HYDROGEN BURNING - Processes by which hydrogen (1H) is fused into helium (4He) with in a star.
Hydrogen Burning
The fusion of hydrogen into helium and the process by which all main-sequence stars generate energy. Every star born with more than 0.08 solar masses burns hydrogen.
Hydrogen-Deficient C-type Stars ...
core hydrogen burning The energy burning stage for main sequence stars, in which the helium is produced by hydrogen fusion in the central region of the star.
A normal hydrogen burning star such as our sun, occupies a place somewhere low and in the middle of the diagram. Giant luminous stars that are very hot are on the top left of the diagram.
At this point hydrogen burning in the core is no longer significant, and there is only a thin shell of hydrogen burning around the large helium core. The star is pretty much at the end of its Main Sequence life.
Gradually, the hydrogen burning in the shell around the solar core will increase the mass of the core until it reaches about 45% of the present solar mass.
hydrogen burning The fusion of hydrogen (protons) to helium in the core or shells of stars. Main sequence stars fuse hydrogen through the proton-proton chain or the CNO cycle. It is a nuclear reaction and not 'burning' or combustion with oxygen.
The successive nuclear fusion processes which occur inside stars are known as hydrogen burning (via the proton-proton chain or the CNO cycle), helium burning, carbon burning, neon burning, oxygen burning and silicon burning.
Meanwhile back down in the core of the star the hydrogen is all used up and hydrogen burning can no longer occur. Because there are no more nuclear reactions the core must contract.
This raises the internal temperature of the star and ignites a shell of hydrogen burning around the inert core.
It formed during hydrogen burning in main-sequence stars and red giants, via the CNO cycle. [C95] ...
Because of the large mass, after the hydrogen burning, the temperature and pressure of the core is high enough to trigger helium burning to carbon, and a hydrogen burning shell is developed around the core.
Thus, the star will have a helium burning core, a hydrogen burning shell which will provide most of the luminosity, and a large expanding envelope of outer atmosphere.
If a globular cluster is more than 10 million years old, then all of its hydrogen burning stars will be less massive than 10 solar masses. This implies that no individual hydrogen burning star will be more than 1000 times brighter than the Sun.
Eventually, helium in the core will exhaust itself at a much faster rate than the hydrogen, and the Sun's helium burning phase will be but a fraction of the time compared to the hydrogen burning phase.
The lifetime of a star in this hydrogen burning stage is very long (the Sun will last for billions of years before becoming a white dwarf) but eventually all the hydrogen in its interior will be used up and no further source of energy production will ...
Powerful magnetic fields might exist around the lowest mass stars, which are near the ignition threshold for hydrogen burning at their cores.
subgiant branch The section of an evolutionary track of a star that corresponds to changes that occur just after hydrogen is depleted in its core, and core hydrogen burning ceases.
its core temperature hits 10 million degrees.
hydrogen burning ignites in the stellar core.
all the hydrogen in the core is used up and the core contracts.
helium burning ignites in the core.
Protostar: A star that has not yet started core hydrogen burning.
Q
Quaoar: A planetoid in the Kuiper Belt on the edge of the solar system, about half the size of Pluto.
Having gone through 7 million years of its life as a hydrogen burning star and the last 700 000 years as a helium burning star, things start to happen in a hurry.
The locus in the H-R diagram where stars first reach stability as hydrogen burning stars.
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Glossary ...
The hydrogen burning stage is the longest thermonuclear stage for a star; it can last as short as several million years for the most massive stars, or as long as several hundred billion years for the least massive stars.
After a few dozen million years they use up their hydrogen in their centres and for a short time initiate helium burning in their cores while continuing hydrogen burning in their shells, which causes them to swell up into red supergiants.
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454. Zero-Age Main Sequence (ZAMS)
The locus in the H-R- diagram where stars first reach stability as hydrogen burning stars.
This causes the star to swell, destroying any nearby planets. This situation cannot last nearly as long as the hydrogen burning phase, and the star once again collapses. It is at this helium burning phase that Betelgeuse is currently at in its life.
At this temperature, nuclear fusion occurs, turning four hydrogen nuclei into a single helium nucleus plus a LOT of energy. This "hydrogen burning" releases gamma rays (high-energy photons) and neutrinos (particles with no charge and almost no mass).
" In these thermonuclear reactions, loosely called "hydrogen burning," four hydrogen nuclei are fused to form a helium nucleus (see nucleosynthesis). This point in time is conventionally called age zero.
 See also: Hydrogen, Star, Sun, Mass, Element
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