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- How old are the stars?
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- Well, they are all different ages from just born to just dieing at 13 billion years old. Our Sun is 4.6 billion years old and will not die until it is 10 billion years old.
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- How do we know how old our Sun is?
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- Meteorites, that were asteroids that land on the surface of Earth, which were part of the accretion disk of dust and gas that formed the Sun and circled the Sun to create the planets, were analyzed using radioactive dating. Radioactive elements decay at a specific rate from a heavier element to a lighter element. By measuring the ratio of the two in a primitive meteorite we can calculate how long it has been decaying. The oldest meteorites are 4.6 billion years old. Therefore the Sun must be 4.6 billion years old. ( See Review # 1554 to learn about these asteroids formations in the early Solar System.)
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- The Sun is half way through its lifetime as it is expected to live for 10 billion years.
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- How do we know how long the Sun will live?
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- The Sun is powered by nuclear fusion. The center of the Sun, the core, is so dense, and so hot, the core reaches 27,000,000 F which is hot enough to cause a thermonuclear reaction of hydrogen nuclei. Hydrogen nuclei fuse into helium nuclei. Not all the matter of hydrogen ends up as matter of helium. Some of the matter gets converted to radiation energy according to E = mc^2. The radiation energy pushes outward from the core against the gravity that is pushing inwards toward the core. The two forces are in balance as long as the Sun does not run out of hydrogen fuel. The gravity is relentless.
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- The Sun is fusing 620,000,000 tons of hydrogen every second. That sounds like a lot but the Sun is very, very big. At this rate the Sun will have enough fuel to shine for 10 billion years.
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---------------------- 4,567,000,000 years old is our Sun today
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---------------------- 5,3 billion years old, just 700 million years from now, Earth will absorb all the carbon dioxide in the atmosphere and all the plants will die because they can no longer live on photosynthesis. Animals will go extinct too. That’s us.
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-------------------- 6.2 billion years old all water will boil away including all life , even bacteria.
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-------------------- 10 billion years old the Sun will have burned all its fuel and will begin transforming into a Red Giant Star.
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------------------- 12.2 billion years old the Red Giant Sun will expand to where it will swallow up Mercury, Venus, and Earth.
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-------------------- 12.4 billion years old and the Red Giant Sun will transform into a planetary nebula ejecting outer layers of gas into outer space and leaving behind a White Dwarf Star. The White Dwarf will cool down as a hot cinder. It will not be big enough to every start fusion again. It is a dead star. Bigger stars can end up as Neutron Stars or Blackholes but not our Sun.
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- Our Sun is a medium size star, one Solar Mass. Every star’s lifetime is different depending on how big it is.
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- Stars that are 10% to size of our Sun shine 1/1,000th as bright and will live 100 times longer, 1,000 billion years.
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- Stars that are 500,000 times bigger than our Sun shine so brightly that their lifetimes are 10,000 times shorter. Only a 1,000,000 years of lifetime before going supernova.
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- Our Milky Way Galaxy has 200,000,000,000 stars of all sizes and all ages. Planets have already been discovered orbiting over 1,000 of these stars. It is estimated that there must be 200,000,000,000 planets in the Milky Way Galaxy alone. These planets are the same age as their stars. If we know the age of the star we may be able to predict if there is life on its planets.
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- Planets that are 1 billion years old could have microbe life.
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- Planets that are 3 billion years old could have primitive life in its oceans and on its land.
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- Planets that are 4.6 billion years old could have intelligent life, like humans, or like orangutans. Or, smarter than humans. It all depends on the speed of evolution and the myriad of factors that affect it.
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- The stars in the range of 1 to 5 billion years old all look alike, like our Sun. We can not tell the age from the color, color is the surface temperature of the star. Young stars are red, they get blue-white as they get older then red again when they die. Medium life spans look like our Sun are all the same color. We need another way to tell age besides color, or surface temperature and size.
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- One discovery that helps us are Star Clusters. Clusters of thousands of stars that were all born at the same time. They all are different sizes. They all have the same composition. They all are the same distance away. They all have the same ages.
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- All stars have a different spin rate. Our Sun spins one rotation in 25 days. Younger stars spin faster and older stars spin slower. Maybe spin rates can correlate to the ages of these medium size stars.
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- The Kepler Space telescope that has been discovering these 1,000 planets by measuring precisely the brightness of stars and detecting the dimming of the star when the planet passes in front of the star. The Kepler Telescope stares at one spot in the sky measuring the brightness of 160,000 stars every 30 minutes. If a particular star dims a planet may be passing in front of it or a sunspot may be rotating around the surface. The orbits and periods are measured carefully to determine what exactly caused the star to dim. It could be a binary star with a Red Dwarf passing in front.
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- When further analysis determines the dimness is a sunspot the rotation period can be measured to get the spin rate of the star. If we focus on a Star Cluster where all the ages are the same we can determine what size stars have what rates of spin. Measuring spin rates can than be used to know the age of the orbiting planets.
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- Those planets with the ages 1 to 5 billion years deserve greater study. What is the temperature of these planets? Could there be liquid water. What is the composition of the atmosphere? Are we alone? Should we send a radio signal to say “Hello”?
Stay tuned and announcement will be made shortly.
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(1) The astronomers study star ages are in the field of Gyrochronolgy
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(2) See the Kepler Cluster Study for more information
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(3) To learn the surface temperature of a star from its color.: The emitted power from each square meter of the surface of a star is directly proportional to the forth power of the Temperature:
------------------------- Power = Constant * T Kelvin^4
------------------------- Constant = 5.7*10^-8 watts / (m^2*Kelvin^4)
------------------------ To find the total power multiply by the surface area of the star.
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(4) The color of the star is the peak wavelength of the energy-density function. The wavelength is indirectly proportional to Temperature.
---------------------- Wavelength at maximum = Constant / Temperature
----------------------- Wavelength = 2,900,000 nanometers * Kelvin / Kelvin
----------------------- w = 2,900,000 / T
---------------------- Max. wavelength for our Sun = 500 nanometers
---------------------- Max. frequency for our Sun = 600,000,000,000,000 cycles per second.
---------------------- w * f = c = 300,000,000 meters per second
---------------------- Max color is blue green, but the blue scatters out in our atmosphere and we see a yellow Sun.
---------------------- The full range of radiation wavelengths of our Sun ranges from 70 nanometers to 4,800 nanometers, from far ultraviolet to far infrared. The peak occurs at 500 nanometers of the blackbody energy-density curve. That is why the sky is blue and the Sun is yellow, and middle - aged. We have several million years yet to live before the Sun gets hotter and evaporates all the oceans.
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RSVP, please reply with a number to rate this review: #1- learned something new. #2 - Didn’t read it. #3- very interesting. #4- Send another review #___ from the index. #5- Keep em coming. #6- I forwarded copies to some friends. #7- Don‘t send me these anymore! #8- I am forwarding you some questions? Index is available with email upon request. Some reviews are at http://jdetrick.blogspot.com Please send feedback, corrections, or recommended improvements to: jamesdetrick@comcast.net. ---- “Jim Detrick” -- www.facebook.com, -- www.twitter.com, -- 707-536-3272 Monday, January 21, 2013
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