helium flash


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helium flash

n
(Astronomy) astronomy the explosive burning of helium in the case of a star of low mass that occurs when the core is so dense that the matter has become degenerate. The burning causes a rapid rise in temperature until it is so high that the gas ceases to be degenerate, after which there is a rapid expansion
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Eventually this increased density ignites the helium in an explosive pulse called a helium flash, pushing against the hydrogen shell so that it expands, becomes less dense, and stops burning.
It is highly unlikely that a CME contains any substantial amount of heavier elements, especially considering that the sun has not yet arrived at the point of helium flash and thus cannot begin to fuse elements heavier than helium.
However, after they leave the main sequence and start to climb the Hertsprung-Russell diagram (HRD) they do not undergo a helium flash as do their less massive cousins (Figure 1).
The Helium Flash "After a star of Population II has evolved away from the main sequence of the Hertzsprung-Russell diagram and become a red giant star, a remarkable 'thermal runaway' occurs deep in its interior.
The star now starts to shed its outer layers in a series of thermal pulses akin to the helium flash. Initially, these are quite small and only a few light hours across but in due course they expand to light years across and form what we see as a planetary nebula (Figures 20 and 21).
Other theories involve a late helium flash in the core of a dying giant.
If you know "Mu Cephei" as the Garnet Star you're all set, but you won't find it under "M"; and the "helium flash" entry doesn't inform you that the book also discusses "final helium flash" or that you should look up "Sakurai's object" to learn about the only example of the latter phenomenon that astronomers have had the opportunity to study since the advent of electronic light detectors.
They propose that V838 Mon is a dying supergiant caught at the moment of the fourth and final "helium flash" in its core, "resulting in the ejection of what may become a planetary nebula."
The researchers say the expansion velocity of the ejected material is much lower than in a classical nova, much less a supernova, nor does the light curve match the so-called helium flash of an evolved Sun-like star about to produce a planetary nebula and turn into a white dwarf.
Astronomers aren't sure exactly what happens near the end of the red-giant era because no one yet has a convincing model for the events associated with the "helium flash"--the first ignition of the helium in the core that's left over from hydrogen burning.