All of these bodies are related to each other in the evolution of stars. Sort of like the difference between a baby, a teen, middle aged adult and a senior! Stars from out of nebulae, which are dispersed gases floating in enormous regions of space. Gravity starts to draw these gases, mostly Hydrogen and Helium, together and when enough mass collapses together, nuclear fusion takes over and the star lights up.
If the mass of the star is on the smallish side, it will eventually become a Red Giant later in its life - this is the future of our own sun in about billion years. Near the end of a smallish star, it will again spit out gases and matter into another nebulae and eventually contract to a white dwarf star.
If the original mass of the star was large, it will eventually form a Red Supergiant star. The main effect is the ability to again start nuclear fusion reactions. The nuclear reactions which happen are quite fast, and the resulting pressure wave will swell the peripheral layers of the star.
This phenomenon is called "shell burning". During this time, the core will continue contracting under the effect of gravity, and it will transfer its energy to the surface of the star, which will inflate further, and so become cooler.
The diameter of the star can increase by a factor of , while its cooling is translated into a reddening of its radiation : the star is becoming what is called a red giant. By collapsing, the core gets hotter and hotter.
If the temperature can rise up to million degrees, the nuclei of helium are able to merge together to form unstable nuclei of berylium. These nuclei, in their turn, merge to form carbon, which is stable this reaction is called the " triple alpha " process. This reaction can only occur if the mass of the star is greater than half of the mass of the Sun. This very fast phase is called the "helium flash".
At this time, the energy is produced as a very high rate, and this allows the star to keep its equilibrium. If the mass of the star is less than 1.
The carbon kernel becomes lifeless, the fusion processes are slowing and the star gently begins to switch off. Considering the requirement over the mass of the core, all this applies to stars whose initial mass is less than a few solar masses. If a white dwarf is part of a binary system then the crust may be stripped away, exposing the core. This is what happened to PSR J b, which is known as a diamond planet discussed in Chapter White dwarfs are expected to keep radiating for well over 14 billion years, however, and so the universe is not yet old enough to contain any.
Copyright Privacy Disclaimer Search Sitemap. I Pre 20th Century theories 1. Constellations 2. Latitude and Longitude 3. Models of the Universe 4. Force, Momentum, and Energy 5. The Origin of the Universe Galaxies Stars Red Giants and White Dwarfs Supergiants, Supernova, and Neutron Stars The planet Mercury The planet Venus The planet Earth The planet Mars The Asteroid Belt The planet Jupiter At this point, the star inflates and becomes a giant or supergiant depending on size.
As the star continues burning through Helium, Beryllium, Carbon and Oxygen, the core contracts and expands through each of the fusion processes.
Only stars more massive than our Sun approx. As the Star burns through more Helium, it expands into an Asymptotic Giant Branch AGB star and begins to vary its size and brightness as different shells of hydrogen and helium are burned and helium flashes occur.
The core of the star is becoming more unstable as time goes on. Interestingly, the Helium burning shells in the star can begin synthesizing heavier elements due to neutron capture and beta decay to produce elements as large as Bismuth Also, Carbon and Oxygen are transported from inside the star to the outer atmosphere due to powerful convection currents.
Stars with greater mass than our Sun greater then 5 solar masses begin by burning helium in the core much like a solar mass star but since there is more mass, there is more gravitational energy to further the process through Iron. As Helium runs out in the core, it collapses until the outward pressure of the fusion of Carbon can withstand the inward force of gravity. Then the star's core collapses more and more as the heavier elements are fused.
More energy provided by the force of gravity on the core is needed to burn heavier and heavier elements until Iron is reached. At this point, there is not enough energy to fuse Iron. Massive stars such as these have life spans of millions to just a couple billion years unlike that of solar mass and smaller stars which have life spans of tens of billions of years.
For solar mass stars, the core will produce a number of helium flashes as it fuses through its remaining fuel. At some point, these helium flashes increase in intensity and will push off the outer layers of the star's atmosphere into space creating a "Planetary Nebula".
This name is a misnomer due to astronomers thinking these were distant planets before they were found to be nebula created by dying stars. There is nothing left over except for the dense hot core of the star that has ceased its fusion processes.
This leftover core is called a White Dwarf. As the large mass star fuses through the slew of elements ending at Iron, the core runs out of energy due to Iron needing energy to fuse it instead of being able to release energy when fused. When the core stops fusing at Iron, it collapses due to the loss of outward pressure and becomes overwhelmed with the inward force of gravity.
The very fast collapse of the core causes the outer layers to collapse also, but these outer layers hit the core of the star and bounce off with immense force. Energy is release in the form of neutrinos, light, and heat as the outer layers of the star are blown outward from the core.
Depending on the size of the initial star and how much material was left over, the core collapses into a Neutron Star or a Black Hole. White dwarfs are the left over cores of dead solar mass stars. They are comprised mostly of atoms of oxygen and carbon created by the fusion of hydrogen and helium in the stars.
This heat is from the left over heat of the fusion processes in the old core. There is no fusion process inside the leftover core. The size of a white dwarf is approximately the same size as the earth with about ,x the gravity and ,x the density if the radius is similar to Earth. There is a limit to the mass 1. Neutron stars are the left overs of stars with initial masses estimated to be times the mass of the sun. When the star finally supernovas, the left over mass in the core needs to be above the 1.
Instead of being a ball of left over carbon or oxygen atoms, the electrons interact with the protons and form neutrons through the process of electron capture. This in turn creates a massive ball of neutrons with a radius of about 10 Km 6.
When the core collapses, the angular velocity of the rotation of the star is conserved in the core.
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