A dying star does not have “weight” in the traditional sense, as weight is a measure of gravitational force that changes based on location. Instead, astronomers measure a star’s mass, which is the amount of matter it contains and remains constant throughout the cosmos. This mass is typically expressed in solar masses (\(M_{\odot}\)), a unit equal to the mass of our Sun. The final mass of a star—the mass it settles into after its death—is a fundamental characteristic in astrophysics. This ultimate mass determines whether the star concludes its life as a white dwarf, a neutron star, or a black hole.
The Pre-Remnant Phase and Mass Shedding
The mass of the final stellar remnant is significantly less than the star’s initial mass due to intense mass loss during the final stages of stellar evolution. Stars approaching their end enter the red giant or red supergiant phase, where their outer layers swell and cool dramatically. This expansion is accompanied by powerful stellar winds, which steadily blow vast amounts of material away from the star’s surface.
For stars similar in mass to the Sun, this mass loss is relatively gentle, creating an expanding shell of gas and dust known as a planetary nebula. The initial star might shed over half its total mass, leaving behind only the dense, hot core. For much more massive stars, the mass loss is far more intense and catastrophic, often involving violent, episodic ejections of material.
The final mass of the core—the material that will become the remnant—is what determines the star’s fate. Stars that begin with up to approximately eight solar masses lose enough outer material to form a lower-mass core. More massive stars retain enough core mass to undergo a violent supernova explosion. This mass-shedding phase dictates which of the three possible stellar corpses will be left behind.
Mass Range of White Dwarfs
White dwarfs are the least massive stellar remnants, formed from the cores of low to intermediate mass stars. They are characterized by a precise upper mass limit known as the Chandrasekhar limit. This boundary is approximately \(1.4\) times the mass of the Sun (\(1.4 M_{\odot}\)) and represents the maximum mass a white dwarf can possess while remaining stable.
Stability is maintained by electron degeneracy pressure, a quantum-mechanical effect where electrons resist being squeezed into the same quantum state. This pressure counteracts the relentless inward pull of gravity. If the core’s mass is below the Chandrasekhar limit, the pressure is sufficient to halt gravitational collapse, leaving behind a stable white dwarf.
If a white dwarf in a binary system accretes matter, its mass can gradually approach this limit. Should the mass exceed \(1.4 M_{\odot}\), the electron degeneracy pressure fails, and the star collapses further. This collapse typically triggers a runaway nuclear fusion reaction resulting in a Type Ia supernova. Some observations suggest that rapidly rotating white dwarfs can briefly sustain a mass up to about \(2.5 M_{\odot}\) before collapse, challenging the conventional limit.
Mass Range of Neutron Stars
A core remnant that exceeds the Chandrasekhar limit continues to collapse, leading to the formation of a neutron star. This typically occurs when a massive star, originally greater than eight solar masses, undergoes a core-collapse (Type II) supernova. Gravitational force overcomes electron degeneracy pressure, forcing electrons and protons to combine into neutrons through inverse beta decay.
The resulting core is supported by neutron degeneracy pressure, where the densely packed neutrons resist further compression. The stable mass range for a neutron star begins just above the Chandrasekhar limit, usually around \(1.4 M_{\odot}\). Its upper boundary is the Tolman-Oppenheimer-Volkoff (TOV) limit, which is the maximum mass that neutron degeneracy pressure can withstand.
The exact value of the TOV limit remains a subject of ongoing research because it depends on the physics of matter at extreme densities. Theoretical estimates for this upper boundary generally fall between \(2.1\) and \(3.0 M_{\odot}\). Recent observations from gravitational wave events suggest the maximum mass for a non-rotating neutron star is closer to \(2.17 M_{\odot}\).
Mass Range of Black Holes
The most massive remnants formed from stellar death are stellar-mass black holes. These objects form if the collapsing core of a massive star exceeds the TOV limit, meaning the mass is greater than approximately \(3.0 M_{\odot}\). At this extreme density, even neutron degeneracy pressure is insufficient to counteract the overwhelming force of gravity.
When the remnant mass surpasses this threshold, the collapse proceeds unimpeded, and the matter is crushed into a singularity. The resulting object is a stellar-mass black hole, whose lower mass boundary is set by the maximum mass of a neutron star. The smallest stellar black holes observed have masses around \(3.3 M_{\odot}\), confirming the theoretical barrier separating neutron stars from black holes.
Unlike white dwarfs and neutron stars, black holes have no known upper mass limit and can continue to grow indefinitely by consuming surrounding matter. While stellar-mass black holes begin their existence above the \(3 M_{\odot}\) threshold, they can eventually reach masses tens of times that of the Sun.