- 4047 - HR DIAGRAM - plots the color of stars. One of the most famous diagrams and most useful in astronomy is the Hertzsprung -Russell Diagram. ( HR Diagram ). It was created from a simple idea. Plot the characteristics of stars in brightness versus their color. Brightness is a measure of luminosity, or intensity of radiation. Color is the surface temperature of the star.
------------- 4047 - HR DIAGRAM - plots the color of stars.
- Published in 1908 and
in 1911 the HR Diagram reveals the lifetime of stars. Each star has a predetermined lifetime and
evolution depending on its mass. The
diagram successfully grouped the stars according to their stage in life.
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- The plot displayed a
distinct diagonal line of dots (stars ) from the upper right (hot and blue
stars ) to the lower left ( cold and red
stars ). The diagram plotted descending
temperatures on the x-axis from 31,000 Kelvin (blue) to 2,200 Kelvin (red) And, plotted ascending brightness on the
y-axis from 1/100,000 Sun’s brightness to 100,000 Sun’s brightness.
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- The diagonal line
became known as the “ Main Sequence” line for star evolution. All stars generate electromagnetic energy,
the light spectrum from radio waves to
Gamma Rays. All stars do this be
converting Hydrogen into Helium in nuclear fusion at the core of the star.
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- The more massive the
star, the stronger the gravity, and the hotter the core, the faster the nuclear
reaction, the brighter the star, and the shorter its lifetime.
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- There are some groups
of stars that are off this Main Sequence diagonal line. The stars in the upper right corner are stars
that are cooler yet brighter than our Sun.
Our Sun is on the Main Sequence line and about in the middle at 6000
Kelvin. How can a cooler star be
brighter, 100 to 1,000 times brighter than our Sun?
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- Answer: These stars are enormous. Supergiants.
They are so big they produce less light for every square inch of their
surface.
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- There is another group
of stars off the diagonal line in the lower left corner that are dimmer and
hotter. These stars are tiny. The are called White Dwarfs. White hot and tiny. This is what our Sun will be in 5,000,000,000
years from now.
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- The Pleiades Cluster is
a group of stars that include bright blue stars. The cluster is in the Constellation Taurus
the Bull and is often called the “ Seven Sisters”. In Japan it is called “ Subaru”.
- The Hyades Cluster ,
also in the Constellation Taurus, is missing blue stars. Therefore, the Hyades Cluster must be older
stars. The bright blue stars in the
Hyades Cluster have all exploded as supernovae and died off.
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- The bottom-right of the
diagonal line are the dimmest, reddest, and least massive stars. the smallest is about 8% the mass of the
Sun. These are called Brown Dwarfs and
are too lightweight to sustain nuclear fusion.
They are 1/100,000 the Sun’s brightness and 3,000 Kelvin.
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- The upper-left of the
diagonal line are the brightest, hottest and most massive stars. Up to 100,000 the Sun’s brightness and 30,000
Kelvin. The bright stars are the rarest
because they do not live long, maybe only a few million years before they
explode in a supernova. The largest star
might be 150 times the Sun’s mass.
However, some astronomers claim they have found stars up to 320 times
the Sun’s mass. The very first stars in
the Universe may have been this massive.
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- Early evolution stars
were made of only Hydrogen and Helium.
Second and third generation stars contain Carbon and Oxygen that were
created in the earlier supernovae explosions.
Carbon and Oxygen emit infrared light (heat energy). This allows them to cool faster.
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- Today’s stars are
second and third generation stars and likely not as massive , only 100
times the Sun’s mass. Any star that is
greater than 8 Solar Mass will end its life
exploding as a supernova. Smaller stars like our Sun will die as
Planetary Nebulae and then White Dwarfs.
They will not explode as supernovae.
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- In our Milky Way
Galaxy, out to 20,000 lightyears away, there are only a few stars that might
explode as supernovae. 1604 was the year
of the last one recorded. It is now know
as Kepler’s Supernova. Betelgeuse and
Antares are the nearest and brightest stars likely to explode next. They are 640 and 550 lightyears away
respectively. When they explode they
will be as bright as the Full Moon in the sky, but, they are far enough away
that the explosion itself will not reach us.
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- The 1987 Supernova
explosion occurred in our sister galaxy, the Large Megellanic Cloud
galaxy, But, it was not a red super
giant star, it was a blue star that went supernova. Two stars that are similar in this way in our
galaxy are Deneb and Rigel.
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- Other types of
supernovae come from binary stars. One
star steals mass from its orbiting companion star until it reaches 1.4 Solar
Mass and explodes. Unfortunatly these
exploding White Dwarfs are so dim before they go supernova it is hard to predict
how many are out there as binary stars.
Almost 60% of all stars are binaries.
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- Can you believe all
this was learned from a simple diagram invented in 1908. There is still more to learn, an announcement
will be made shortly, stay tuned.
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-
June 9, 2023 HR DIAGRAM
- plots the color of stars 1283
4047
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Friday, June 9, 2023
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