Final answer:
In a close binary system, a white dwarf can produce a nova or a Type Ia supernova when it accretes matter from its companion giant star, depending on the rate of accretion. Slow accumulation of hydrogen may lead to nova explosions, while rapid accretion or merger with another white dwarf can push it over the Chandrasekhar limit, causing a devastating Type Ia supernova.
Step-by-step explanation:
When a white dwarf accretes matter from its companion giant star in a close binary system, several outcomes are possible dependent on the rate of accretion. If the white dwarf slowly accumulates material, the hydrogen layer increases in temperature leading to a point where fusion begins explosively, causing a nova. This blasts much of the accumulated material away, potentially repeating if more matter from the companion star accumulates on the white dwarf.
However, if the rate of accretion is faster, the white dwarf can gain enough mass to exceed the Chandrasekhar limit, which is approximately 1.4 times the mass of our Sun (M_sun). At this point, it can no longer support its own gravitational force, contracts, and heats up until it triggers a catastrophic fusion reaction, effectively destroying it in a Type Ia supernova explosion. This violent end not only annihilates the white dwarf but distributes heavy elements into space at incredibly high velocities.
The other possible outcome for the white dwarf to become a Type Ia supernova is the direct merger with another white dwarf in a binary system. These events are significant as they contribute to the understanding of stellar evolution and serve as 'standard candles' for measuring cosmic distances.