THE STAR LIFE CYCLE

NEBULAA 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 energized by the stars that have already formed within it.

In a Reflection Nebula, starlight reflects on the grains of dust in a nebula.

PROTOSTARA protostar is a large object that

forms by contraction out of the gas of a giant molecular cloud in the interstellar medium.

The protostellar phase is an early stage in the process of star formation.

It starts with a core of increased density in a molecular cloud and ends with the formation of a T Tauri star, which then develops into a main sequence star. This is heralded by the T Tauri wind, a type of super solar wind that marks the change from the star accreting mass into radiating energy.

BROWN DWARFA black dwarf is a hypothetical

stellar remnant, created when a white dwarf becomes sufficiently cool to no longer emit significant heat or light.

Since the time required for a white dwarf to reach this state is calculated to be longer than the current age of the universe of 13.7 billion years, no black dwarfs are expected to exist in the universe yet, and the temperature of the coolest white dwarfs is one observational limit on the age of the universe.

MAIN SEQUENCEAfter a star has formed, it creates energy at the hot, dense core

region through the nuclear fusion of hydrogen atoms into helium. During this stage of the star's lifetime, it is located along the main sequence at a position determined primarily by its mass, but also based upon its chemical composition and other factors.

All main sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward gravitational pressure from the overlying layers.

HYDROGEN FUSIONIn the basic Hydrogen fusion cycle, four Hydrogen nuclei

(protons) come together to make a Helium nucleus. This is the simple version of the story.

There are actually electrons, neutrinos and photons involved that make the fusion of Hydrogen into Helium possible.

RED GIANTThis 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 are 10 and 100 times larger than our 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.

HELIUM FUSIONThe fusion of helium-4 nuclei (alpha particles) is known as

the triple-alpha process, because fusion of just two helium nuclei only produces beryllium-8. If the core temperature of a star exceeds 100 million Kelvin's (100 megakelvins.

Depending upon the temperature and density, an additional helium nucleus may fuse with carbon-12 to form oxygen-16, and at very high temperatures, additional fusions of helium to oxygen and heavier nuclei may occur.

PLANITARY NEBULAA planetary nebula is an emission nebula consisting of a glowing shell

of gas and plasma formed by certain types of stars when they die. The name originated in the 18th century because of their similarity in

appearance to giant planets when viewed through small optical telescopes, and is unrelated to the planets of the solar system.

They are a relatively short-lived phenomenon, lasting a few tens of thousands of years, compared to a typical stellar lifetime of several billion years.

WHITE DWARFA white dwarf, also called a degenerate

dwarf, is a small star composed mostly of electron-degenerate matter.

They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth.

Its faint luminosity comes from the emission of stored thermal energy.

White dwarfs comprise roughly 6% of all known stars in the solar neighborhood.

The unusual faintness of white dwarfs was first recognized in 1910 by Henry Norris Russell, Edward Charles Pickering, and Williamina Fleming. the name white dwarf was coined by Willem Luyten in 1922.

http://antwrp.gsfc.nasa.gov/apod/image/9612/ngc2440_hst2.jpg

BLACK DWARFA black dwarf is a hypothetical

stellar remnant, created when a white dwarf becomes sufficiently cool to no longer emit significant heat or light.

Since the time required for a white dwarf to reach this state is calculated to be longer than the current age of the universe of 13.7 billion years, no black dwarfs are expected to exist in the universe yet, and the temperature of the coolest white dwarfs is one observational limit on the age of the universe. http://naasbeginners.co.uk/MESSIEROBJECTS_files/

M57.jpg

HIGH MASS STARS

http://lcogt.net/files/jbarton/crab%20nebula.jpg

MASSIVE MAIN SEQUENCEA massive main sequence star is just a bigger

main sequence star that dies faster because it is bigger therefore it uses hydrogen and helium faster.

http://odin.physastro.mnsu.edu/~eskridge/astr101/kauf20_17a.JPG

http://www.mpia-hd.mpg.de/MCs_MPIA/figures/ngc346_xmm-ntt-irac.jpg

RED SUPER GIANTRed supergiant (RSGs) are supergiant stars (luminosity

class I) of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive. Betelgeuse and Antares are the best known examples of a red supergiant.

http://jso-mccabe.com/Img_2009/M48_Open_Cluster_Cropped_Text.jpg

SUPERNOVAA supernova is a stellar explosion. Supernova are extremely

luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. During this short interval, a supernova can radiate as much energy as the Sun could emit over its life span.

http://www.astronomyreport.com/Images/Young_Supernova_Remnant.jpg

NEUTRON STARA neutron star is a type of remnant that can result from the

gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event.

Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and roughly the same mass as protons.

Neutron stars are very hot and are supported against further collapse because of the Pauli exclusion principle.

This principle states that no two neutrons can occupy the same place and quantum state simultaneously.

http://www.dailygalaxy.com/my_weblog/images/2007/07/16/nasa_neutron_star_2.jpg

BLACK HOLEIn general relativity, a black hole is a region of space in which the

gravitational field is so powerful that nothing, not even light, can escape. The black hole has a one-way surface, called an event horizon, into which objects can fall, but out of which nothing can come.

It is called "black" because it absorbs all the light that hits it, reflecting nothing, just like a perfect black-body in thermodynamics.

Quantum analysis of black holes shows them to possess a temperature and Hawking radiation.

http://images2.fanpop.com/images/photos/3000000/Black-Hole-s-Galaxy-M64-space-3031378-520-584.jpg

RED DWARFThese 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.

URLS http://en.wikipedia.org/wiki/Black_hole

http://en.wikipedia.org/wiki/Helium_fusionhttp://en.wikipedia.org/wiki/Neutron_starhttp://en.wikipedia.org/wiki/Planetary_nebulahttp://en.wikipedia.org/wiki/White_dwarfhttp://en.wikipedia.org/wiki/Protostarhttp://en.wikipedia.org/wiki/Main_sequencehttp://en.wikipedia.org/wiki/Brown_dwarfhttp://en.wikipedia.org/wiki/Black_dwarfhttp://en.wikipedia.org/wiki/Red_gianthttp://en.wikipedia.org/wiki/Nebulahttp://en.wikipedia.org/wiki/Red_supergianthttp://en.wikipedia.org/wiki/Supernova