V Physics - Astrophysics

Orbit of: Comets

• Shape is very elliptical

• Around the star

Orbit of: Moons

• More circular in shape

• Around their planet

Orbit of: Planets

• More circular

• Around the star

Equation linking: orbital speed, orbital radius and time period

v = 2πr/T

How are stars classified by their colour?

• Blue stars are the hottest

• In the middle is white and yellow

• Red stars are the coolest

Star Life Cycle Step 1

Protostar:

• Hydrogen dust clouds contract into a ball due to gravitational attraction

• As density and pressure increase, temperature starts to increase

Star Life Cycle Step 2

Main Sequence Star:

• The star fuses hydrogen into helium

• Inwards gravitational attraction balance by outwards radiation and pressure

• A star spends most of its life as a main sequence star

Star Life Cycle Step 3 - High Mass Stars

Red Supergiant (Bigger than Red Giant):

• The star begins to run out of hydrogen

• Inwards gravitation attraction is stronger than outwards radiation pressure, causing the star to contract

• As the star contracts, the temperature increases and the remaining hydrogen in the outer layers begin to fuse, causing the star to expand and hence cool.

Star Life Cycle Step 4 - High Mass Stars

Supernova:

• The gravitational collapse of a high mass star is so fast and violent that a shockwave bounces off the core

• This explosion is called a supernova

Star Life Cycle Step 4 - High Mass Stars (Way 1)

Neutron Star:

• The gravitational attraction is so strong that electrons and protons are pushed together to form neutrons

Star Life Cycle Step 4 - High Mass Stars (Way 2)

Black Hole:

• Gravitational collapse is so strong that all matter gets crushed into a single, infinitely dense point

Star Life Cycle Step 3 - Low Mass Stars

Red Giant:

• The star begins to run out of hydrogen

• Inwards gravitation attraction is stronger than outwards radiation pressure, causing the star to contract

• As the star contracts, the temperature increases and the remaining hydrogen in the outer layers begin to fuse, causing the star to expand and hence cool.

Star Life Cycle Step 4 - Low Mass Stars

White Dwarf:

• A low mass star will not have enough gravitational attraction to heat up the centre of the star to fuse the built-up carbon.

• The outer layers have been blown away and will make up the building blocks of planets in millions of years, called a planetary nebula

Absolute Magnitude Scale

-10 → +15 : bright → dim

Hertzsprung-Russell diagram

Red Shift

Astronomers have discovered that, in general, the further away a galaxy is, the more red-shifted its light is. This means that the further away the galaxies are, the faster they are moving. Red-shift data provides evidence that the Universe, including space itself, is expanding.

Cosmic Background Radiation (CMBR)

• Empty space is full of electromagnetic waves of microwave wavelength

• Universe started very hot and as it expanded it cooled

• At the very hot temperatures, protons and neutrons were able to fuse

• When the temperature dropped, hydrogen and helium gas were formed. This is when raw material of stars was made.

• When neutral atoms were formed, all the high energy gamma rays were free to propagate rather than constantly colliding with particles and the universe became transparent.

• As it continued to expand, the gamma rays became stretched out - so much that they became microwaves: finding these leftover microwaves supports the Big Bang theory.

Equation linking: change in wavelength, wavelength, velocity of a galaxy and the speed of light

change in wavelength / reference wavelength = velocity of a galaxy / speed of light

Speed of Light

3×10^8