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Stars (Magnitude (Apparent Magnitude \(m\) How bright a star appears to…

- - - - Red Giant
        Once all the hydrogen runs out in the core, the star starts to collapse once more. The core and the outer layers become hotter. Eventually a shell of hydrogen around the core becomes hot enough for hydrogen to fuse to helium. This prevents the collapse of the outer layers.
        The core continues to collapse, heating as the matter falls inwards, heating the shell and increasing the rate of fusion and outwards radiation pressure. This causes the outer layers to be pushed outwards, cooling the outer layers (appears redder), and causing the star to become brighter as the total power output increases.
        Eventually the core becomes hot enough for helium to fuse into carbon and oxygen, and so fusion starts in the core. This heats the shell more, stops further collapse, and increases the size and luminosity of the star further. The dual fusion causes the star to become unstable, and the star starts to pulsate in brightness as the fusion comes in and out of phase
        
        Less than 8 solar masses
        
        White Dwarf
        Carbon and oxygen run out in the core and the core collapses. the shell becomes hot enough for helium to fuse into carbon and oxygen. The core continues to collapse heating the shell lots. This increases the outwards radiation pressure, and the outer layers of the start start to become ejected to form a planetary nebula. The core collapse continues until the electron degeneracy pressure within the plasma resists the inwards gravitational pressure. A small hot white dwarf star is produced which will cool over time. About the same size as the Earth.
        
        More than 8 solar masses
        
        Red Supergiant
        Once helium runs out in the core the star collapses again, and the shell becomes hot enough for helium to fuse, another shell above becomes hot enough for hydrogen to fuse, and the core becomes hot enough for carbon to oxygen to fuse. This repeats, with star layering at each stage moving outwards. At each stage the radiation pressure becomes larger, the layers are pushed out further, the star becomes brighter, the surface temperature drops (star appears redder) and the star becomes larger.
        This continues up to when Iron-56 runs out, as fusing iron-56 will not release energy. At this point the core collapses very quickly, and makes it past the electron degeneracy pressure. Electrons and protons are made to combine to form neutrons, releasing huge numbers of neutrinos. These neutrinos have a large kinetic energy, due to the loss in energy due to the core collapse. The neutrinos transfer energy and momentum to the inflowing outer layers and cause an ejection. A super nova is created.
        
        Core has less than 3 solar masses
        
        The SNF can resist the collapsing neutrons. The core is compressed to sub-nuclear densities, but the core recoils, and after the supernova has occurred, a neutron star will be left.
        
        Neutron Star
        Neutron stars are made entirely from neutrons, and so are very dense (nuclear density) (30km in diameter)
        
        During the collapse neutron stars can gain a large angular velocity, and so can be spinning very quickly.
        
        They can also have strong magnetic fields around them, causing radio waves to be ejected in jets along the poles of the field. These jets will rotate about the axis of rotation, and so if one or more jets passes through our line of sight we observe a neutron star as a pulsar: A periodic, intense radio signal.
        
        Core has more than 3 solar masses
        
        The SNF cannot resist the collapse of the core, and so the core collapses well past nuclear densities, and eventually past the Schwarzchild radius, becoming a black hole.
        
        Black Hole
        Object with a horizon, past which the escape velocity to escape the object's gravitational field is greater than the speed of light
        
        Supernova
        A brief and rapid decrease in absolute magnitude
        
        The energy released in a supernova is about the same as the total energy released by the sun over it's entire lifetime
        
        Gamma Ray Bursts
        When a black hole is formed, parallel jets of gamma rays can be ejected for times of minutes up to hours.