Astronomy – GCSE Physics

• A glowing ball of hot gas with a high amount of mass is called a Star.

• The most familiar star to us is Sun which give us light and warmth .

• Their are many galaxies in the Universe. Our galaxy is Milky way that contains billions of stars just like other galaxies.

• Though there are billions of stars in our Galaxy, a few thousands of them are visible to the naked eye from Earth.

• Stars shine because there is process that keeps on going on their surface that process is Nuclear Fusion.

• Stars seems to twinkle from Earth’s surface because the atmosphere contain many flying dust particles and due to the temperature conditions.

  

• Life Cycle of a star is  process which spans billions of years. The process contains gravitational collapse and nuclear fusion. The process happens in following stages –

Steller Nebulae(Birth): In the beginning there is a large cloud of dust particles and gas which we call as Nebulae. They are measured in light years(Astronomical distance unit). These Nebulae regions collapse due to gravitational forces which forms Protostars.      Example: Orion Nebulae

Protostar(Early Development): Protostar is a dense, hot core surrounded by dust and gas. Protostar is the early development phase of a star formation. When the core contracts due to gravitational forces then temperature rises and the process of nuclear fusion can start and then protostar becomes main sequence star.

Main Sequence(Stable Phase): When the environment of protostar is hot and exceeds a range of temperature, then nuclear fusion starts. The hydrogen gets converted into Helium and high energy is released and protostar becomes main sequence, the longest phase of star formation which lasts for billions of years. Here it shines brightly, our sun is currently in this phase.

Red Giant/Super Giant: Huge and massive stars used their fuel fastly, when the fuel is used star starts collapsing within itself.Stars having fuel for further fusion forms Red giant(lesser massive and red coloured) or Super giant(massive and blue coloured).

White Dwarf(medium or low mass stars): When the fuel is exhausted, including Helium, Red Giant becomes unstable and the outer layers move into space, forming planetary nebulae and then the core left behind is called white dwarf which is very dense. The mass of a typical white dwarf is half of the mass of Sun. The White Dwarf cools down over years and becomes Black Dwarf.

Super Nova(High Mass Stars): After the Super Giant stage the fusion continues  but further fusion needs  extra energy and then the core collapse resulting into a large explosion called  Supernova. The explosion is incredibly bright. The brightness may even outshine the galaxy for weeks.

Neutron Star/Black Hole: A Neutron Star is the result (remnant) of a big explosion(Supernova) of a massive star. A neutron star has a mass greater than the Sun, which is compressed into a sphere. A Neutron Star is composed of Neutrons (subatomic particles with no electrical charge).

A Black hole is a highly massive object in space with a powerful gravitational pull that even light can not escape it. There’s a boundary around Black Hole(event horizon) which warps spacetime. Anything that crosses that boundary can never come back from Black Hole.