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- How do the stars shine? How does the Sun produce energy and how long will it last?
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-The stars get their energy from the fusion of four hydrogen atoms to make a single helium atom.
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- Hydrogen is the simplest element consisting of one proton and one electron. The star starts out as a gas ball with gravity squeezing it into a denser and denser, a hotter and hotter, a smaller and smaller sphere until it becomes dense enough and hot enough at its center to causes a fusion reaction, a nuclear reaction.
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- The reaction creates a radiation pressure outward to balance the gravitational push inward. The radiation pressure at the center must be just right to hold up the weight of all the layers of plasma up to the surface of the star.
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- The amount of energy produced by our Sun is 3.85 * 10^26 watts per second. The fusion process is the conversion of mass to energy according to E = mc^2.
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----------------------- Energy = mass * ( speed of light )^2
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---------------------- Energy = mass * 90,000,000,000,000,000 joules
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- When two hydrogen atoms fuse to form one helium atom the mass of the helium atom is slightly less than the mass of the two hydrogen atoms. The small difference in mass is what is converted directly into energy.
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- The density and temperature at the core of the Sun needed to make fusion happen is density 150 times that of the density of water, the temperature is 15,000,000 Kelvin. This area where fusion occurs is only 0.1% of the Sun’s volume.
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- The fusion process begins with 2 hydrogen nuclei ( 2 protons ) , one proton turns into a neutron which releases an electron , a positron ( anti-electron) , a neutrino, and Gamma Rays. The proton + neutron is called Deuterium. Next, a hydrogen nuclei fuses with the
Deuterium to create helium-3 ( 2 protons and a neutron ), plus more Gamma Rays. The last step 2 helium-3 nuclei fuse together to form helium-4 ( 2 protons and 2 neutrons) plus 2 hydrogen atoms to continue the chain reaction for additional fusion to continue.
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- The electron and positron collide and annihilate each other into pure energy, Gamma Rays. The neutrinos is a neutral particle with very little mass. It escapes the surface of the Sun near instantaneously without interacting with any other particles.
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- In summary 4 hydrogen nuclei have fused to form one helium nuclei and Gamma Ray radiation. This radiation is what makes stars shine.
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- Gamma Ray photons do not immediately exit the surface of the Sun. In fact, the photons bounce between other charged particles to such an extent it takes up to 100,000 years for a photon to travel from the core to escape the surface.
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- Near the surface the convection occurs causing hot gases to bubble to the surface and radiate at 6,000 Kelvin, which is the surface temperature of the Sun.
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- We already mentioned that the Sun is radiating 3.85*10^26 watts of energy each second. How long can this go on before the Sun runs out of hydrogen fuel?
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- Converting 4 hydrogen to 1 helium results in a loss of mass to radiation. The hydrogen nuclei is 1.6726*10^-27 kilograms. Four hydrogen nuclei are 6.6904 * 10^-27 kilograms A helium nuclei is 6.6465*10^-27 kilograms. The difference is 0.0438*10^-27 kilograms. From E=mc^2 this small mass converts to Gamma Ray energy.
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-------------- E = 4.39*10^-29 kilograms * (3*10^8 m/sec^2) = 3.95*10^-12 joules
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- The number of hydrogen nuclei in a gram converted to helium releases 6*10^11 joules of energy. In truth the Sun converts 600 billion kilograms of hydrogen into helium every second transforming 4 billion tons of matter into Gamma Ray radiation every second.
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- Only about 10% of the Sun’s mass at the core will remain hot enough and dense enough to sustain fusion reactions.
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------------ The mass of the Sun is 2 *10^30 kilograms
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------------- 10% is 2 * 10^29 kilograms
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------------- 600 kilograms / second / 3.16 * 10^7 seconds per year =
------------ 1.9 *10^19 kilograms per year
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-------------- 2*10^29 kilograms / 1.9*10^19 kilograms per year =
----------- 10 8*10^9 years.
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- The Sun will sustain fusion for 10 billion years. It has already done so for 4.6 billion years so it has another 5.4 billion years to go. The Sun has not quite consumed 1/2 of its hydrogen fuel to date.
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- Here is a chart of the mass of the star and its expected lifetime. 1.0 Solar Mass is our Sun.
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---------------------- Solar Mass ------------ Solar Luminosity ------ Lifetime
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------------------------- 40 ----------------------500,000 ------------- 800,000 years.
------------------------- 6.5 ----------------------800 --------------- 81,000,000 years
------------------------- 2.1 ----------------------20 -------------- 1,050,000,000 years
------------------------- 1.3 ----------------------2.5 ---------------- 5.2 billion years
------------------------- 1.0 ------- SUN -------1.0 ---- SUN ---- 10 billion years
------------------------- 0.93 ------------------- 0.79 --------------- 12 billion years
------------------------- 0.69 --------------------0.16 --------------- 43 billion years
------------------------- 0.21 --------------------0.0079 ------------ 270 billion years
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- All the elements in the Periodic Table of Elements except hydrogen, helium, and deuterium were made in the fusion process of stars and in the supernovae explosions at the end of the star’s life. The three or four lightest elements were created in the Big Bang. All the heavier elements in the core of stars and the explosions of stars.
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- We have to wait for a long time for stars to explode but when this happens the results are amazing. Everything we see, everything we are, is made of about 100 elements. Each element built up from the element hydrogen ( one proton and one electron) with one additional proton in the nucleus and one additional electron in orbit around the nucleus. This worked up to 92 natural elements and 26 synthetic elements.
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- The Periodic Table has 118 elements but 24 of them do not normally occur in nature. Physicists have created the heavier elements by smashing protons into nuclei until they stick. These heavy elements are short lived and quickly decay into lighter elements.
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- Isotopes of elements occur when the nuclei add neutrons, neutral particles, to the protons in the nucleus.
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- Medical imaging sues the artificially synthesized isotope “technetium”
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- Smoke detectors use the isotope “ americium”
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- Each different element has different chemical properties. Learning how an exploding star, or, a particle accelerator is used to create a new element: “ Berkelium” has 97 protons in the nucleus. A calcium nucleus with 20 protons is smashed into it and a new atom of a new element is created with 117 protons.
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- The new element 117 lasted only a few seconds before decaying back into lighter elements. One of the breakdown products was also new. It had 103 protons “lawrencium” with 163 neutrons. Lawrencium-266, this new isotope of “ lawrencium” lived for 11 hours before it decayed.
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- More powerful particle accelerators are under development. They are needed. Today’s accelerators are having limited success. Example: Element 113 was being bombarded for 553 days over a nine year period. This is a lot of energy used to make a single atom.
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- Neutrons and isotopes are essential to the mix because neutrons help the strong nuclear force hold protons together. Protons are positive charges that repel each other unless the Strong Nuclear Force can overpowers the repulsive electromagnetic force.
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- New accelerators are capable of accelerating Uranium-238 to half the speed of light , to 93,000 miles per second.
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- Somehow supernovae explosions have produced iron, gold , and silver. To date , science has not been able to figure out how this process works More knowledge is needed. Not only for particle physics and astronomy but also for medical cancer treatments, and for safe nuclear power plants.
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----- 707-536-3272 ---------------------- Thursday, March 26, 2015 -----
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