- 4095 - STARS
- determining their ages? How old are the stars? Well, they are all different ages from just
born to just dying at 13 billion years old.
Our Sun is 4.6 billion years old and will not die until it is 10 billion
years old.
--------------------------- 4095 - STARS - determining their ages?
- How do we know how old
our Sun is?
-
- 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.)
-
- The Sun is half way
through its lifetime as it is expected to live for 10 billion years.
-
- How do we know how long
the Sun will live?
-
- 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.
-
- 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.
-
----------------------
4,567,000,000 years old is our Sun today
-
---------------------- 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.
-
-------------------- 6.2
billion years old all water will boil away including all life , even bacteria.
-
-------------------- 10
billion years old the Sun will have burned all its fuel and will begin
transforming into a Red Giant Star.
-
------------------- 12.2
billion years old the Red Giant Sun will
expand to where it will swallow up Mercury, Venus, and Earth.
-
-------------------- 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.
-
- Our Sun is a medium size
star, one Solar Mass. Every star’s
lifetime is different depending on how big it is.
-
- 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.
-
- 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.
-
- 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.
-
- Planets that are 1
billion years old could have microbe life.
-
- Planets that are 3
billion years old could have primitive life in its oceans and on its land.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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”.?
-
- 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.
-
- 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.
-
-
July 18, 2023 4095
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Tuesday, July 18, 2023 ---------------------------------
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