Now let us look at things from a different angle. What if you knew that
a certain supernova is located about 3 kiloparsecs from Earth. When
astronomers look at the remnant with their telescopes, they measure it to
be 8 arc minutes (480 arc seconds) in diameter. What is the radius of the
remnant in kilometers? Scientists have also measured the expansion
velocity to be 4,800 km/sec. In what year did the supernova occur? Perhaps
you can look up in a library, or on the World Wide Web, information about
supernovae observed to occur in that year and find the common name of this
supernova remnant. Need a hint?... Johannes Kepler was a famous
A Teaspoon of Starstuff
Subrahmanyan Chandrasekhar (1910-1995) was born in Lahore, a
part of India that is now in Pakistan. He won a Government of India
scholarship and entered Cambridge University in England to work on his
doctorate. As he sailed from India to England, he thought a lot about the
death of stars. Using Einsteinís theory of relativity, he calculated that
stars of a certain mass should not become white dwarfs when they died; he
believed that they should keep on collapsing. He put aside this work,
earned his doctorate in 1934, and only later actively returned to his
theory. He calculated that stars with more than 1.44 times the mass of the
Sun (now known as the Chandrasekhar limit) would not become white dwarfs,
but would be crushed by their own gravity into either a neutron star or a
black hole. His work was viciously criticized by Sir Arthur Eddington,
then the leading authority on stellar evolution and someone greatly
admired by Chandrasekhar. His standing diminished by Eddington's attacks,
he came to the United States and was hired to teach at the University of
Chicago. There he continued his research, which produced significant
advances in the field of energy transfer in stellar atmospheres.
Eventually, his calculations about white dwarfs were proven correct. With
the recognition of the Chandrasekhar limit, the theoretical foundation for
understanding the lives of stars was complete. He won the Nobel Prize in
physics in 1983.
There are indeed distinct differences in the states of matter contained
in main sequence stars, white dwarfs, and neutron stars. The following
exercise will help you to understand just how different they are!
Look at the following chart and use the information you find there to
calculate how much a teaspoonful of each object would weigh here on Earth.
Assume that a teaspoon will hold about 5 cubic-centimeters of
|Object||Mass (grams)||Radius (cm)|
|Sun||2 x 10 33||7 x 1010|
|White Dwarf||1 x 10 33||5 x 108|
|Neutron Star||2 x 10 33||9 x 10 5|
Can you now relate these numbers to materials you know here on
Earth? How much does a teaspoon of water weigh? Or air? Or iron?
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