SP5c Life Cycles of Stars

Question 1

Nebula?

Answer 1

.all stars are made from clouds of dust and gas (mainly hydrogen), called nebulae

Question 2

Protostar? (4)

Answer 2

.dust and gas spiral together
.gravitational attraction causes density to increase - particles collide more frequently and temperature rises
.when temperature and pressure inside the protostar get high enough, fusion reations start
.main sequence star is born

Question 3

Main sequence? (3)

Answer 3

.long stable period
.energy released in fusion provides an outward pressure that tries to expand the star (thermal expansion) which balances the force of gravity pulling everything inwards
.it is in equilibrium - doesn’t expand or contract

Question 4

State the evolution of stars of similar mass to the sun. (3)

Answer 4

red giant - white dwarf - black dwarf

Question 5

Red giant? (3)

Answer 5

.eventually, hydrogen in the core of a star begins to run out. The star is not hot enough and the force due to gravity becomes larger than the pressure of thermal expansion
.the outer layers of the star start to expand and cool, so it becomes a red giant
.helium and other light elements fuse to from heavier elements

Question 6

White dwarf? (3)

Answer 6

.red giant eventually runs out of lighter elements - nothing else in it will fuse
.it becomes unstable and throws off its outer layers as a planetary nebula
.this leaves behind the rest of the star, which is pulled together by gravity and collapses to from a very hot, dense and solid white dwarf

Question 7

Black dwarf?

Answer 7

.a white dwarf will eventually cool enough so that it stops glowing white hot

Question 8

What are the forces acting on a star in terms of thermal expansion and gravity?

Answer 8

.pressure outwards from the hot gases produced from fusion in the core
.gravity trying to compress them

Question 9

Explain how the balance of thermal expansion and gravity affects the life cycles of stars.

Answer 9

The balance of thermal expansion and gravity is essential for the stability and life cycle of stars. It determines how long a star remians on the main sequence, the type of nuclear reaction it undergoes and its ultimate fate.

Question 10

State the evolution of stars with a mass larger than the sun. (4)

Answer 10

red supergiant - supernova - neutron star or black hole

Question 11

Red supergaint? (2)

Answer 11

.stars with considerably more mass than the sun are hotter and brighter - they fuse hydrogen into helium much quicker and become red supergiants when the hydrogen starts to run out
.they then fuse heavier elements forming elements as heavy as iron and as they have far more fuel, they swell out to a much larger size, giving off a lot more energy

Question 12

Supernova? (2)

Answer 12

.core collapses and at a critical point this causes a massive shockwave or catalysmic explosion called a supernova
.supernovae create, fuse and eject the bulk of very high atomic mass elements such as gold or uranium

Question 13

Neutron star?

Answer 13

.this core is just lots of neutrons and nothing else. The resulting neutron star is extremely dense

Question 14

Black hole? (2)

Answer 14

.if the core left from a supernova is even more massive, it will continue to compress until the entire star collapses into an infinitely small point
.the gravitational field is now so strong, nothing can escape from it, not even light or electromagnetic radiation, presenting a black hole