The Eagle Nebula
Main sequence star is born when hydrogen cloud is heated to very high temperature and the gas ignites into a fusion reaction in which hydrogen atoms combine into helium atoms (proton-proton chain) or the core burns in carbon cycle.
How the freezing cold dusty hydrogen gas cloud gets into fire?
Professor Kaler explains:
The clouds can be further compressed through collisions or by blast waves from exploding high-mass stars ( supernovae). Lumps of matter therefore form within the interstellar clouds. If their gravity is great enough, they can condense into one or more stars. Contraction causes more rapid spin, which creates a disk around the birthing star, from which it can draw matter. Further condensation within the disk can create planets (or even stellar companions). The contraction of forming stars raises the internal temperature, finally to the point of ignition of hydrogen fusion. Gravity would like to make the star as small as possible, but the fusion reactions stabilize it and keep it from contracting any further. The whole life story of a star from here on out is told by the battle between gravity and nuclear fusion, first one, then the other getting the upper hand. New high mass stars commonly light up their surroundings to produce diffuse nebulae like the Orion Nebula.
STARS
STARS
What is the most basic fusion in the universe, proton-proton chain?
[Proton-proton chain] begins when two protons (bare hydrogen atoms) ram together strongly enough to overcome the mutual repulsion caused by their positive electric charges and get close enough to stick together under the "strong force" (which operates only over a very short range).
One of the protons ejects its positive charge in the form of a "positron," a positive electron that hits a normal electron to generate energy in the form of gamma rays.
The conversion creates a deuterium (heavy hydrogen) nucleus as well as a tiny particle called a "neutrino." Detection of neutrinos on Earth allow us to "see" directly into the solar center.
The fusion of the deuterium with another proton produces a light form of helium (with two protons and one neutron), while the fusion of two light helium atoms into a normal helium atom with two protons and two neutrons (with the ejection of two protons) completes the process, each reaction generating heat and light as a result of a slight loss of mass.
STARS
One of the protons ejects its positive charge in the form of a "positron," a positive electron that hits a normal electron to generate energy in the form of gamma rays.
The conversion creates a deuterium (heavy hydrogen) nucleus as well as a tiny particle called a "neutrino." Detection of neutrinos on Earth allow us to "see" directly into the solar center.
The fusion of the deuterium with another proton produces a light form of helium (with two protons and one neutron), while the fusion of two light helium atoms into a normal helium atom with two protons and two neutrons (with the ejection of two protons) completes the process, each reaction generating heat and light as a result of a slight loss of mass.
STARS
In this way universe is full of helium factories shining brightly in the night sky. These hot fire balls are not homogeneous, however, as the enormous forces inside them create layered structures around the core, zones and spheres. For example, this is how the anatomy of Sun looks according to our present knowledge :
Image: Astronomy Know How
Star classes
The cores of main sequence stars are thus either making helium or carbon, depending on the mass of the heavenly body. The sequence includes star classes named by astronomers O B A F G K M L T from hottest and brightest to coolest and dimmest. (Sun is a G class star.)
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