stars 6 marker

Question 1

Describe the evolution of stars of similar mass to the Sun 
through the following stages:
a nebula
b star (main sequence)
c red giant
d white dwarf

Answer 1

a) a nebula is a cloud of dust and gas. the gas is mostly hydrogen. the dust and gas can be pulled together by its own gravity. the hydrogen gets hotter as its gravitational potential energy is converted to kinetic energy.
b) the gas gets hot enough for the nuclei of hydrogen atoms in the gas cloud to fuse together. fusion reactions turn hydrogen atoms into helium and release a lot of energy. the star begins to shine. this stage of a stars life cycle is called a main sequence.
c) the star will have used up most of its hydrogen fuel. it swells up to become a red giant. other elements fuse together in a collapsing core of red giants.
d) elements that can take part in nuclear fusion reactions are used up. fusion reactions in the star stop. gravity pulls the material together to make a smaller white dwarf star. the star gradually cools down

Question 2

how is the evolution of stars with a mass larger
than the Sun is different, and may end in a black hole or
neutron star

Answer 2

a star with a higher mass than the sun follows the same first stages of the life cycle, but at each stage is shorter.when most of the hydrogen is used it forms a red super giant. at the end of this stage the star will explode into a supernova. if what remains after the explosion is less than four times the mass of the sun it will be pulled together by gravity to form a very small, dense star called a neutron star. more massive remnants form black holes.