Not all stars become black holes

In 2011, a scientific article raised the exciting but problematic possibility that the formation of black holes could happen more simply than anticipated. Until then, the scientific community was of the opinion that only very massive stars at the end of their lives could become black holes. These circumstances would allow for a sufficiently large amount of matter, confined in a space small enough for it to form. Hirotada Okawa, Vitor Cardoso and Paolo Pani, from the Multidisciplinary Center for Astrophysics (CENTRA) at the Instituto Superior Técnico, have revisited and updated the contours of this problem. The results of their study will be published in the journal Physical Review D e highlight the prevailing view: black holes are extremely rare in our universe.

The article published by two Polish scientists in 2011 suggested that black holes form in anti-de Sitter spacetime, regardless of the initial conditions. The anti-de Sitter spacetime is the simplest solution to Einstein's equations of general relativity. Polish researchers have shown that anti-de Sitter spacetime can act like an open box with a mirrored interior. The reflection of matter inside the box could thus create a point where the density is infinite and form a black hole.

Using their Baltasar Seven Suns supercomputer, the CENTRA researchers ran a set of simulations to solve Einstein's equations and determine whether these 'boxes' exist in the real Universe. The research group concluded that in the Universe the 'boxes' would allow the dissipation of energy and that in the case of less massive objects, such as our Sun, the dissipated energy would be sufficient to block the formation of a point with infinite density. Paolo Pani, an FCT researcher selected in the 2013 Call sums up the results: "We discovered that in realistic cases the collapse of matter can occur, but it's not that easy."

Vitor Cardoso adds that the future of a star is not necessarily to become a black hole - "Gravity doesn't always win!"