By: Kae-kae14 & Dae-Dae15 Lifecycle of a Star

Life Cycle of a star

Nebula It is a cloud of gas and dust Its about 7,000 light-years from Earth A nebula is made up of hydrogen gas and plasma. It is the first stage of a star’s cycle.

Protostar A protostar is a large object that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. Protostars are often hard to see. They are hidden deep inside a big dusty gas cloud.

Brown dwarf Brown dwarfs are often thought of as "stillborn" stars. They have masses that range from twice the mass of Jupiter and 0.08 times the mass of our sun. It form into the same manner as stars, from a collapsing cloud of dust and gas.

Main Sequence Star The main sequence is a continuous and special band of stars that appear on plots of stellar color versus brightness. After a star has formed, it generates energy at the hot, dense core region through the nuclear fusion of hydrogen atoms into helium. ophysics/stellarevolution_postmain.html

Table of a main sequence Star This is a table of a main sequence star.

Hydrogen fusion In 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. The important thing to remember is that this fusion cycle releases energy in the core of the star. It is this fusion cycle that generates energy in our Sun. We know of this energy when we feel hot on Summer days! This whole process happens in three steps. There are animations of the three steps below to help you visualize this process! olar_interior/Nuclear_Reactions/Fusion/Fusion_in _stars/H_fusion.html

Supergiant and Red giant Super giants are among the most massive stars. Because of their extreme masses they have short life spans of 30 million years down to a few hundred thousand years. A red giant is a luminous giant star of low or intermediate mass. The most common red giants are the so-called red giant branch stars (RGB stars) whose shells are still fusing hydrogen into helium, while the core is inactive helium. Red giants are stars with radii tens to hundreds of times larger than that of the Sun which have exhausted the supply of hydrogen in their cores and switched to fusing hydrogen in a shell outside the core.

Helium Fusion Helium fusion is a kind of nuclear fusion, with the nuclei involved being helium. If the core temperature of a star exceeds 100 million Kelvin's (100 megakelvins), as may happen in the later phase of red giants and red supergiants, then a third helium nucleus has a significant chance of fusing with the beryllium-8 nucleus before it breaks down, thus forming carbon-12.

Supernova A supernova is when a very big star explodes. This happens when a star totally runs out of energy to fuse. Only stars that were giants all of their lives explode. The biggest of these stars we know of are called Hyper giants and smaller ones are called super giants. Supernova explosions happen rarely. tc.pbs.org/wgbh/nova/gamma/images/cosm_supernova2_large.jpg

Planetary Nebula planetary nebula is an emission nebula consisting of a glowing shell of gas and plasma formed by certain types of stars when they die. Planetary nebulae are important objects in astronomy because they play a crucial role in the chemical evolution of the galaxy, returning material to the interstellar medium which has been enriched in heavy elements and other products of nucleosynthesis (such as carbon, nitrogen, oxygen and calcium) _hst_full.jpg

White Dwarf A white dwarf is a star. The color of a white dwarf is most likely the Same but not as bright. White dwarfs are not very bright because they are smaller than many other stars

Black Dwarf A 'black dwarf' is a white dwarf that has cooled down enough that it no longer emits light. The difference between a White dwarf and a black dwarf Is that the black dwarf is cold And the white dwarf is hot.

Black Hole Black holes are objects so dense that not even light can escape their gravity, and since nothing can travel faster than light, nothing can escape from inside a black hole. For example, For example, if our Sun was magically crushed until it was about 1 mile in size, it would become a black hole, but the Earth would remain in its same orbit. hole.jpg

Neutron Star A neutron star is a type of leftover 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 with zero 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 requires that no two neutrons can occupy the same quantum state simultaneously. /2007/08/21/neutron_star_1_2.jpg

Evolution of a Low-Mass star Low mass stars, like every other star, begin life as a part of an Interstellar Cloud. As the cloud picks up stellar dust and other space junk the increasing gravity causes the cloud to collapse. As it collapses the cloud becomes smaller and hotter. After a few million years the low mass star begins to fuse helium into hydrogen. When this happens the collapse is ended because the fusion raises the pressure inside the star. During this period the star is commonly referred to as a Protostar. When the star burns about 90% of the hydrogen in its core, the core will shrink, burning the hydrogen even more quickly, generating more energy. As this energy flows outward it pushes out the stars outer layers. When the outer layers cool away from the core they turn red, at this time the star is called a Red Giant. pics/lowmassstars/lowmassstars.html

High-Mass stars A High Mass Star begins life the same as a Low Mass Star. The star is formed from a bigger clump than the Low Mass Star. which compresses the clump, which in turn superheats the massive clump. When the clump becomes a main- sequence star, it is much hotter, bluer, and more luminous than the Sun. As the High Mass Star runs out of hydrogen it swells and grows cooler, much the same as a Low Mass Star. The evolutionary difference is that the High Mass Star passes through a pulsating Yellow Giant phase before it becomes a Red Giant. The greater mass of the star creates an intense gravitational compression of the star's core. As the core is compressed, the temperature rises and fuel is burned at a frenzied pace in order to maintain the pressure that supports the star. pics/highmassstar/highmassstars.html

Done By: kae-kae14 & dae-dae15 THE END