--------------------- #1499 - Using Supernovae to Measure Dark Energy.
- Astronomers find about one new supernova explosion each night. These are stars that explode at end-of-life when they run out of nuclear fuel, violently collapse, bounce off their core in a tremendous explosion back into space. These supernovae are from all sizes of stars and all distances of space.
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- Astronomers are looking for a particular type of supernova. Called Type 1a Supernova it is believed to be the explosion of a White Dwarf Star. Its core is almost entirely made of carbon and oxygen. It is about the size of the Earth in volume. The core is what is left behind after a star sheds its outer hydrogen/helium shell.
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- The theory is that all White Dwarf supernova occur in the same way. The White Dwarf dead star’s gravity accrues additional mass by siphoning off mass from a companion star. The companion could be a normal star ( main-sequence star), a Red Giant Star, or another White Dwarf Star. If the White Dwarf accumulates mass that reaches 140% the mass of our Sun an uncontrolled thermonuclear fusion explosion occurs. The explosion becomes 10,000,000,000 times brighter that our Sun.
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- At 1.4 Solar Mass the amount of gravity pressure inward is greater that the electron pressure of atoms outward. The atoms can not hold up. Electrons collapse into the nuclei creating neutrons. A fusion explosion occurs that is equivalent to 100,000,000,000,000 trillion hydrogen bombs. The explosion consumes all of the core’s carbon and oxygen fuel in seconds. The mass converts into energy. The amount of energy is calculated to be 10^36 watts. If true, that consistent wattage becomes a “standard candle” for astronomers.
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- If you know how bright a light source is and you measure how dim it becomes due to its distance away from you, you can calculate its distance based on that measured luminosity. ( See note 1 for the calculation).
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- Also, if astronomers measure the spectrum of the light they can measure how much redshift has occurred due to the speed the galaxy is moving away from us. Or, more accurately, how much the space has expanded between us and the galaxy containing the supernova.
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- If the wavelength of the peak color of the spectrum has gotten bigger, the wavelength shifts towards the red end of the spectrum, it indicates that the Universe has expanded during the journey, during the time it takes the light to reach us. The greater the expansion , the greater the redshift of wavelength, the greater the distance, the longer the time of light travel.
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- By measuring Type 1a Supernovae explosions over distances of 1 billion, 3 billion, and 5 billion light years the redshift tells how fast the Universe has expanded over those time periods.
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- If the expansion were constant and the Universe were empty the plot of the redshift with time would be a flat line. If the Universe were composed of 100% matter (gravity) and no Dark Energy of repulsion the plot would decay rapidly with greater redshifts and greater distances. A plot of actual measured supernovae data with a best fit line occurs if we assume 30% matter and 70% Dark Energy for the composition of the Universe.
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- To astronomers surprise the data also showed that the Universe was not only expanding with this ratio of mass to energy, it was accelerating in its expansion. The Universe continues to become less dense, more rarefied. Galaxies keep moving away from each other faster. Eventually astronomers will not see any galaxies outside our local group that is still held together with gravity. ( See Review #1500 “ The Infinite Universe”, to learn more thoughts on what comes next.)
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707-536-3272, Tuesday, October 16, 2012
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