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
Other theories involve a late helium flash
in the core of a dying giant.
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.