What’s the largest mass that a neutron star — the dense, collapsed core of a massive star — can grow to before further collapsing into a black hole? Recent gravitational-wave events are providing new insight.
Finding the Maximum
Artist’s impression of a strongly magnetized neutron star. [NASA/Penn State University/Casey Reed]Neutron stars consist almost entirely of neutrons packed together at the density of atomic nuclei. This extreme mass in such a small space results in an extraordinary inward gravitational pull that increases as more neutrons are packed in. When the crushing gravitational force exceeds the combined quantum and nuclear forces pushing outward, the star collapses to form a black hole.
What is the maximum mass limit above which a neutron star collapses? Theory suggests that, for a non-rotating neutron star, it’s somewhere around 2 or 3 times the mass of the Sun — but the precise value relies on the unknown state of matter inside the neutron star. To get around this missing information, we need observational constraints to help us pin down how heavy a neutron star can be.
In recent years, gravitational waves have provided valuable new insight. Two particular mergers of compact objects have tempted us ...