that explodes in supernovas but are not big enough to form a black hole?
Neutron stars are as close as you get to a black hole without being a black hole. When a star of 25 or more solar masses depletes all of its fuel, it will be unable to counterbalance its own gravity through nuclear fusion or quantum degeneracy and the core will implode (Collapse) releasing a large amount of matter. Once its a few hundred kilometers in radius, quantum degeneracy stops the collapse. Any more than 3.2 solar masses and it will fully collapse into a singularity.
Explain why the sun does not collapse under the force of its own gravity?
Stars do not collapse because the inward force of gravity is balanced by the pressure generated by fusion. When stars die they do collapse. The cores of low to medium mass stars collapse to form white dwarfs. Further collapse is prevented y electron degeneracy pressure. More massive stars leave behind neutron stars, in which gravity is balanced by neutron degeneracy pressure. In the most massive stars, once fusion stops producing energy there is nothing to stop the collapse and the core becomes a black hole.
Why is mass important for a supernova?
Stars produce energy through nuclear fusion, producing heavier elements from lighter ones. The heat generated by these reactions prevents gravitational collapse of the star. The star builds up a central core which consists of elements, where the temperature at the centre of the star is not sufficient to fuse them. For main sequence stars with a mass less than about 8 Suns, the mass of the core will eventually lose mass as planetary nebulae until only the core remains. Which becomes a white dwarf.Stars with higher mass will develop a degenerate core where the mass will grow until it exceeds the Chandrasekhar limit [See Link]. At this point the star will explode in a core collapse supernova, leaving behind either a neutron star or a black hole.For Type II supernova [See Link] [See related] mass flows into the core by the continued making of iron from nuclear fusion. Once the core has gained so much mass that it cannot withstand its own weight, the core implodes. This implosion can usually be halted by neutrons (the only things that can stop a gravitational collapse). When the mass of the star is so great even neutrons fail. The collapse is abruptly stopped by the neutrons, matter bounces off the hard iron core, and turns the implosion into an explosion.For Type Ia supernova, [See Link] [See related] the energy comes from the runaway fusion of carbon and oxygen in the core of the white dwarf.
Why do stars cool when the fusion cycle gets to iron?
Unlike lighter elements, fusing iron consumes more energy than it produces. This does not, however, cause a star to cool. Once a star gets to the point of fusing iron, the core stops producing energy and without the pressure from the heat it produces, the core collapses while the rest of the star is blasted away in an explosion.
What force is responsible for crushing or collapsing stars?
A supernova is caused the the fusion of (in most cases helium) molecules in iron. Once you reach iron, you can't use fusion. Thus, the star can't produce the energy to keep it stable and gravity causes it to collapse.
What is a carbon fusion?
Carbon fusion is a stage towards the end of a star's life. See para below and link Carbon burning starts when helium burning ends. During helium fusion, stars build up an inert core rich in carbon and oxygen. Once the helium density drops below a level at which He burning can be sustained, the core collapses due to gravitation. This decrease in volume raises temperature and density of the core up to the carbon ignition temperature. This will raise the star's temperature around the core allowing it to burn helium in a shell around the core. The star increases in size and becomes a red supergiant.
When does a protostar becomes a main sequence star?
As the gases in a protostar begin to collapse, the central core begins to heat up due to pressure. As more gases are absorbed, the greater the pressure. Once the temperature of the core reaches 10 million degrees K, hydrogen fusion begins, and the star begins it's life on the main sequence. The star will stay on the main sequence whilst it still has hydrogen to fuse. Once all the hydrogen has been used, the star will drop out of the main sequence. Protostar stage in the stellar evolution. [See related question]
How scientists believe then black hole occurred?
By the gravitational collapse of a star of sufficient mass. Once the star stops producing energy, the radiation pressure decreases, and it can't maintain itself against its own gravity.
