I was reading some Wikipedia articles about astronomy, and came across an interesting line:
The neutron star may also accrete sufficient material to collapse into a black hole.
Now, here is my theory:
If a massive supergiant star ($>20 M_\odot$) has a neutron star at its core, eventually the neutron star will pass the TOV limit, collapsing into a black hole. So if the new black hole is still in the star's core, and the outer envelope is not ejected, will a modern quasi-star be formed? If so, how long would it live for?