Stars Flashcards
Describe the life cycle of a star
Stars initially form from clouds of dust and gas. The force of gravity makes the gas and dust spiral together to form a protostar.
Gravitational energy is converted into heat energy, so the temperature rises. If the temperature is high enough, hydrogen nuclei undergo fusion to form a helium nuclei. This gives out massive amounts of heat and light. A star is born! Smaller masses of gas and dust may also pull together to make planets that orbit the star.
The star immediately enters a long stable period, where the heat created by nuclear fusion provides an outward pressure to balance the force of gravity pulling everything inwards. The star maintains its energy output for millions of years, fur to the massive amounts of hydrogen if consumes. In this stable period, it is a main sequence star.
And it lasts several billions of years.
Eventually the hydrogen begins to run out. Heavier elements are made by the nuclear fusion of helium. The star then swells into a red giant( if small star). Or red supergiant( if big star). It becomes red because the surface cools.
A SMALL to MEDIUM sized star then becomes unstable and ejects its outer layer of dust and gas as planetary nebula. This leaves behind a dense,solid core- a white dwarf, which just cold form into a black dwarf.
In Big stars- the star glows brightly again, as they undergo more fusion and expand and contract several times, forming elements as heavy as iron in nuclear reactions. Eventually they explode in a supernova, forming elements heavier than iron and ejecting them into the universe to form new planets and stars.
The exploding supernova throws the outer layers of dust and gas into space,leaving a very dense core called a neutron star.
If the starved big enough this will become a black hole.
What is a galaxy?
A galaxy is a collection of billions of stars held together by gravity.
Why can’t nuclei larger the iron be formed by fusion?
Too much energy is needed.
The enormous force off the collapse fuses small nuclei into large ones in a supernova.
What is the heaviest know natural element?
Uranium
