If a massive star's remaining core mass after collapse is greater than about $3 M_{ ext{Sun}}$, what compact object forms?
Answer
A black hole
Following a supernova, the remnant core will become a neutron star unless its mass is greater than approximately 3 solar masses, in which case it becomes a black hole.

Related Questions
What entirely sets the dramatic, variable countdown for how long a star remains burning?Roughly what percentage of a star's existence is spent in the relatively stable main sequence phase?Which two stellar properties define the relationship used to calculate a main sequence star's main sequence lifetime?For main sequence stars less massive than about 10 solar masses, how does luminosity relate to mass ($L ext{ is proportional to } M^p$)?What element's fusion in the core causes energy absorption, leading to catastrophic collapse in massive stars?What structure do mid-sized stars, like the Sun, puff up into after their core hydrogen fuel is spent?What is the expected main sequence lifespan for the universe’s low-mass marathon runners, the Red Dwarfs?Considering its 10 billion year main sequence lifespan, approximately how many stable years does the Sun have remaining?If a massive star's remaining core mass after collapse is greater than about $3 M_{ ext{Sun}}$, what compact object forms?Since stellar evolution occurs too slowly for centuries of human observation, what crucial tool must astrophysicists rely on?