There are different ways a star can die:
- Unnova refers to the event where a star (given the right circumstances concerning its material density and orbital velocity) implodes directly into a black hole; without growing at all to a red-giant supernova phase first. As a result, the light and heat from the dying star disappears immediately. Whenever this happens, it does not affect any orbiting planets.
- The gravity of a black hole is equivalent to the gravity of the original star (assuming it hasn't gained/lost any mass during this transformation). So any planet orbiting the original star would not experience any different gravitational force from the resulting black hole; except that they would experience permanent darkness & eventually get colder (assuming they have no other source of heat due to internal radioactivity in their core or gravitationally induced friction from a tugging moon)!
- Blue stragglers are rejuvenated old stars that gained fresh material thereby becoming bigger and hotter... This additional supply of hydrogen gas could be sucked from a neighboring closely orbiting star in a binary system. The feeding smaller star eventually dies (becoming a White dwarf). However after the blue stragglers are eventually too old, the white dwarf can swallow hydrogen back from its bigger neighboring blue stragglers before it (the white dwarf) itself explodes in a nuclear blast (on a planetary size) innahialiting its companion blue straggler simultaneously.
