The Sun, Stars And Galaxy Flashcards
What is the significance of the The Sun‘s large mass
The fact that most of the mass of the Solar System is concentrated in the Sun is the reason the smaller planets orbit the Sun. The gravitational pull of the Sun on the planets keeps them in orbit
What is the position and percentage mass of the Sun
The Sun lies at the centre of the Solar System. The Sun is a star which makes up over 99% of the mass of the solar system.
What type of star is the sun
Medium star
The sun consists of which elements
Hydrogen and helium
Type of radiation from the sun
It radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum
How do colours and sizes classify stars
Stars come in a wide range of sizes and colours, from yellow stars to red dwarfs, from blue giants to red supergiants These can be classified according to their colour Warm objects emit infrared and extremely hot objects emit visible light as well Therefore, the colour they emit depends on how hot they are A star’s colour is related to its surface temperature A red star is the coolest (at around 3000 K) A blue star is the hottest (at around 30 000 K)
What is the significance of the nuclear fusion that occurs in the sun
provides a pressure that prevents the star from collapsing under its gravity
The milky way
Galaxies are made up of billions of stars
The Universe is made up of many different galaxies
The Sun is one of billions of stars in a galaxy called the Milky Way
Other stars in the Milky Way galaxy are much further away from Earth than the Sun is
Some of these stars also have planets which orbit them
Define one light year
The distance travelled by light through (the vacuum of) space in one year
Diameter of the Milky Way
The diameter of the Milky Way is approximately 100 000 light-years
This means that light would take 100 000 years to travel across it
Universal speed limit
The speed of light is the universal speed limit, nothing can travel faster than the speed of light
What is the distance of one light year
9.5 × 10^15m
How is a star formed
- Nebula
All stars form from a giant interstellar cloud of hydrogen gas and dust called a nebula - Protostar
The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas, known as a protostar. As the particles are pulled closer together the density of the protostar will increase. This will result in more frequent collisions between the particles which causes the temperature to increase - Main Sequence Star
Once the protostar becomes hot enough, nuclear fusion reactions occur within its core. The hydrogen nuclei will fuse to form helium nuclei. Every fusion reaction releases heat (and light) energy which keeps the core hot. Once a star initiates fusion, it is known as a main-sequence star
During the main sequence, the star is in equilibrium and said to be stable
The inward force due to gravity is equal to the outward pressure force from the fusion reactions. Once a protostar is formed, its life cycle will depend on its mass.
Life cycle of a low mass star
- Red Giant
After several billion years the hydrogen causing the fusion reactions in the star will begin to run out
Once this happens, the fusion reactions in the core will start to die down. This causes the core to shrink and heat up. The core will shrink because the inward force due to gravity will become greater than the outward force due to the pressure of the expanding gases as the fusion dies down. A new series of reactions will then occur around the core, for example, helium nuclei will undergo fusion to form beryllium. These reactions will cause the outer part of the star to expand. A low-mass star that is up to 8 times the mass of the Sun or smaller will become a red giant. It is red because the outer surface starts to cool - Planetary Nebula
Once this second stage of fusion reactions have finished, the star will become unstable and eject the outer layer of dust and gas. The layer of dust and gas which is ejected is called a planetary nebula - White Dwarf
The core which is left behind will collapse completely, due to the pull of gravity, and the star will become a white dwarf. The white dwarf will be cooling down and as a result, the amount of energy it emits will decrease - Black Dwarf
Once the star has lost a significant amount of energy it becomes a black dwarf. It will continue to cool until it eventually disappears from sight
Life cycle of a high mass star
- Red Supergiant
After several million years, the hydrogen causing the fusion reactions in the star will begin to run out
A high-mass star (one more than 8 times the mass of the Sun) will become a red supergiant. Similar to a low-mass star, the fusion reactions in the core will start to die down. The core will go through a series of periods of shrinking and heating up. As a result, the outer parts of the star will expand and contract. This time, fusion reactions will form elements all the way up to iron. Fusion reactions cannot continue once iron is formed - Supernova
Once the fusion reactions inside the red supergiant cannot continue, the core of the star will collapse suddenly and cause a gigantic explosion
This is called a supernova. At the centre of this explosion a dense body, called a neutron star will form
The outer remnants of the star will be ejected into space during the supernova explosion, forming new clouds of dust and gas (nebula). The nebula from a supernova may form new stars with orbiting planets - Neutron Star (or Black Hole)
In the case of the biggest stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole. A black hole is an extremely dense point in space that not even light can escape from
