The existence of spacetime singularities in Einstein's theory of General Relativity has long troubled physicists. Now, a new theory of gravitation is able to reproduce all the classical tests of relativity, while avoiding singularities such as the Big Bang or those inside black holes. These results, co-authored by Paolo Pani, Vitor Cardoso and Térence Delsate, are being published by the prestigious Physical Review Letters.

Subramanyan Chandrasekhar was a young researcher when, at the age of 19, he proposed that very massive stars, after exhausting their fuel, would not be able to support themselves against gravity and would collapse. As a result a black hole would eventually form and a singularity, a point in spacetime where the classical laws of physics break down, would develop in its interior. Sir Arthur Eddington was a fierce opponent of this idea, "there should be a law of Nature to prevent a star from behaving in this absurd way!", he once claimed.

In the many decades since the dispute with Eddington, Chandrasekhar's ideas prevailed and gave rise to a beautiful theory of compact stars and black holes. Nevertheless, echoes of Eddington's arguments persist in the existence of singularities and physicists found this so hideous that in 1969 Sir Roger Penrose proposed his famous Cosmic Censorship Conjecture to save classical General Relativity.

In an article to be published in Physical Review Letters, Paolo Pani, Vitor Cardoso and Térence Delsate, three scientists from IST (Portugal), have demonstrated that a new theory of gravity does not show any of these undesirable features. As they show, in this intriguing theory singularities are not necessarily the outcome of gravitational collapse because, at ultra-high densities, a new "repulsive gravitational force" appears. As a bonus, the theory also predicts the existence of "dark matter stars", compact stars which are invisible to telescopes, but contribute to the dark matter content of our Galaxy.

Oddly enough, this new theory goes back to an idea proposed in 1924...by Eddington!