1. LIFE CYCLE OF A STAR

2. 1. Star formation:A Nebula
A nebula is a cloud of gas and dust
Eagle nebula 1995: The natural color of the nebula is red, due to the predominance of hydrogen gas in the nebula. Ionized hydrogen emits most of its visible light in a specific color of red
The images depicts the finger-like protrusions from three enormous columns of cooler gas in the central region of the nebula. The central part of the nebula is being evaporated by ultraviolet radiation from the hot, young stars in the central open cluster. The pillars are cooler, more dense parts of the nebula that are resisting the evaporation. Within these pillars are clouds dense enough to begin gravitationally collapsing under their own weight and forming new stars.
Orion Nebula

3. Protostars
2. A protostar forms when the gases in a nebula condense due to an outside force such as an explosion acting upon it.
3. If the protostar’s center gets hot enough, nuclear fusion reactions will occur. When this fusion begins, a star is born.

4. Main Sequence Star
Animation of nuclear fusion
Stars shine by burning hydrogen. The process is called nuclear fusion. Hydrogen burning produces helium "ash." As the star runs out of hydrogen (and nears the end of its life), it begins burning helium. The ashes of helium burning, such as carbon and oxygen, also get burned. The end result of this fusion is iron. Iron cannot be used for nuclear fuel. Without fuel, the star no longer has the energy to support its weight. The core collapses. If the star is massive enough, the core will collapse into a black hole. The black hole quickly forms jets; and shock waves reverberating through the star ultimately blow apart the outer shells. Gamma-ray bursts are the beacons of star death and black hole birth.
4. Main sequence stage: During nuclear fusion, Hydrogen continues to be changed into Helium.

5. Red Giant and Super giant Phase
Red giants represent a late stage in the evolution of stars with a range of masses, from just under the mass of the Sun to tens of solar masses
The largest red giants, which form from the most massive of stars, are known as red supergiants. A red giant has exhausted its core supply of hydrogen and is now fusing hydrogen to helium in a shell outside the core. The nearest red giant to the Sun is Gacrux (Gamma Crucis).
Light Echoes From Red Supergiant Star V838 Monocerotis - December 2002
5. Giants and Supergiants: When most of the hydrogen in the star’s core has fused to helium the star expands becoming a giant or supergiant.

6. 6. Final Stage: White Dwarf:
A star enters the final stage of its life when its nuclear fuel is used up.
Less massive stars (like the sun), become white dwarfs, these are made entirely of a hot core.
Only the hot core of the star remains. This core becomes a very hot (T > 100,000K) young white dwarf, which cools down over the course of the next billion years or so
About 1,600 light-years away, two dense white dwarfs in the J0806 binary star system orbit each other once every 321 seconds. When they reach the end of their long evolutions, smaller stars typically become white dwarfs.

7. 7. Exploding Stars:
A supernova is an exploding star of incredible brightness. A supernova explosion blasts much of the star’s matter into space.
A supernova occurs when a star runs out of fuel, collapses under gravity and explodes
THE BRIGHTEST exploding star, or supernova, ever seen has been recorded by scientists from US space agency NASA, who report a similar event may be ready to go off in our own galaxy.
Astronomers say the finding of the supernova — known as SN 2006gy — suggests that violent explosions of massive stars were common in the early universe.

8. 8. Final Stage: Neutron Star:
A neutron star is an extremely dense star made entirely of tightly packed neutrons.
9. A pulsar is a neutron star from which radiation is received in regular rapid pulses.
Astronomers using NASA's Swift X-ray telescope have detected a neutron star within 250 to 1,000 light-years of Earth, making it the closest neutron star ever known. The object, located in the constellation Ursa Minor, is nicknamed Calvera, after the villain in the movie "The Magnificent Seven." If confirmed, it would be only the eighth known "isolated neutron star," or one that does not have supernova remnants, binary companions or radio pulsations.

9. 10. Final Stage: Black Hole:
September 4, 2008—A supermassive black hole at the center of the Milky Way has wound up in the crosshairs of a virtual telescope spanning 2,800 miles (4,506 kilometers).
Ground-based radio telescopes in Hawaii, Arizona, and California aimed at Sagittarius A*—also called A-star—obtained the image (above, a previous picture of the black hole).
The star is believed to mark the position of a black hole four million times the sun's mass.
Though unproven, there is strong evidence for the existence of black holes.
2. it’s 3.5 billion light years away, forming the heart of a quasar called OJ287. Quasars are extremely bright objects in which matter spiraling into a giant black hole emits large amounts of radiation.
A black hole is a collapsed object from which no light or matter can escape.
11. The more massive a star is, the shorter its life will be.