Neutron Star Density Calculator

Neutron stars are the collapsed cores of massive stars that exploded as supernovae. They are among the densest objects in the universe — only black holes are more compact.

Average density:

ρ = M / (4/3 × π × R³)

Surface gravity:

g = GM / R²

Escape velocity:

v_esc = √(2GM / R)

Typical neutron star:

• Mass: 1.4 M☉ = 2.8 × 10³⁰ kg (most measured neutron stars cluster near 1.4 M☉)
• Radius: ~10 km (about the size of a city)
• Average density: ~7 × 10¹⁷ kg/m³ (3× nuclear density)
• Surface gravity: ~2 × 10¹² m/s² (200 billion times Earth’s gravity)
• Escape velocity: ~176,000–193,000 km/s, which is 59% to 64% of the speed of light. Closer to two-thirds of light speed than to half, and the exact figure depends heavily on the radius, which is the least well known of a neutron star’s properties

Nuclear density (saturation density): ρ₀ = 2.3 × 10¹⁷ kg/m³ The core of a neutron star exceeds several times nuclear density. At these densities, matter may exist as strange quark matter, hyperons, or other exotic states.

Pulsars: Many neutron stars are observed as pulsars — rotating with periods from milliseconds to seconds, emitting beams of radio waves like a lighthouse. The fastest known pulsar (PSR J1748-2446ad) spins at 716 times per second. At its equator, the surface moves at about 24% of the speed of light.

Maximum mass: The Tolman-Oppenheimer-Volkoff limit is roughly 2.0–2.5 M☉. Above this, neutron degeneracy pressure plus the repulsive part of the strong nuclear force can no longer hold the star up, and it collapses to a black hole. Do not confuse this with the Chandrasekhar limit of about 1.4 solar masses: that one is where electron degeneracy fails and a white dwarf gives way. Different particle, different pressure, different mass.