Sequence of the main phases of formation of a star: very slowly rotating cloud of gas, gravitational collapse, star formation by slow contraction and accretion with generation of intense stellar wind, collimation of the stellar wind into bipolar flow.
Click on image for full size
Image courtesy of the University of Oregon, Department of Physics, the Electronic Universe Project
The life cycle of the stars
A gas cloud, if big enough, starts to shrink. The density and temperature increase so nuclear fusion can start. This is when Hydrogen is converted into Helium.
The "burning" of Hydrogen stops the gas cloud from shrinking. At this point, the gas cloud becomes a star. This is the present state of our Sun.
After billions of years, most of the Hydrogen fuel has
been "burned", and the star begins to shrink again. The star has to turn to another source of fuel, Helium.
The next stage in the life of a star is called a red giant. The star here is much bigger than it was initially. When the red giant star runs out of fuel, the star begins to shrink again. This contraction heats up the core of the star enough so that the heavier elements can be made. When the star runs out of this type of fuel, it has neared the end of its life.
The star begins to throw off layers because it can't support them anymore. This is called a planetary nebula.
The core of the star becomes a white dwarf.
This is an extremely dense star the size of a planet.
Finally, when the white dwarf has used all its energy,
it stops shining and becomes a "black dwarf", a dead star.
This is expected to be the final state of our Sun.
For stars with higher masses than the Sun (up to about 40
times greater), the outer layers of the star may be thrown off with much more force.
This is a supernova. This type of star collapses down to a very compact size. This is what is called a "neutron star".
Stars bigger then 40 times the Sun may collapse into a "black hole".
You might also be interested in:
Nuclear fusion is a process where two or more nuclei combine to form an element with a higher atomic number (more protons in the nucleus). Fusion is the reverse process of nuclear fission. Fusion reactions...more
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...more
A Supernova is a very massive star that explodes at the end of its life cycle. The supernova is the furnace where the heavy elements (heavier than iron) are formed. ...more
Fusion in the core of stars is reached when the density and temperature are high enough. There are different fusion cycles that occur in different phases of the life of a star. These different cycles make...more
The Sun releases energy. The processes that make this energy take place in the center of the Sun. We can't see past the surface of the Sun. But scientists use indirect ways (diagnostics) to figure out...more
Neutron capture can occur when a neutron approaches a nucleus close enough for nuclear forces to be effective. The neutron is captured and forms a heavier isotope of the capturing element. When the new...more
IMF stands for Interplanetary Magnetic Field. It is another name for the Sun's magnetic field. The Sun's magnetic field is huge! It goes beyond any of the planets. The Sun's magnetic field got its name...more
The theory of relativity states that no particle can travel at the speed of light in a vacuum. However, light travels at lower speeds in dense media, like water. A particle traveling in water must have...more