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Stars & Nuclear Energy Guided Notes
(Taken from parts of Sections 10.4, 26.2, 26.3 in the book)
A star is a large, glowing ball of gas in space, which generates energy through nuclear fusion in its core. The closest star to Earth is the sun.
In space, dust & gas get pulled together by gravity. This is called a nebula.
This gravity produces tons & tons of heat and when the cloud of gas is dense enough, nuclear fusion occurs.
After fusion begins, there is stabilization between the tremendous inward pull of gravity & outward thermal pressure from fusion to create the young star which joins the main sequence.
Fission & Fusion
· The strong nuclear force is the attractive force that binds protons and neutrons together in the nucleus. Over very short distances (meaning smaller atomic #s), the strong nuclear force is much greater than the repulsive forces among protons & electrons.
· Fusion is the process in which the nuclei of two atoms combine to form a large nucleus. Fusion on stars is caused by hydrogen protons joining together producing massive amounts of energy.
· On stars, the fusion produces HELIUM
· Hydrogen has 1 proton, when two hydrogen atoms combine you get 2 protons in the nucleus which makes helium!
· Fission is the splitting of an atomic nucleus into two smaller parts. This produces TREMENDOUS amounts of energy out of very little mass like the atomic bomb!
Type of Star
A star’s mass (how much gas & dust came together) determines the star’s place on the main sequence and how long it will stay there.
· 3 Main categories of Stars
1. High Mass—Blue stars; they are the brightest, but will burn out quickly because they use up so much energy. Their mass is about 30x mass of the sun. They have temperatures of 30,000K and above.
2. Medium Mass—these are stars like the sun, yellow in color. They are generally stable. They last about 10 billion years and have temperatures of 5,000-6,000K
3. Low Mass—cool, long-lived stars. They are the least bright and are redder in color. They last about 100 billion years and have temperatures of about 3,000K and below
*The Low Mass stars last longer than High Mass stars because they are using less energy!
Death of Stars
· When stars run out of fuel or energy, they die. That does not mean they just disappear.
· Low Mass & Medium Mass stars eventually become white dwarfs which cool off to black dwarfs and High Mass stars become supernovas and sometimes will then turn into black holes
Properties of Stars
· Color & Temperature: The hotter or higher the temperature of a star, the brighter and more blue it is just like the blue part of a flame on a candle. Cooler stars become redder & less bright.
· Brightness: the apparent brightness is what we see from Earth. The apparent brightness of a star decreases as its distance increase. Absolute brightness is how bright a star really is.
· Size & Mass: can be determined from a star’s temperature and absolute brightness