n. (context astronomy English) The collapse, as opposed to a supernova explosion, of a star theoretically forming a black hole.
An unnova is an event at the end of a star's life when it collapses on itself without the emission of large numbers of particles and energy. This is unlike the mechanisms of high energy release during a nova or supernova. The centre of the unnova would form a neutron star or black hole, similar to that of a supernova. Matter from the outer part of the star may fall relatively slowly into the centre of the unnova, in which case low-energy gamma radiation may be emitted.