<P> A star with mass greater than about 2.25 M starts to burn helium without its core becoming degenerate, and so does not exhibit this type of helium flash . In a very low - mass star (less than about 0.5 M), the core is never hot enough to ignite helium . The degenerate helium core will keep on contracting, and finally becomes a helium white dwarf . </P> <P> The helium flash is not directly observable on the surface by electromagnetic radiation . The flash occurs in the core deep inside the star, and the net effect will be that all released energy is absorbed by the entire core, leaving the degenerate state to become nondegenerate . Earlier computations indicated that a nondisruptive mass loss would be possible in some cases, but later star modeling taking neutrino energy loss into account indicates no such mass loss . </P> <P> In a one solar mass star, the helium flash is estimated to release about 7041500000000000000 ♠ 5 × 10 J, or about 0.3% of the energy release of a 7044150000000000000 ♠ 1.5 × 10 J Type Ia supernova, which is triggered by an analogous ignition of carbon fusion in a carbon--oxygen white dwarf . </P> <P> When hydrogen gas is accreted onto a white dwarf from a binary companion star, the hydrogen can fuse to form helium for a narrow range of accretion rates, but most systems develop a layer of hydrogen over the degenerate white dwarf interior . This hydrogen can build up to form a shell near the surface of the star . When the mass of hydrogen becomes sufficiently large, runaway fusion causes a nova . In a few binary systems where the hydrogen fuses on the surface, the mass of helium built up can burn in an unstable helium flash . In certain binary systems the companion star may have lost most of its hydrogen and donate helium - rich material to the compact star . Note that similar flashes occur on neutron stars . </P>

Where does the helium that is formed during hydrogen fusion go