Stars and Galaxies

• Galaxies are a set of bodies consisting of millions of stars with gas and dust particles.
• Galaxies come in many forms such as Spiral, Elliptical, and Irregular.
• Spiral galaxies include Andromeda and The Milky Way.
• Elliptical galaxies include Ursa Major and Messier 87.
• Irregular galaxies include the Small Magellanic Cloud and the Large Magellanic Cloud.
• The Milky Way is a medium-large spiral galaxy and our solar system is located at the edge of one of the spiral arms.
• The Milky Way consists of approximately 200 billion stars.
• Stars have various characteristics such as colour, size, distance, brightness, and temperature.
• A star is formed from a nebula, which is a large cloud consisting of dust particles and gases such as hydrogen and helium.
• The gases and dust particles in a nebula are pulled by a strong gravitational force, causing it to form a globe.
• The strong gravitational force causes the globe of gas to shrink and compress until it becomes very dense and forms a core.
• The core shrinks and becomes dense due to the increasing strength of the gravitational force.
• When the temperature and pressure in the core become too high, a nuclear reaction will take place.
• Hydrogen gas turns into helium during the nuclear reaction, releasing a huge amount of heat energy and light.
• The core will shine and a star is formed.
• The star that is formed is known as a protostar.
• A new star continues to expand and becomes either an average star like the Sun or a massive star.
• In a star, a lot of heat is generated which heats up the outermost layer of the star.
• As a result of this heat, hydrogen within the outer layer of the star starts to burn.
• This causes the star to expand.
• During this stage, the star appears red in colour and is called a red giant.
• If the red giant is not massive, a white dwarf is formed.
• However, if the red giant is big enough, it contracts so quickly that a big explosion called a supernova occurs.
• A supernova is extremely bright and can be seen in daylight.
• As a result of the explosion, a neutron star is formed if the original star is a large star.
• If the original star is a super-large star, a black hole is formed.
• A black hole is called a black hole because light in it cannot escape.
• Any matter that enters a black hole cannot escape either.
• The Milky Way is a medium-sized spiral galaxy.
• Our solar system is located at the edge of one of the spiral arms of the Milky Way.
• The Milky Way consists of approximately 200 billion stars and the Sun is one of them.
• There are 3 types of galaxies: elliptical, spiral, and irregular.
• Example of spiral galaxies: Andromeda and Milky Way
• Examples of Elliptical galaxies: Ursa Major and Messier 87
• Examples of Irregular galaxies: Large Magellanic Cloud and Small Magellanic Cloud
• Stars can be classified based on their colours which correspond to their surface temperature, which ranges from a lower to higher temperature.
• Red stars have a temperature of less than 3,500 degrees Kelvin.
• Blue stars have a temperature of 11,000 to 25,000 degrees Kelvin.
• White stars have a temperature of 6,000 to 7,500 degrees Kelvin.
• Stars can be classified based on their colour and temperature.