P16: Space :D Flashcards
What is a galaxy?
A massive group of stars
How do stars form?
Form from clouds of dust and gas (nebula) - gas is mainly hydrogen. Gravity causes cloud to collapse, as dust particles move faster, temperature rises to millions of degrees Celsius, forming a protostar. If the temp of a protostar gets high enough, then the hydrogen nuclei join together to form helium, through the process of nuclear fusion. The protostar turns into a star at this point, and nuclear fusion is now releasing a huge amount of energy
What are the two opposing forces acting on a star?
The force of gravity acts inwards and makes the star collapse.
Energy from nuclear fusion acts outwards and tends to make the star expand.
These tend to be balanced, so star is in equilibrium.
Describe the lifecycle of stars (same size as Sun)
At some point, hydrogen fuel runs out, and so the outward force due to fusion energy is less than the inward force due to gravity, causing the star to collapse inwards and causing its temperature to decrease. Now helium nuclei join to form heavier elements, and causes the star to expand and form a red giant. At some point, the red giant stops fusing helium, causing the star to shrink and form a white dwarf. This cools down and stops releasing any energy and forms a black dwarf.
Describe the lifecycle of stars (bigger size as Sun)
Once they run out of hydrogen, they leave the main sequence stage and expand into red super giants. Helium nuclei fuse together to form heavier elements. Nuclear fusion cannot make elements heavier than iron. At some point, the star stops carrying out nuclear fusion and explodes (supernova). Supernova temperature is high enough to produce elements heavier than iron, they are distributed throughout the universe. After supernova, either a neutron star (neutrons densely packed together) or black hole is formed.
What are geostational satellites?
Orbit over the same part of the Earth - one complete orbit takes 24 hours.
Describe the relationship between the orbital speed of a satellite and its distance from Earth
If its speed increases, then the radius must decrease. At a higher speed, a greater force of gravity is needed to prevent it from flying off into space. By moving closer to Earth, force provided by gravity is greater, so it stays in orbit.
What did astronomers notice about distant galaxies?
They produced longer wavelengths (red-shift)
Tells us that galaxies are moving away from each other so light waves are stretched. Galaxies with bigger red shift are moving away faster than galaxies which are closer.
This provides evidence that the universe is expanding.
Describe the Big Bang Theory
Scientists assumed that the rate at which expansion happens will slow down due to gravity, however studies show that its actually expanding faster which they can’t explain easily. Possible explanations include dark matter and dark energy which could explain why the expansion of the universe is speeding up.
