8.1 - solar system, life cycle of stars

space physics: the solar system, the life cycle of stars

what is a galaxy?

a massive group of stars

which galaxy is our solar system a part of?

the Milky Way Galaxy

what is the solar system?

• our planetary system, which is the Sun and everything else that orbits it.

what does our solar system consist of?

• at the centre is our star, the Sun.

• 8 planets plus dwarf planets that orbit the Sun.

• moons, aesteroids and comets

what are the 8 main planets in our solar system?

• Mercury, Venus, Earth, Mars: relatively small rocky planets.

• Jupiter, Saturn, Uranus, Neptune: larger, gaseous planets.

what is a natural satellite?

a large body that orbits a planet in the solar system, and is usually significantly smaller than this planet

what is a dwarf planet?

a body similar to a planet but too small to be called a planet.

examples: Pluto, Ceres, Eris

For a while Pluto was considered the 9th planet in our solar system, but it was reclassified as a dwarf planet. Why?

because Pluto was too small, and its natural satellite was 2/3 of its size.

where is the asteroid belt?

between the orbits of Mars and Jupiter

• dwarf planets are also found here too

how old is the Sun?

4.6 billion years

what stage of its life cycle is the Sun believed to be in right now?

it is believed to be half-way through its life cycle, in the main sequence stage.

why is the Sun ‘heliocentric’?

it lies at the centre of our solar system

what is a star?

a very large burning ball of burning gas that emits its own radiation and has a fixed position in space

what is a nebula?

a cloud of dust and gas, where the gas is mainly hydrogen

how was the Sun formed?

The Sun was formed from a nebula pulled together by the gravitational force of attraction between the dust and gas particles.

what is a star life cycle?

the stages that a star passes through its lifetime, which depends on the size of the star relative to the Sun

what is the beginning of the life cycle of all stars?

1. A nebula (a cloud of dust and gas) is present in a galaxy.

2. The gravitational attraction between the dust and gas particles pulls them together.

3. The nebula becomes hotter, denser, and has higher pressure as particles collide faster and are pulled close together.

4. The nebula rotates faster and eventually collapses to form a protostar.

5. If temperature and pressure is high enough, hydrogen nuclei fuse together to form helium nuclei, in nuclear fusion.

6. This nuclear fusion releases very huge amounts of energy.

7. The force due to fusion energy acting outwards opposes the force of gravitational collapse acting inwards, and these two forces balanced.

8. Equilibrium forms, causing a main sequence star to form.

what happens to stars during the main sequence phase?

1. Nuclear fusion continues in the main sequence star for billions of years, until eventually the star runs out of hydrogen to fuse.

2. This means the outward force due to fusion energy is less than the inward force of gravitational collapse, so there is no equilibrium.

3. The star becomes unstable then collapses inwards, which causes the temperature and pressure of the star to increase.

4. This allows for helium nuclei to fuse together to create heavier elements (up to iron).

what’s the rest of the life cycle of a star of the same size/magnitude as our Sun?

nebula → protostar → main sequence.

1. Helium nuclei fuse together to create heavier elements (up to iron).

2. The star expands to form a red giant.

3. At some point the red giant stops fusing helium nuclei and collapse, causing it to shrink/contract under gravity to form a white dwarf.

4. As the white dwarf isn’t carrying out nuclear fusion, it gradually cools down.

5. Eventually, it stops releasing any energy and forms a black dwarf.

what’s the rest of the life cycle of a star of the larger size/magnitude than our Sun?

(MASSIVE STARS)

nebula → protostar → main sequence.

1. Helium nuclei fuse together to create heavier elements (up to iron).

2. The star expands to form a red super giant.

3. At some point the red super giant stops fusing helium nuclei and explodes to produce a supernova.

4. Supernovae have very high temperatures that allow elements heavier than iron to form.

5. These new elements are ejected and distributed throughout the universe, where they can form new planets or stars.

6. After the supernova, the remains of the star can either form a neutron star or a black hole.

SUMMARY:

1. which 2 phases to all stars go through?

2. what do stars the same size as our Sun become?

3. what do stars bigger than our Sun become?

1. protostar and main sequence.

2. red giant → white dwarf → black dwarf.

3. red super giant → supernova → neutron star or black hole.

what is a supernova?

the explosion of a massive star (a star bigger than our Sun) which high temperatures and pressures that can produce elements heavier than iron, and distributes these elements throughout the universe.

what are the two possible products after a supernova?

• a neutron star, which consists of neutrons densely packed together.

• a black hole, which has such a large gravity that not even light can escape.

what type of force pulled together the cloud of dus and gas (nebula) to form the Sun?

gravitational force of attraction

what type of reaction occurs in stars as dust and gas is drawn together? what conditions are required for this to occur?

nuclear fusion reactions, which require very high temperatures and pressures

what do fusion reactions in stars produce?

hydrogen nuclei fuse to form heavier elements

• protostar: helium

• main sequence: elements heavier than helium, up to iron.

• supernova: elements heavier than iron.