A new study from the HUN-REN Wigner Research Centre for Physics in Hungary claims to have pinned down the maximum mass a neutron star can reach before collapsing into a black hole. The team argues the threshold lies between 2.2 and 2.3 times the mass of the Sun — a range that has remained elusive despite decades of astrophysical inquiry.
Neutron stars represent some of the densest objects in the universe, compressing up to two solar masses into a city-sized sphere. A single teaspoon of their material would weigh billions of tons. This new work narrows the long-debated boundary where gravity overwhelms the quantum mechanical forces holding the star together.
The researchers' model uses theoretical calculations rather than direct observation, examining how nuclear matter behaves under extreme pressure. They determined that beyond the 2.2–2.3 solar mass range, even the repulsive forces among neutrons cannot halt gravitational collapse, forcing the object into a black hole.
This finding carries significant implications for gravitational wave astronomy and stellar evolution models. When astronomers detect neutron star mergers via gravitational waves, the remnant's mass could determine whether a larger neutron star or a black hole forms. The paper offers a clear cut-off for that classification process.
The team's result, however, relies on assumptions about the equation of state for dense nuclear matter — a parameter that remains uncertain without direct experimental verification. Future neutron star observations from instruments like the James Webb Space Telescope or next-generation gravitational wave detectors will be needed to test this proposed limit.