The concept of black holes was first thought of by Albert Einstein in 1916, and the term itself was coined only half a century later by American astronomer John Wheeler. It was a few years before that, in 1964, when the first black hole was discovered, Cygnus X-1, and we have been trying to study black holes ever since. To summarize what we know about black holes so far, XKCD created this lovely table for comparison between black holes and regular holes. - via Kottke
(Image credit: XKCD)
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"When the progenitor star is below about 20 M☉ – depending on the strength of the explosion and the amount of material that falls back – the degenerate remnant of a core collapse is a neutron star. Above this mass, the remnant collapses to form a black hole. The theoretical limiting mass for this type of core collapse scenario is about 40–50 M☉." -- https://en.wikipedia.org/wiki/Type_II_supernova
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First row - supernovas form neutron stars, not black holes. Colliding stars is a circumstance of which I am unaware, but it could happen only if the composite mass of the stars was great enough, and that would have to be many times the mass of our sun.
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