Can We Now Predict When A Neutron Star Will Give Birth To A Black Hole?

"If the star is nonrotating, then this mass is not too difficult to compute and is called the maximum nonrotating mass, or M_TOV. However, this is not the largest mass possible because if the star is rotating, it can sustain more mass than if is not rotating. Even in this case, however, there is a limit because there is a limit to how much a star can rotate before being broken apart from the centrifugal force. Hence, the absolute largest mass that a neutron star can achieve is known as the "maximum mass of a maximally rotating configuration", M_max.  This is the largest possible mass of the most rapidly rotating model. Suppose you have built such a model: if you added a single atom onto it, it would collapse to a black hole, while it would break apart if you spun it a bit more."

"What made it difficult in the past to calculate M_max is its value will differ from what composes the neutron star (i.e. its "equation of state") and this is something we don't really know. Neutron-star matter is so different from the one we know that we can only make educated guesses; and unfortunately, there are many guesses because there are several different ways to compute the properties of the equation of state. So one ended up up with a situation in which not only the maximum mass was different for different equations of state, but even the maximum rotation speed was different for different equations of state."

"Universal relations simply state that objects that are apparently different actually share many things in common. For example, although we are different from other mammals, say pigs, our genome has a huge amount of common features, essentially because we have to synthesize the same proteins, breath the same air, etc. Hence, if we learn of hemoglobin actually works for one mammal, we have learned for many more mammals. This seems to happen also for neutron stars so that although there are many equations of state that predict different results for M_max, they all show there is a universal relation between M_max and M_TOV. More specifically, we have found that M_max = (1.203 +- 0.022) M_TOV."