The sudden onset of helium core fusion (or "burning") in post-main sequence stars is called the helium flash. It occurs in stars with mass less than about 2-3 solar masses once post-main sequence hydrogen shell burning has dumped sufficient helium nuclei into the core, heating it up to about 100 million K. Once the temperature is hot enough for helium fusion in one part of the core, the reaction quickly spreads throughout it due to the behaviour of the electron degenerate gas, the whole process taking minutes or hours.
runaway onset of helium fusion in the degenerate helium core of a low mass star.
The explosive ignition of helium burning that takes place in some giant stars.
in low-mass red giant stars, the onset of the fusing of helium in the core can be very rapid, almost explosive.
An explosive event in the post-main-sequence evolution of a low-mass star. When helium fusion begins in a dense stellar core, the burning is explosive in nature. It continues until the energy released is enough to expand the core, at which point the star achieves stable equilibrium again.
The nearly explosive ignition of helium in the triple-alpha process in the dense core of a red giant star.
A Helium flash is the sudden beginning of helium burning in the core of intermediate mass stars, or on the surface of an accreting white dwarf star.