From the December 2017 issue

How many solar masses must a star be to end up a black hole (before normal mass loss during its life)?

Bill Dellinges Apache Junction, Arizona
By | Published: December 4, 2017
The Homunculus Nebula surrounds the Eta Carinae star system. Eta Carinae contains at least two stars with masses estimated at 90 and 30 times the mass of the Sun. These stars are expected to explode as supernovae in the next few million years, and are massive enough to possibly leave black holes behind.
ESA/Hubble and NASA
Shortly after Albert Einstein came up with his general theory of relativity, Karl Schwarzschild derived its first analytic solution for a point mass. In 1939, Robert Oppenheimer and his graduate student Hartland Snyder wrote a paper that demonstrated how a star might collapse to a point such that not even light could escape from it. The paper was barely noticed, however, until the 1960s, when astrophysicists started searching for such extreme objects and John Wheeler came up with their name: “black holes.”

The latest computer simulations predict that stars more massive than 20 solar masses could end their life by an implosion to a black hole. Once their nuclear fuel is consumed, the sheer weight of these stars crushes them due to their self-gravity. The probability of black hole formation changes with stellar mass. Current models predict a 40 percent probability of black hole formation at around 20 solar masses. These models indicate that the probability of black hole formation could then either vanish or rise to 100 percent around 60 solar masses. But these are all theoretical predictions. Observers are searching for massive stars that disappear in high-resolution images of nearby galaxies, in an attempt to calibrate empirically the black hole formation probability for different progenitor stars.

Avi Loeb
Founding Director of the Black Hole Initiative, Harvard University, Cambridge, Massachusetts