Could you Explain The whole life Cycle of Stars ?

Answer 1

i dont know much but this may be will help, bon voyage
The Life and Death of Stars

Where are Stars Born?

Astronomers believe that molecular clouds, dense clouds of gas located primarily in the spiral arms of galaxies are the birthplace of stars. Dense regions in the clouds collapse and form "protostars". Initially, the gravitational energy of the collapsing star is the source of its energy. Once the star contracts enough that its central core can burn hydrogen to helium, it becomes a "main sequence" star.

Main Sequence Stars

Main sequence stars are stars, like our Sun, that fuse hydrogen atoms together to make helium atoms in their cores. For a given chemical composition and stellar age, a stars' luminosity, the total energy radiated by the star per unit time, depends only on its mass. Stars that are ten times more massive than the Sun are over a thousand times more luminous than the Sun. However, we should not be too embarrassed by the Sun's low luminosity: it is ten times brighter than a star half its mass. The more massive a main sequence star, the brighter and bluer it is. For example, Sirius, the dog star, located to the lower left of the constellation Orion, is more massive than the Sun, and is noticeably bluer. On the other hand, Proxima Centauri, our nearest neighbor, is less massive than the Sun, and is thus redder and less luminous.

Since stars have a limited supply of hydrogen in their cores, they have a limited lifetime as main sequence stars. This lifetime is proportional to f M / L, where f is the fraction of the total mass of the star, M, available for nuclear burning in the core and L is the average luminosity of the star during its main sequence lifetime. Because of the strong dependence of luminosity on mass, stellar lifetimes depend sensitively on mass. Thus, it is fortunate that our Sun is not more massive than it is since high mass stars rapidly exhaust their core hydrogen supply. Once a star exhausts its core hydrogen supply, the star becomes redder, larger, and more luminous: it becomes a red giant star. This relationship between mass and lifetime enables astronomers to put a lower limit on the age of the universe.
Death of an "Ordinary" Star

After a low mass star like the Sun exhausts the supply of hydrogen in its core, there is no longer any source of heat to support the core against gravity. Hydrogen burning continues in a shell around the core and the star evolves into a red giant. When the Sun becomes a red giant, its atmosphere will envelope the Earth and our planet will be consumed in a fiery death.

Meanwhile, the core of the star collapses under gravity's pull until it reaches a high enough density to start burning helium to carbon. The helium burning phase will last about 100 million years, until the helium is exhausted in the core and the star becomes a red supergiant. At this stage, the Sun will have an outer envelope extending out towards Jupiter. During this brief phase of its existence, which lasts only a few tens of thousands of years, the Sun will lose mass in a powerful wind. Eventually, the Sun will lose all of the mass in its envelope and leave behind a hot core of carbon embedded in a nebula of expelled gas. Radiation from this hot core will ionize the nebula, producing a striking "planetary nebula", much like the nebulae seen around the remnants of other stars. The carbon core will eventually cool and become a white dwarf, the dense dim remnant of a once bright star.

Death of a Massive Star

Massive stars burn brighter and perish more dramatically than most. When a star ten times more massive than Sun exhaust the helium in the core, the nuclear burning cycle continues. The carbon core contracts further and reaches high enough temperature to burn carbon to oxygen, neon, silicon, sulfur and finally to iron. Iron is the most stable form of nuclear matter and there is no energy to be gained by burning it to any heavier element. Without any source of heat to balance the gravity, the iron core collapses until it reaches nuclear densities. This high density core resists further collapse causing the infalling matter to "bounce" off the core. This sudden core bounce (which includes the release of energetic neutrinos from the core) produces a supernova explosion. For one brilliant month, a single star burns brighter than a whole galaxy of a billion stars. Supernova explosions inject carbon, oxygen, silicon and other heavy elements up to iron into interstellar space. They are also the site where most of the elements heavier than iron are produced. This heavy element enriched gas will be incorporated into future generations of stars and planets. Without supernova, the fiery death of massive stars, there would be no carbon, oxygen or other elements that make life possible.

The fate of the hot neutron core depends upon the mass of the progenitor star. If the progenitor mass is around ten times the mass of the Sun, the neutron star core will cool to form a neutron star. Neutron stars are potentially detectable as "pulsars", powerful beacons of radio emission. If the progenitor mass is larger, then the resultant core is so heavy that not even nuclear forces can resist the pull of gravity and the core collapses to form a black hole.

Answer 2

To summarise:
1. Cloud of hydrogen in space (there are lots of them)

2. Non-uniformities in the density of the cloud will be increased by gravity - so any patches where the gas is thickest will attract more gas due to the gravitational pull

3. As the dense patches get denser, they get hot. The hydrogen gas is under very great pressure due to it's own weight. The pressure gets so high that hydrogen atoms get pushed together so hard they fuse and become helium. The process is called nuclear fusion and produces a considerable amount of energy in the form of heat and light.

4. The new star has entered a phase called 'main sequence'. Our sun is in this phase. It can last from just a few million to billions of years, depending on the size of the star. The bigger the star, the shorter time it has. The main sequence is stable. The energy released by the nuclear reactions cancels out gravity and prevents collapse. This continues until just about all the hydrogen has been fused into helium.

5. When the star runs out of hydrogen, it leaves the main sequence and is no longer stable. As the fusions reactions begin to wind down, gravity is then able to collapse the star further under its own weight. At the increased pressure, helium fusion may occur, producing heavier elements. This buys the star a little more time.

6. Eventually no more nuclear fusions can occur. What happens next depends on the size of the star. Giant ones will explode in a supernova. Smaller ones (like our sun) will become a red giant, and then a white dwarf and slowly fade away.

Answer 3

This is not an easy question to answer answer, that's why you have such long, detailed answers. About six billion years ago there was a huge cloud of hydogen gas, when it reached a diameter of about four light years a centre of gravity began to draw the cloud towards it, this was a long, drawn out process as the molecules of gas inexorably moved towards the centre, as space in the centre began to get crowded the contraction speeded up and individual atoms began to rub against each other causing heat to generate. Gravity encreased rapidly and more heat caused atoms of gas to stick, fuse, together. Fusion causes radiation as matter is converted into pure energy, E=MC2, radiation is an outward pushing force and it became strong enough to counteract the inward force of gravity, the star entered a stable state and continued to fuse hydrogen at the rate of 4.000.000 tons per second into helium, the star remainded stable until the hyrogen became scarce, fusion could no longer be maintained at the same rate, radiation decreased, gravity once more crushed the core until the temperature rose to a point to fuse atoms into a heavier element, eventually the star reached a point where it was creating iron atoms, it had reached it's limit, nothing heavier than iron can be fused in a star. The temperature of the star was very high and it's mass had decreased to a point where radiation now began to cause the star to baloon up in size, from a diameter of about 800.000 miles it grew to about 180.000.000 miles, at this stage radiation was overcome by the remaining mass and the star was crushed into a white dwarf, a small hot body that eventually cooled into a cinder. Most ordinary stars have the same life span as our sun, huge stars live for a shorter time but wneb they die they collapse with so much force that a rebound effect takes place and the temperate reashes levels high enough to fuse elements heavier than iron, these heavy elements along with everything else in the star's outer layers are blownd off in a horrendous explosion that give off more radiation, for a brief period of time, tghan the combined radiation of all other stars in the galaxy, this event is called a super nova, what is left is a neutron star, a very massive object that will forever remain in space.

Answer 4

A star is a enormous mass of hydrogen which condenced under the force of its own gravity. The condensation stops when the material becomes dense enough to initiate nucleur fusion. This is an expansive force, and the star lives out the rest of its life balanced between the two forces.

These forces are not constant, however. Fusion begins as hydrogen is fused in helium. After a certain time, the helium begins to fuse into carbon and finally into iron. As denser elements are fused, it creates greater amounts of heat. The star then expands into what is known as a "red giant". Eventually the star fuses all the material necessary to keep it inflated, and gravity becomes the dominant force.

What happens next depends on the mass of the star.The larger the star is, the more gravity will compress it when it runs out of material to fuse. Ordinary fusion can not fuse iron. However, some stars collapse so rapidly the carbon and iron then begin fusing. This creates enormous amounts of energy as heavier elements like lead and gold are created. The star then expands in what is known as a nova. All the heavy elements on earth were created in a nova explosion of an ancient star.

If the contraction is slower, gravity dominates and a strange object known as a black hole develops. The gravity is so great a black hole can even capture light. It is now believed our galaxy contains a giant black hole at its center. Curiously, black holes do radiate energy. It is a form of X-ray known as hawkings radiation. This means a black hole will eventually evaporate into pure energy.

The size of a star is critical to what it eventually becomes. Stars with the mass of our sun end their lives as neutron stars. The gravity is not great enough to collapse them into a balck hole, but they become super dense objects the size of the earth. Stars smaller then the sun might become white dwarves. The smaller a star is, the slower it fuses hydrogen, and very small stars can have incredibly long lifetimes. Our sun will last about 10 billion years and then become a neutron star.

Answer 5

A star is a massive, luminous ball of plasma. Stars group together to form galaxies, and they dominate the visible universe. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth, including daylight. Other stars are visible in the night sky, when they are not outshone by the Sun. A star shines because nuclear fusion in its core releases energy which traverses the star's interior and then radiates into outer space. Almost all elements heavier than hydrogen and helium were created inside the cores of stars.

Astronomers can determine the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space. The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star that are determined by its evolutionary history include the diameter, rotation, movement and temperature. A plot of the temperature of many stars against their luminosities, known as a Hertzsprung-Russell diagram (H-R diagram), allows the current age and evolutionary state of a particular star to be determined.

A star begins as a collapsing cloud of material that is composed primarily of hydrogen along with some helium and heavier trace elements. Once the stellar core is sufficiently dense, some of the hydrogen is steadily converted into helium through the process of nuclear fusion. The remainder of the star's interior carries energy away from the core through a combination of radiative and convective processes. These processes keep the star from collapsing upon itself and the energy generates a stellar wind at the surface and radiation into outer space.[1]

Once the hydrogen fuel at the core is exhausted, a star of at least 0.4 times the mass of the Sun[2] expands to become a red giant, fusing heavier elements at the core, or in shells around the core. It then evolves into a degenerate form, recycling a portion of the matter into the interstellar environment where it will form a new generation of stars with a higher proportion of heavy elements.[3]

Binary and multi-star systems consist of two or more stars that are gravitationally bound, and generally move around each other in stable orbits. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution.[4]

Answer 6

firstly dense clouds clouds comes closer nd they comes closer with gravitational forces aft nuclear fusion reaction takes place and lots of energy is formed nd star is created ,aft many years stars energy decines nd reaction becomes over nd a white dwrf star is formed nd then black hole..

Answer 7

I agree with U_Mex and give him thumbs up. Here is his source again.

Answer 8

http://en.wikipedia.org/wiki/Stellar_evolution

This should cover it much better than anything besides a professor.