--------------------- #1501 - Redshifting Back In Time
- Since 1676 astronomers have known that light travels at a finite speed. Using the moons of Jupiter as a pendulum clock, astronomers measured the difference in time for the moons to pass Jupiter’s horizon at six month intervals of the year. In six months the Earth orbits at a point closest to Jupiter to a point furthest from Jupiter. That distance being the diameter of Earth’s orbit around the Sun. The time difference measured divided by that distance calculated the speed of light.
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- 336 years later our measurements put the speed of light at 186,282 miles per second.
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----------------------- 670,633,500 miles per hour
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---------------------- 5,880,000,000,000 miles per year
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- 5.88 trillion miles is the distance light travels in one year.
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- If astronomers observe a galaxy 1 million lightyears away, they are looking at that galaxy as it was 1 million years ago. That is how long it took for the galaxy’s light to reach us.
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- Through these observations astronomers have learned that the Universe in the past appeared much different than the Universe we see today.
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- In the beginning the Universe was only primordial gas, hydrogen and helium. It was only after the first stars formed out of this gas that nuclear fusion created the heavier elements. The first stars were giants, 300 to 400 Solar Mass. Our Sun is 1 Solar Mass. These giant stars had short lives due to their immense gravity and rapid fusion of their hydrogen and helium fuel. When they ran out of fuel they collapsed and exploded into a supernova with immense heat and pressure that fused the lighter elements into heavier elements. Stars that formed later out of the interstellar medium created from the first stars contained these heavier elements.
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- Each element is different. The light spectrum from stars contains absorption lines that are fingerprints for each element. Each absorption line pattern represents specific wavelengths of energy absorbed by an electron as it jumps to higher excited orbits. Every element has its own unique set of electrons in orbit. Elements can be identified in the light spectrum using these “fingerprints” of absorption lines.
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- In 1950 Quasars were first discovered. “Qausi-Stellar Objects” had spectral absorption and emission lines that were unlike any known elements found on Earth. At first they were thought to be newly discovered elements. It was not until 1960 that Caltech in Pasadena discovered that these fingerprints were really known elements that had their wavelengths redshifted to longer wavelengths due to the expanding space.
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- By 1980 Quasars were understood to be the central regions of galaxies that contained massive Blackholes. Billion Solar Mass Blackholes consume vast quantities of gas. The gas forms in an accretion disk orbiting just outside the Event Horizon. The rotating gas heats up and emits intense energy that astronomers see as a point source of light from a Quasar.
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- The earliest Quasar discovered so far has a redshift of 7.085 times, which means it exists just 770,000,000 years after the Big Bang. This tells us that galaxies first formed before this time.
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- Astronomers started using the fingerprints of neutral hydrogen to look even further back in time. Neutral hydrogen emits photons at a wavelength of 21 centimeters. The redshifts for these longer wavelengths require telescopes using low-frequency radio waves. Using this technique the most distant galaxy was found at 480,000,000 years after the Big Bang.
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- The table that follows lists some of these most distant discoveries:
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-------------------------------------------------------- Redshift ----- Years after BB
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--------- 1960 ------------- Galaxy --------------- 0.461 --------- 8.9 billion
--------- 1965 ------------- Quasar --------------- 2.018 --------- 3.3 billion
--------- 1974 ------------- Quasar --------------- 3.53------------ 1.8 billion
--------- 1987 ------------- Quasar --------------- 4.01 ---------- 1.6 billion
--------- 1997 ------------- Galaxy --------------- 4.92 ----------- 1.2 billion
--------- 1998 ------------- Supernova ----------- 0.83 ----------- 6.7billion
--------- 2001 ------------- Quasar --------------- 6.28 ----------- 0.9 billion
--------- 2009 ------------- Supernova ---------- 2.357 ---------- 2.8 billion
--------- 2010 ------------- Galaxy --------------- 8.56 ----------- 0.6billion
--------- 2011 ------------- Quasar --------------- 7.085 ---------- 0.77 billion
--------- 2011 ------------- Galaxy Cluster ------ 2.07 ---------- 3.2 billion
--------- 2011 ------------- Gamma Ray Burst -- 9.4 ----------- 0.52 billion
--------- 2011 ------------- Galaxy ---------------- 10 ------------ 0.48 billion
--------- 2012 ------------- Supernova Type 1a -- 1.55 ---------- 4.2 billion
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- From the table Gamma Ray Bursts have been discovered occurring 520,000,000 years after the Big Bang.
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- A Galaxy Cluster existed 3,200,000,000 years after.
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- The most distant Quasar at a redshift of 7 at 770,000,000 years after.
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- The most distant galaxy at a redshift of 10 at 480,000,000 years after.
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- Of course the greatest redshift object is the CMB at 1,100 redshift and 380,000 after the Big Bang. This object is the Cosmic Microwave Background Radiation that was emitted in the infrared wavelengths when hydrogen atoms first lost ionization and became neutral allowing the photons to escape. Today we detect their redshifted light in the microwave end of the electromagnetic spectrum.
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- To see backwards in time even further astronomers need to detect even longer wavelengths. This requires even bigger telescopes. A telescope planned for Chile is 24.5 meters in diameter. One planned for Mauna Kea, Hawaii is 30 meters. A European telescope also planned for Chile is 39.3 meters.
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- It is race to ever higher redshifts to see farther back in time. Only in astronomy do you get to do this sort of thing. An announcement will be made shortly, stay tuned.
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(1) More about redshifts #925 Hydrogen Radio Signal.
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(2) #835 The Redshift Explained.
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