TOPIC 8 - SPACE PHYSICS Flashcards
What is the first stage in the life cycle of stars?
Stars initially form a cloud of dust and gas called nebula.
What is the second stage in the life cycle of stars? The formation of a protostar?
The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the star gets denser and more particles collide with each other. When the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei. This gives out a huge amounts of energy, which keeps the core of the star hot. A star is born.
What is the third stage in the life cycle of stars? The formation of a main sequence star?
The star enters a long stable period where the outward pressure caused by the nuclear fusion that tries to expand the star balances the force of gravity pulling everything inwards. In this stable period it’s called a main sequence star and it typically lasts several billion years.
What is the fourth stage in the life cycle of stars? The formation of red giants?
Eventually the hydrogen begins to run out. The star then swells into a red giant (if it is a small star) or a red super giant (if it is a larger star). It becomes red and the surface cools. Fusion of helium (and other elements) occurs. Heavier elements (up to iron) are created in the core of the star.
Fifth stage - what is a white dwarf?
A small-to-medium sized star like the Sun then becomes unstable and ejects its outer layer of dust and gas. This leaves behind a hot, dense solid core - a white dwarf.
Sixth stage - what is a black dwarf?
As a white dwarf cools down, it emits less and less energy. When it no longer emits a significant amount, it is called a black dwarf.
Fifth stage - what happens to red super giants (supernova)?
Big stars, start to glow brightly again as they undergo more fusion and expand and contract several times, forming elements as heavy as iron in various nuclear reactions. Eventually they will explode in a supernova, forming elements heavier than iron and ejecting them into the Universe to form new planets and stars. Stars and their life cycles produce and distribute all naturally occurring elements.
What do stars produce in their life cycle?
tars and their life cycles produce and distribute all naturally occurring elements.
Sixth stage - what happens during the exploding supernova?
The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star. If the star is massive enough, it will become a black hole - a really dense point in space that not even light can escape from.
What are planets?
Large objects that orbit a star. There are 8 in our solar system. Their gravity has to be strong enough to have pulled in any nearby objects apart from their natural satellites.
What are dwarf planets?
Planet-like objects that orbit stars, but don’t meet all of the rules for being a planet.
What are moons?
These are orbit planets. They are a type of natural satellite.
What are artificial satellites?
Satellites that humans have built. They generally orbit the Earth.
How is an orbit created?
If an object is travelling in a circle it is constantly changing direction, which means it is constantly accelerating. This means there is also a constantly changing velocity.
For an abject to accelerate, there must be a force acting on it. This force is directed towards the centre of the circle. This force would just cause the object to 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 (which is at a right angle to the acceleration) keeps it travelling in a circle.
The force that makes this happen is provided by the gravitational force between the planet and the Sun (or between the planet and its satellite).
What is the instantaneous velocity?
At a right angle to the acceleration.
