Download Rachel Henning

Rachel Henning
Professor Jacak
11/2/06
Homework #8
1. What is the expected fate of our sun? What happens to stars that are much more
massive than our sun? In about 5 billion years, the hydrogen in the center of the
Sun will start to run out. The helium will get squeezed. This will speed up the
hydrogen burning. Our star will slowly puff into a red giant, which is a star that
has exhausted it hydrogen and is burning helium fuel. It will eat all of the inner
planets, even the Earth. Then the sun would burn into carbon, but it is not big
enough so it will probably end up being a white dwarf.
2. What are the two possible outcomes following a supernova explosion? For stars
with higher masses than the Sun (up to about 40 times greater), the outer layers of
the star may be thrown off with much more force. This is a supernova. This type
of star collapses down to a very compact size. This is what is called a "neutron
star". The other outcome can be a black hole. Explain what determines which
ultimate fate awaits an exploding star. The size of the star helps to determine and
also deleptonization.
3. List two kinds of reactions that can be used to create heavy elements in terrestrial
experiments. Rapid process and Slow process.
4. What material are stars formed from? What force causes star formation? A nebula
is formed first, this is a cloud of dust and gas made from hydrogen and helium,
after equilibrium is achieved and the temperature increases a prostar is formed.
After that, it is either a brown dwarf or nuclear fusion begins.
5. When a neutron star is formed, what happens to all of the electrons in the star?
When it reaches the threshold of energy necessary to force the combining of
electrons and protons to form neutrons, the electron degeneracy limit has been
passed and the collapse continues until it is stopped by neutron degeneracy. At
this point it appears that the collapse will stop for stars with mass less than two or
three solar masses, and the resulting collection of neutrons is called a neutron star.
The periodic emitters called pulsars are thought to be neutron stars.
6. Name 5 stages that the universe went through following the Big Bang. Explain
what each one is and how old the universe was when it happened.
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During the first 10-43 seconds the four fundamental forces are unified (although no
complete physical description of this era yet exists). Temperature 1032 Kelvin. 1043
seconds defines the time when gravity splits from the other forces (weak, strong
and Electro-Magnetic).
Up to 10-35 seconds, quarks and anti-quarks dominate the Universe. The strong
force separates from the weak and electromagnetic forces. Temperature drops to
1027 Kelvin. At 10-12 seconds the four forces become distinct.
At 0.01 seconds, electrons and positrons form as the temperature drops to 1011
Kelvin. After 1 second, the Universe becomes transparent to neutrinos, which
from now on hardly interact further with matter.
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At three minutes after the big bang, the temperature has reached 109 K, protons
and neutrons combine to form what will become the nuclei of elements (mostly H
and He). After 300,000 years the temperature has dropped to 3000 K and the
electrons are captured by nuclei to form neutral atoms. The Universe becomes
transparent to light (photons stop interacting with free electrons) resulting in the
formation of the Cosmic Background Radiation.
After 1 billion years, the temperature is 20 K and galaxies and stars have begun to
form via gravitational contraction of over-densities in the initial Universe. A few
billion years our Galaxy forms, at about 10 billion years after the Big Bang the
Sun and Earth form. After 15 billion years we reach the present and a background
temperature of about 3 K.