WHITE DWARFS�&�PLANETARY NEBULAE
WHITE DWARF STARS
A White Dwarf is composed of Carbon atoms, free electrons, and a few other elements.
It is what remains of the core of a star between ~0.8 and ~8 solar masses when He fusion stops.
WHITE DWARF STARS
Electron Degeneracy Pressure keeps a white dwarf from collapsing further.��The electrons in the carbon atoms repel each other by electrostatic force.
This and quantum mechanics effects cause the electrons to repel each other very strongly; enough to keep the star’s core from collapsing.
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WHITE DWARF STARS
A white dwarf is about the size of the Earth, but has ½ the mass of the Sun.
It is very dense. 1cm3 has a mass of a metric ton (1,000kg).
Gravity is about 1,000 times greater than Earth.
White Dwarf Stuff
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WHITE DWARF STARS
Temperature is about 100,000°C.
At this temperature it gives off large amounts of radiation, mostly high energy ultraviolet light.
PLANETARY NEBUAE
The outer layers that were thrown off during the end of the star’s life glow because of the radiation emitted from the white dwarf.
This is called a planetary nebula.
PLANETARY NEBUAE
Charles Messier created a catalog of bright objects that he thought were comets.
Many of these turned out to be planetary nebulae.
PLANETARY NEBUAE
PLANETARY NEBUAE
When viewed in different wavelengths planetary nebulae have different shapes for a variety of reasons;
e.g. a binary star system may elongate the nebula.
e.g. planets orbiting within the nebula may distort it very randomly.
PLANETARY NEBUAE
Different elements in the nebula cause them to have many different colors.
A planetary nebula may only last for about 1,000 years before is dissipates entirely.
Type 1A Supernovae
Most stars are binary; a system of two (or more) stars orbiting each other. These were likely formed at the same time from the same gas cloud and have been gravitationally locked since they were born.
Type 1A Supernovae
If one of these becomes a white dwarf star it may slowly pull H and He gas from its larger companion. This gas builds up around the white dwarf.
Type 1A Supernovae
Using the theories of relativity and quantum mechanics, Subrahmanyan Chandrasekhar calculated the maximum mass a white dwarf could be under these conditions and remain stable.
Type 1A Supernovae
1.4 solar masses is known as the Chandrasekhar limit. When a white dwarf star exceeds this limit by accumulating mass on its surface, all of its mass fuses nearly instantly.
Type 1A Supernovae
This release of energy is known as a Type 1A supernova. In less than a second it produces more energy than our Sun produces in 11 billion years.
Type 1A Supernovae
Because Type 1A supernovae are produced just as the white dwarf reaches 1.4 solar masses, they are all the same brightness (within~1%).
Type 1A Supernovae
Since they are the same brightness no matter where they happen and because they are bright enough to be seen across the universe, we have used them to measure the distances to other galaxies and the size of the universe.
Type 1A Supernovae
Type 1A Supernovae