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---------------------1896 - Dark Energy and the expansion of the Universe.
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- Astronomers are convinced the Universe is expanding. And, it is expanding at an accelerating rate. In the last few decades technology has advanced so fast, astronomers are able to create a 3-D map of this expansion and the form it takes. It appears more like a spider web with filaments connecting nodes separated by voids but growing bigger.
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- Three primary measurement methods are being used:
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- (1) The Hubble Telescope observing Type 1a supernovae explosions.
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- (2) The Planck Satellite measurements on the Cosmic Microwave Background radiation.
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- (3) The Baryon Oscillation Spectroscopic Survey measuring pressure waves in the spacing of nodes and voids between galaxy clusters.
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- All three methods peg the expansion rate at about 150,000 miles per hour per mega parsec. A mega parsec is 3.3 million lightyears distance. This equates to 45,500 miles per hour per million light years. All three methods have results within 8% of each other. But, 8% leaves room for new discoveries. What can explain these differences?
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- Here are the results of each method of measurement:
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- (1) Type 1a supernovae are explosions of a White Dwarf Star that accumulates mass to reach 1.4 Solar Mass. This limit of gravitational pressure collapses electrons into their nuclei creating the recoil in a “ standard candle” supernova explosion.
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- These measurements get the expansion rate at 49,485 miles per hour per million lightyears distance. The measurement error is calculated to be + - 2.4%
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- (2) The Planck Satellite measurements get the expansion rate at 45,417 miles per our per million lightyears. This measurement error is +- 1%.
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- (3) The BOSS measurements reported the same result as Planck’s except the measurement error a +-1/5%. The expansion rate of 45,417 miles per hour per million lightyears. BOSS got this studying the patterns in clustering of 1,200,000 galaxies.
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- The difference is 4,068 miles per hour.
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- An 8% difference in different measurements of the same acceleration rate.
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- Each method is trying to refine the measurements and calculations to reduce measurement error.
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- (1) The Hubble Telescope is measuring objects of “ known” brightness, called Intrinsic Brightness. They calculate distances by measuring dimness and by measuring the shift in frequency , the spread of wavelength, traveling through expanding space. Besides Type 1a supernovae, Cepheid Variable Stars are also used because their pulsation rates can be correlated to their Intrinsic Brightness.
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- The Hubble Telescope measurements are working to refine their results by measuring two other types of stars, RR Lyrae Variable Stars and Red Giant Stars.
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- These particular type stars are identified in a galaxy where the distance is accurately known through other methods. Then, calculate the Intrinsic Brightness. “r “ is the distance.
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---------------------- Measured Brightness = Intrinsic Brightness / (4 * pi * r^2)
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- (4 * pi * r^2) is the surface area of a sphere of the expanding light radiation bubble.
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- When the same type of stars are identified in the most distant galaxy the Intrinsic Brightness is used to calculate the distance. The goal is to reduce the measurement errors to less than 1%.
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- The Hubble Telescope is also beginning to use Gravitational Lensing to image galaxies that were previously too dim to see. A cluster of galaxies, 100 times more massive than our Milky Way Galaxy can bend the light beams from the much more distant galaxies behind them. The focused beams act as a “magnifying glass“.
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- (2) The Planck measurements were made of the slightest temperature variations of the Cosmic Microwave Background radiation. They are extending these measurements beyond just temperature to the ‘polarization” of this radiation of the ancient light that originated 380,000 years after the Big Bang.
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- (3) Baryonic Acoustic Oscillations are sound waves that have stretched into today’s distribution of galaxies and voids. The Cosmic Microwave Background contains the same pressure waves that originated at that same time after the Big Bang. The pressure wave changes that have occurred over the last 13.4 billion years is a measure of how Normal / Dark Matter and Dark Energy have competed in governing the rate of expansion.
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- In the early Universe the mass was concentrated and gravity could actually slow down the rate of expansion. This lasted for the first 7 billion years. By then the mass had spread out so much gravity’s influence dissipated. The repulsive force of Dark Energy took over dominance and the Universe has been accelerating its rate of expansion ever since.
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- Astronomers are trying to learn what causes the vacuum of space to have a repulsive force? Is this force every where the save? Does this repulsive force change over time? Called a mysterious Dark Energy , it could be an evolving energy field and not just a constant pressure?
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- 8% is not a big difference in measurement results, but, astronomers are convinced it points to something missing.
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- Theories have proposed a new type of particle, a new type of neutrino that may be affecting these measurements.
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- Put together these measurements are creating a 3-D map or the Observable Universe. The picture is one of galaxy strings like filaments connecting galaxy cluster, called nodes. The spaces between are giant voids, nearly empty space containing only a few atoms per cubic meter and no galaxies.
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- This spider web tapestry is very similar to the neurons and nodes in the human brain. These astronomy reviews are designed to stretch your brain. Once stretched it will not return to its previous size. Enjoy!
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----- 707-536-3272 ---------------- Thursday, August 4, 2016 -----
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