For a long time astronomers have puzzled over the lack of observations of compact objects with masses ranging from 2.5 up to 5 solar masses. This mysterious grey area is known as the ‘mass gap’: a range of masses apparently too light for a black hole and too heavy for a neutron star. Both neutron stars and black holes form when very massive stars run out of their nuclear fuel and explode as supernovae. What is left depends on how much of the star’s core remains. The lighter cores tend to form neutron stars, while the heavier ones collapse into black holes. Understanding whether a mass gap exists in the mentioned range, and why, has been a long-lasting puzzle for scientists.
Now, the scientific collaborations running the Advanced Virgo detector at the European Gravitational Observatory (EGO), near Pisa in Italy, and the two Advanced LIGOs, in the US, have announced the discovery of an object of about 2.6 solar masses, i.e. within the so called ‘mass gap’, thus questioning its very existence. For more information visit the EGO (European Gravitational Observatory) site.