|Chaisson, Eric. Astronomy Today. Englewood, NJ: Prentice Hall, 1993: 503||"beyond 3 solar masses, not even tightly packed neutrons can withstand the star's gravitational pull"||3 solar masses|
|Black Hole -- Encarta Encyclopedia Article. Encarta Online.||"If the core mass exceeds about 1.7 solar masses, collapse to a black hole follows."||1.7 solar masses
|Ebbighausen, E. Astronomy. 5th ed. Toronto: Merill, 1985: 133-134.||"a mass of at least a few solar masses"||3 solar masses|
|Asimov, Isaac. The Story of Black Holes. New York: Walker, 1977: 126.||"It appears that the crucial turning point is 3.2 times the sun's mass… no neutron star can be more than 3.2 times the sun's mass without collapsing further."||3.2 solar masses|
|How Black Holes and Neutron Stars Form. Black Holes and Neutron Stars. Christopher Miller.||"And a star with mass greater than 3 times the Sun's gets crushed into a single point, which we call a black hole"||3 solar masses|
The term "black hole"is of recent origins. It was first informally used in 1967 by John Wheeler to identify collapsed stars. The terminology "frozen star"and "collapsar" was used in reference to black holes prior to 1968.
Black holes are theoretical objects of extreme density and posses gravitational fields so strong that nothing can escape from them. The black hole concept was pioneered by German astronomer Karl Schwarzchild based upon Einstein's theory of relativity. Recently, the existence of black holes was strengthened by the discovery of an object of approximately 3 billion solar masses at the center of the galaxy M87.
The current hypothesis is that black holes form from the inward collapse of a neutron star. Based upon this premise, black holes are brought into being when a neutron star's mass exceeds a certain critical value. Even though there is not a universally accepted critical value, most technical sources indicate the critical value is greater than 3.2 solar masses. A neutron star is the apex on the celestial chain of evolution, and posses no less than 1.5 and no more than 3.2 solar masses. A star less than 1.5 solar masses is referred to as a white dwarf. Isaac Asimov noted that the failure of the nuclear force would result in a chain reaction, leaving nothing remaining to counteract gravitational forces and the neutron star would remain in an indefinite collapse, with it's volume steadily approaching zero and it's surface gravity nearing infinity.
Therefore, in theory, any neutron star whose mass exceeds 3.2 solar masses will collapse and create a black hole. This is due to the tightly packed neutrons that can no longer withstand the star's immense gravitational pull and collapse further.
Jared R. Jagdeo -- 1998