what mechanism make them to re-explode? what are symbiotic novae ?
White Dwarfs can go nova by accreting hydrogen from a neighbouring star; the gas is compressed by the extreme gravity of the white dwarf causing a thermonuclear runaway explosion on the surface (temperatures up to 20 million k). During a nova explosion, the energy released can equal what the sun emits over 10,000 years. The mass ejected only makes up about 1/10,000th of the white dwarfs mass, which means the star stays intact and can return to its prenova state. The process can be repeated every few thousand years.
except wiki where i can find a nice article on nova?
The 'cosmic cinema' by the Max Planck Institute also has a short, low res video regarding Nova-
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