the life cycle of a star
DESCRIPTION
TRANSCRIPT
The Life cycle of a StarMuhammad JunaidBcs-A 22Im|sciences Peshawar
The Life cycle of a Star
Stars are born out of nebulae (a nebula is cloud of gas (mainly hydrogen) and dust.
Gravitational forces pull at the gas and dust compressing it into a slowly rotating globule.
The globule spins faster as it compresses
The spin-speed causes the pressure and temperature to increase .
The globule spreads out into a disk that becomes planets and a central core that becomes a star.
Fusion stage
When a temperature of about 27,000,000,000°F is reached, nuclear fusion begins.
This is the nuclear reaction in which hydrogen atoms are fused together to make helium atoms.
A lot of energy is given out as this happens.
The Stable stage
The fusion reaction produces radiation that causes an outward pressure called radiation pressure (blue arrows)
The Stable stage
The force of gravity that pulls all mass together causes an inward pressure (red arrows)
The star is in a stable state when the radiation pressure pushing outwards is equal to the gravitational pressure pushing inwards.
The bigger the Star the smaller its lifespan The most massive stars have the shortest
lives. Stars that are 25 to 50 times that of the
Sun live for only a few million years. Stars less massive than the Sun have even
longer life spans.
Death of a Star Size also determines what happens in
death …… When stars run out of fuel, they expand
to become Red Giants (larger ones into Super Red Giants!).
This happens because the radiation pressure is greater than the gravitational pull
Death of a Star
Larger stars then explode into a Supernova, smaller stars become a gas cloud.
Large stars then shrink into black holes whereas
Medium stars shrink into neutron stars and Small stars shrink into white dwarfs and
then cool into black dwarfs
Galaxies
Stars gather together in galaxies. There are billions of stars in each galaxy There are millions of galaxies in the
Universe Galaxies are often seen as spirals
with bright centres – the density of star material is greatest at the centre
a galaxy viewed from the edge
Galaxies are in constant motion