- 1701 - The Expanding Universe? The Universe’s expansion was slowing the first 5 billion years due to gravity. The last 5 billion years the Universe is expanding at an accelerating rate. Today it is expanding at 47,000 miles per hour for every 1 million lightyears of space.
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--------------------------- 1701 - The Expanding Universe? ?
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- When the Hubble Space Telescope looks back in time it can see how active star formation was occurring over billions of years.
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- The Conclusion: The peak in star formation occurred 5 billion years ago. Star formation has become consistently less active ever since.
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- To see back this far the Hubble camera has to take a very long time exposure lasting 72 hours. The focus remains on one spot in the sky. The diameter of the spot is the size of 10% that of a full moon.
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- Hubble began a second study, called “ CANDLES” that repeated these measurements for 600 hours over an area the size of a full moon ( ½ arc degree ). 250,000 galaxies are under study from this data collection.
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- Astronomers are seeing that the “ Red Galaxies “ are usually elliptical and featureless. These Red Galaxies stopped forming stars about 1 billion years ago. “ Blue Galaxies” tended to be flat disks with spiral arms possessing lots of cold gas and stars of different ages.
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- The oldest galaxies are found with a look-back time of 10 billion years . The Big Bang occurred with a look-back time of 13.7 billion years.
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- Astronomers are surprised to find Red Galaxies being already common only 3 billion years after the Big Bang.
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- Elliptical, Blue Galaxies found were only 30% the size of typical elliptical galaxies found today. Clearly elliptical galaxies have grown over time through mergers and collisions. Our Milky Way galaxy has devoured dozens of smaller, dwarf galaxies. The Milky Way and Andromeda Galaxy will devour each other 5 billion years from now.
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- 5 billion years ago was the peak of star formation and these galaxies were distorted and misshapen, clumpy, and irregular. Clearly our smooth disks and spiral armed galaxies have gained their shape over time.
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- The picture astronomers are putting together suggests that after the Big Bang the Universe was nearly a uniform sea of Dark Matter, and, hydrogen and helium gas, ordinary matter. As the Universe expanded uniformity gave way to denser regions of Dark Matter gravitationally causing cold gas to expand more slowly. Eventually these dense regions collapsed into smaller structures. The structures appeared as filaments interconnected to denser blobs of gas and Dark Matter. These blobs were the seeds of the formation of the galaxies.
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- The early galaxies formed from clumps weighing a billion Solar mass and rapidly formed stars. At the same time this process led to the rapid growth of super massive Blackholes. Galaxies 10 billion years ago were 10% the mass of the Milky Way and were churning our stars at a rate 100 times faster than our galaxy today.
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- Because super massive stars burn so brightly they produce ultraviolet light in prodigious quantities. Neutral hydrogen gas can be ionized by absorbing ultraviolet light. The gas became free electrons and protons that caused the intergalactic medium to become ionized with charged particles.
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- Another discovery was made by taking time exposures 60 days apart. Subtracting one image from another revealed anything that changed. Supernovae explosions could be easily detected. Using their intrinsic brightness ratios to their apparent brightness the galaxy distances could be calculated.
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- The Result: Cosmic expansion was decelerating over the first 5 billion years. Expansion has been accelerating ever since. To get a 3-D picture of expanding space and competing contracting gravity forces 3 measurements were used. The telescope measures the position of the star in the sky. The spectroscope uses a prism to split the starlight in to its constituent colors. The spectroscope is used to measure the stars radial velocity. It also measures the star’s temperature, age and composition.
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- The telescope measures proper motion across the sky and parallax. Its resolution capability is analogous to measuring the size of a quarter 3 miles away. When all three measurements are taken together a star’s 3-D position in space can be calculated. ( GAIA spacecraft at Lagrangian orbit 900,000 altitude is doing this.)
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- These measurements are confirming that the Universe is expanding 47,000 miles per hour for every 1 million lightyears of space. The Sun is 93 million miles from the Earth. If Dark Energy alone was the expanding force that amount of space would expand 4.13 inches per year. Someone needs to double check my math. I don’t thing we would notice 4 inches a year. And , of course, gravity is the other force in the opposite direction. Angular momentum another force. What makes expanding space significant is the enormous distances between galaxies in the Universe. There is a whole lot of space out there to expand.
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- 3.16 *10^7 seconds per year.
- 5.88 * 10^12 miles per lightyear.
- 47,000 miles per hour is 827,000 inches per second
- Sun distance is 9.3*10^5 miles
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