Why Are Some Stars Not on the Main Sequence Again Try to Give a Physical Reason for This

Equilibrium: Life Goal of a Star



Look at the diagram on the correct. There are essentially 2 sections of a star: the cadre (where fusion occurs), and an outer gaseous beat. The core serves every bit the gravitational �center� of the star. It is very hot and very dense. The outer shell is made of hydrogen and helium gas. This shell helps move heat from the core of the star to the surface of the star where energy in the form of light and rut is released into infinite.

The star�southward main goal in life is to achieve stability, or equilibrium . The term equilibrium does not mean that there isn�t any alter in the star. It simply means that in that location is non a internet overall change in the star. In a stable star, the gas pressure pushing out from the center is equal with the gravity pulling atoms in to the center � when these forces are equal, the star is at equilibrium.

Once a star reaches equilibrium for the first time, it volition start called-for (fusing) hydrogen into helium.

This 5-step procedure works like this:

1. Nuclear fusion. Gravity = gas force per unit area (equilibrium)
2. Out of fuel.
3. Fusion stops, temperature drops.
4. Core contracts (gravity pulling atoms in).
5. Increased temperature (more atoms, more than collisions) and density in the cadre reinitiates nuclear fusion, equilibrium is accomplished, and the cycle begins again at step 1.

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Interactive Lab

Come across the Equilibrium Bike in activeness!

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Considering interstellar medium is 97% hydrogen and 3% helium, with trace amounts of grit, etc., a star primarily burns hydrogen during its lifetime. A medium-size star will alive in the hydrogen stage, called the master sequence phase, for well-nigh 50 meg years. In one case hydrogen fuel is gone, the star has entered �old age.�

Permit�south see if you sympathize the relationships between gas pressure, temperature, and gravity equally it relates to equilibrium. Consider it a practise quiz so yous are fix for the one your instructor volition undoubtedly give to yous.

Afterward Main Sequence

What happens to a star after the main sequence phase? Onetime age and death! How long it takes for a star to die depends upon its initial mass. A lower-mass star similar the sun can survive for billions of years, but after the hydrogen and helium fuel is gone it cannot get hot plenty to fuse carbon.


This blazon of star dies by puffing off its outer layers to produce expanding planetary nebulae. These nebulae, which are the remains of dying stars, serve as the birthplace for future protostars.

In contrast with our sun, which is really a main sequence star, massive stars alive very brusk lives, mayhap but millions of years, before they develop expressionless iron cores and explode as a supernova. The cadre of a dying massive star may form a neutron star or black hole, but the outermost parts of the exploded star return to the interstellar medium from which they came.

Let�s look at the relationship between initial mass and length of star life. How long practice nigh stars survive? Millions to billions of years, depending upon the star�s �birth-mass.� Is bigger always better? Non with stars. The more mass a star has at nativity, the harder it is to keep that fusion reaction going. It may have more atoms, but the fusion reaction goes faster and therefore burns the star out faster than smaller stars. Bigger is not better in this case! Keep in mind that fusion is what allows a star to maintain equilibrium. If a star cannot achieve a hot enough temperature to initiate fusion, so it�s dying already. Fusion reactions need a fuel, and there are three master fuels that a star uses for fusion: hydrogen, helium, and carbon .

HYDROGEN Burning (Stable Star Life):

93% of interstellar matter is hydrogen gas. 3% of interstellar matter is helium gas. When a star forms, it has the same composition since it�s made of the dust and gasses in a nebula. Hydrogen gas (H₂) is split into single hydrogen atoms (H⁺). The basic hydrogen fusion reaction is as follows:

H₂ -> 2H⁺ + 2e^- (UV photons)
4H⁺ -> He + energy
(More detailed reaction hither)

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Test your knowledge!

So what happens when the star is out of hydrogen fuel? Without fuel, there is no burning (nuclear fusion). This fusion is what allows a star to maintain equilibrium.


Attempt to predict what will happen to the star at this point: Star Quiz (part 1)

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Source: http://aspire.cosmic-ray.org/Labs/OldStarLife/starlife_equilibrium.html

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