Life Cycle of Star
Hi guuysss! Last time, we discussed about Appearance of Star that appears in the night sky so now, Let's move on to the next topic.
THE LIFE CYCLE OF STAR!
Outlined below are the many steps involved in a stars evolution, from its formation in a nebula, to its death as a white dwarf or neutron star.
NEBULA
A nebula is a cloud of gas (hydrogen) and dust in space. Nebulae are the birthplaces of stars. There are different types of nebula:
--An Emission Nebula e.g. such as Orion nebula, glows brightly because the gas in it is energised by the stars that have already formed within it.
--In a Reflection Nebula, starlight reflects on the grains of dust in a nebula.
Planetary Nebula are the outer layers of a star that are lost when the star changes from a red giant to a white dwarf.
STAR
A star is a luminous globe of gas producing its own heat and light by nuclear reactions (nuclear fusion).
They are born from nebulae and consist mostly of hydrogen and helium gas. Surface temperatures range from 2000�C to above 30,000�C, and the corresponding colours from red to blue-white.
RED GIANT
This is a large bright star with a cool surface. It is formed during the later stages of the evolution of a star like the Sun, as it runs out of hydrogen fuel at its centre. Red giants have diameter's between 10 and 100 times that of the Sun.
They are very bright because they are so large, although their surface temperature is lower than that of the Sun, about 2000-3000�C. Very large stars (red giants) are often called Super Giants
RED DWARF
These are very cool, faint and small stars, approximately one tenth the mass and diameter of the Sun. They burn very slowly and have estimated lifetimes of 100 billion years. Proxima Centauri and Barnard's Star are red dwarfs.
WHITE DWARF
White dwarfs are the shrunken remains of normal stars, whose nuclear energy supplies have been used up. White dwarf consist of degenerate matter with a very high density due to gravitational effects, i.e. one spoonful has a mass of several tonnes. White dwarfs cool and fade over several billion years.
SUPERNOVA
This is the explosive death of a star, and often results in the star obtaining the brightness of 100 million suns for a short time. There are two general types of Supernova:
Type I These occur in binary star systems in which gas from one star falls on to a white dwarf, causing it to explode.
Type II These occur in stars ten times or more as massive as the Sun, which suffer runaway internal nuclear reactions at the ends of their lives, leading to an explosion.
NEUTRON STARS
These stars are composed mainly of neutrons and are produced when a supernova explodes, forcing the protons and electrons to combine to produce a neutron star. Neutron stars are very dense. Typical stars having a mass of three times the Sun but a diameter of only 20 km.
BLACK HOLES
Black holes are believed to form from massive stars at the end of their life times. The gravitational pull in a black hole is so great that nothing can escape from it, not even light.
The density of matter in a black hole cannot be measured. Black holes distort the space around them, and can often suck neighbouring matter into them including stars.
THAT'S ALL. THANKYOU!
References:
http://www.cyberphysics.co.uk/graphics/diagrams/space/lifecycle_of_star.jpg
http://www.telescope.org/pparc/res8.html