Topic 8 - Space Physics

What is the Life Cycle of Stars?

1. Nebula - Stars initially form from a cloud of dust and gas.

2. Protostar - Gravity pulls the dust and gas together to form a protostar.

3. Temperature rises as the star gets denser causing more particles to collide, eventually leading to nuclear fusion of hydrogen nuclei creating helium nuclei.

4. This releases lots of energy keeping the core hot, creating a star.

5. Main Sequence Star - The star enters a long stable period where outward pressure caused by the fusion that tries to expand the star balances gravity pulling it together. It usually lasts several billion years (The Sun is in this stage).

6. Red Giant - Once hydrogen in the core is depleted, the star swells into a Red Giant/Super Red Giant. It becomes red due to the surface cooling. Fusion of helium occurs and heavier elements are created in the core.

7. White Dwarf/Black Dwarf - After the red giant phase, the outer layers are shed as it becomes unstable, and the remaining core becomes a white dwarf, which will eventually cool and fade into a black dwarf

8. Red super giants start to glow brightly again as they undergo more fusion and expand and contract multiple times, forming elements as heavy as iron in nuclear reactions.

9. Supernova - Eventually it explodes, forming elements heavier then iron and ejecting them into the universe to form new planets and stars.

10. Neutron Star/Black Hole - The exploding supernova throws the outer lauers of dust and gas into space, leaving a very dense core called a neutron star. If it big enough it will become a black hole.

What is a Black Hole?

A super dense point in space that not even light can escape from

What orbits our Solar System?

Planets - Large objects in which their gravity is strong enough to have pulled in any nearby objects apart from natural satellites

Dwarf planets - Planet-like objects that orbit stars but don’t meet the requirements to be a planet

Moons - Objects that orbit planets and are natural

Artificial Satellites - Objects that humans have built that orbit in space

How does something orbit?

If an object is travelling in a circle it is constantly changing direction, which means it is constantly accelerating. This means it is constantly changing velocity.

For an object to accelerate, there must be a force acting on it. This force is directed towards the centre of the circle

This force would cause the object to just fall towards whatever it was orbiting, but as the object is already moving, It just causes it to change direction.

The object keeps accelerating towards what it is orbiting but the instantaneous velocity keeps it travelling in a circle.

This force is Gravity.

How does speed change with orbit?

The closer you get to a star/planet, the stronger the gravitational force is.

The stronger the force, the faster the orbiting object needs to travel to remain in orbit.

For an object in a stable orbit, if the speed of the object changes, the size of its orbit must do so too. Faster moving objects will move in a stable orbit with a smaller radius than slower moving ones.

What is Red-shift?

The shift in observed wavelength of light from a source moving away from a stationary observer. The wavelength is shifted towards the red end of the electromagnetic spectrum.

Why does the Universe seem to be Expanding?

The Universe appears to be expanding due to the observation of red-shift in distant galaxies, indicating that they are moving away from us. This phenomenon suggests that space itself is stretching, causing galaxies to recede from one another.

What is the Big Bang Theory?

Initially, all the matter in the universe occupied a singular point which was very dense and so very hot. It then exploded, causing the expansion of the universe and the formation of matter as it cooled.

What is Dark Matter and Dark Energy?

Dark Matter refers to the unseen mass that does not emit light or energy, making it undetectable by current instruments

Dark Energy is the mysterious force driving the accelerated expansion of the universe.