In high mass stars degeneracy pressure is not an issue because their core temperatures are so high that thermal pressures remain strong. There is no helium flash in high-mass stars. Because of this process the helium core fusion ignites gradually, the same as when hydrogen core fusion did at the beginning of the stars life. This process of fusing helium into carbon will last only about a few hundred thousand years. The supergiant star will be left again without energy. If the star has no energy there will be nothing to help with the crush of gravity. The density, temperature, core pressure all raise because the inert carbon core is shrinking and the crush of gravitational forces rise. Between the inert core and hydrogen -fusing shell another shell forms, a helium-fusing shell. The core that is continually being crushed by gravity and is shrinking away is also becoming hotter and hotter. It will eventually be hot enough for carbon fusion to ignite. This process can continue over and over creating new energy with new shells. For example other elements that can be created by this process is carbon into oxygen, oxygen into neon, neon into magnesium, Each time a new fusion begins the core of the star shrinks and get even hotter. Eventually iron begins to build up. Iron is special because this element can not generate nuclear energy. This iron is going to break down and collapse releasing an enormous amount of energy and blasting all the layer and layers of shells it had produced, into space. With out high-mass stars the elements that have been created and scattered would not have come together to build our Earth and us. The processes of making these elements only happen in high-mass stars because they are hot enough to produce the next step. Low-mass stars have degeneracy pressure that halts the process before the core could get hot enough (Bennett, Donahue, Schneider & Voit, 2012, p.348-351).
When the dying star finally gets hot enough to create the element iron and iron can't continue the nuclear fusion process a supernova explosion will follow. The energy that has been building up layers upon layers throughout the previous supergiant life, are blasted off into space. What is left behind is a ball of neutrons called a neutron star. If the neutron star that is left behind has a very large mass, gravity may overcome neutron degeneracy pressure which could then collapse into a black hole. By using theoretical models, scientists can create their own supernovae explosion and study what the exact trigger may be. What we know today about the study and understanding of supernovae is also due to decades and cultures. For example the supernovae remnant is a cloud of debris in which a spinning neutron star lies in the middle. Over many years of photographs scientists have calculated that the nebula is growing larger and larger. If scientists calculate backwards they can pinpoint the history of this star. In this example Chinese observers recorded a guest star in this location in 1054. This could have been the supernova that created this nebula (Bennett, Donahue, Schneider & Voit, 2012, p.3512-352).
Degeneracy pressure is important to white dwarfs because this is what keeps the white dwarf from collapsing. In a white dwarf there is no longer any fusion to maintain the heat and pressure that is coming in from gravitational forces; therefore there must be some other type of force (degeneracy pressure) that is fighting the battle against the crushing gravity, still giving the white dwarf a look of a stellar object. Degeneracy pressure actually supports brown dwarfs as well and when this pressure arises from closely packed electrons in white dwarfs it is called electron degeneracy pressure. This pressure balances the inward crush of gravity. As we have learned what is left of a high-star that has lived its life is a collapsed iron core now a ball of neutrons named as so, a neutrons star. Just as a white dwarf that is fighting the inward pressures of gravity, so is a neutron star. This pressure is also a degeneracy pressure, which fights against the gravitational forces when elements are packed closely together. In the case of a neutron star the pressure is called a neutron degeneracy pressure. A paperclip that has the density of a neutron star would outweigh Mount Everest, because of this density it would pass through the Earth and the Earth's center would resemble swiss cheese (Bennett, Donahue, Schneider & Voit, 2012, p.363-369). White dwarfs and neutron stars have their own mass limits just as do black holes and other stellar matter. The mass limit of any one type of objects in important for classifications of families. In the case of a white dwarf their limit is 1.4Msun, otherwise known as the Chandrasekhar limit (Bhattacharya, 2011).
In a close binary systems white dwarf can gradually gain mass if its companion is a main-sequence or giant star. The gas from the companion star can fall toward the mass of the white dwarf. The falling matter forms a whirlpool like disk around the white dwarf because the law of conservation of angular momentum states that as the gas matter get closer and closer to the surface of the white dwarf it rotates faster and faster. This could only happen in a binary system because the companion star is the key ingredient to where the rapidly rotating disk called the accretion disk comes from. Nova comes from this whole equation also, as these hydrogen gases are being drifted toward the white dwarf and then gases fall to the surface of the white dwarf, gravity eventually makes a thin layer. Over time as layers build up and temperatures begin to rise within the white dwarf core once again it will create a big blaze of light that may shine for a few weeks. When this star comes back to life it is called a nova. Without a binary system were you have a white dwarf and a companion star you would not have the accretion disk caused by the companion star. Without the accretion disk and all the gaseous matter falling onto the surface of the white dwarf you would not have a heated core that would spark the nova. A supernovae remember in when a high-mass star is at the stage were it has produced an iron core and when the core collapses it explodes the layers of the star out into space (Bennett, Donahue, Schneider & Voit, 2012, p.351-352).
A supernova is much brighter than what a nova would shine, but nova are still very bright. They can shine as bright as 100,000 Suns. When a nova takes place we can see it from Earth. In some cases they have repeated their nova blasts just after a few decades, this reinforces the fact that this nova is being fed by a companion star in a binary system (Bennett, Donahue, Schneider & Voit, 2012, p.366-367).
Singularities and the Event Horizon
Singularity, the Schwarzschild radius, and Event Horizon all have in common that they push our limits about what we currently know in the subjects of physics and scientific knowledge. Singularity is at the point of a black hole in which all matter that took place in forming the black hole was to be crushed to bits and pieces that are tiny to a dense point somewhere in the center of the black hole. Before you get anywhere near the center of the black hole you have the event horizon which is the boundary line between the inside of the black hole and the universe. The event horizon is like a bottomless pit, and anything that goes in will never be seen again. It is a boundary not a vacuum as I once had thought. Gravitational forces are at play but not so much that you would be sucked into this black hole if you go anywhere near its outer vicinities. It is hard to imagine the size of a black hole. To figure out what the size of a event horizon could be, you would be looking for the Schwarzschild radius. The Schwarzschild radius of a black hole solely depends on the mass of the black hole itself. For example for a mass like that of our Sun we would say the Sun would have a Schwarzschild radius of 3km. The more massive the object the larger the radius will be. The mass of a stellar core must be greater than 3 solar masses to have the chances at creating a black hole. This is so because at the point of 3 solar masses according to the laws of physics there is nothing that can stop the collapse of a stellar corpse. As we recall the larger the stellar mass of the black whole is the larger the Schwarzschild radius will be (Bennett, Donahue, Schneider & Voit, 2012, p.376-377).
Black holes may have a larger radius subject to what there stellar masses are but a black hole can also increase in size by accreting matter from their surroundings. Only the lowest angular momentum material will be available to feed the black hole (Power, Nayakshin, & King, 2011). If what scientist are thinking is true that a black hole starts from the process of the death of a star then we would find black holes throughout the galaxy because primordial stars could have dies anywhere in the galaxy. Astronomers have know for over ten years that pretty much every galaxy they have found has some type of black hole in them. Black holes have been around for many years, the oldest black holes every found is about two billion solar masses and formed around 13 billions years ago which was only 770 million years after the big bang (Greene, 2012).
References:
Bennett, J., Donahue, M., Schneider, N. & Voit, M. (2012) The essential cosmic perspective. (6th ed.) San Francisco, CA: Pearson Addison-Wesley
BHATTACHARYA, D. (2011). Beyond the Chandrasekhar limit: Structure and formation of compact stars. Pramana: Journal Of Physics, 77(1), 29-37. doi:10.1007/s12043-011-0109-0
Power, C., Nayakshin, S., & King, A. (2011). The accretion disc particle method for simulations of black hole feeding and feedback. Monthly Notices Of The Royal Astronomical Society, 412(1), 269-276. doi:10.1111/j.1365-2966.2010.17901.x
Greene, J. E. (2012). GOLDILOCKS BLACK HOLES. Scientific American, 306(1), 40-47.
