White dwarf stars
White dwarfs are compact stellar remnants left after many stars, including the Sun, shed their outer layers. Roughly Earth-sized but containing a substantial fraction of a solar mass, they are supported by electron degeneracy pressure rather than ongoing core fusion. They cool over time and provide important evidence about stellar evolution, binary systems and thermonuclear supernovae.
Formation and properties
A white dwarf is the exposed, compact core of a star that has lost most of its outer layers. Stars in the Sun’s broad mass range can pass through a red-giant phase and expel their envelopes; the remnant core is left behind, sometimes within an expanding planetary nebula. A typical white dwarf has a mass comparable to the Sun’s but a radius only slightly larger than Earth’s, making it extraordinarily dense. White dwarfs are common endpoints of stellar evolution, whereas more massive stellar cores can end as neutron stars or black holes.
What supports a white dwarf?
A white dwarf no longer maintains the ordinary core fusion that powered its former star. Instead, electron degeneracy pressure—arising from quantum mechanics and the Pauli exclusion principle—resists further gravitational compression. In the standard idealized model, this support has an upper mass near 1.4 times the Sun’s mass, known as the Chandrasekhar limit. It is an approximate limit for white-dwarf stability; the later outcome of a particular star depends on its composition and history.
Cooling and observation
After formation, a white dwarf radiates stored heat and gradually cools. It has no sustained core fusion to replenish that energy. Because it is small and faint compared with ordinary stars, many are found through their effects on companions in binary systems or with sensitive observations. Their temperatures, brightnesses and distributions help astronomers study stellar ages and the evolution of stars.
White dwarfs in binary systems
Some white dwarfs orbit another star. In certain binaries, gas can flow from the companion onto the white dwarf, changing its mass and producing high-energy radiation. Accreting white dwarfs near the stability limit can undergo runaway thermonuclear burning; Type Ia supernovae are associated with white-dwarf systems. Astronomers continue to investigate the different routes that lead to these explosions, including accretion from a companion and interactions between two white dwarfs.
Key facts
- Remnant
- The compact core left after a star sheds its outer layers.
- Typical scale
- A white dwarf can contain a substantial fraction of a solar mass within a radius roughly comparable to Earth’s.
- Main support
- Electron degeneracy pressure, not ongoing core fusion.
- Approximate stability limit
- About 1.4 solar masses in the standard model; the precise interpretation depends on physical assumptions.
- Long-term change
- An isolated white dwarf radiates stored heat and cools over time.
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References
- 1.White Dwarfs
NASA Goddard Space Flight Center, Imagine the Universe! · other · reliability: unverified · retrieved 6 November 2026
Supports: Formation from stars like the Sun, approximate size and mass, planetary nebulae, cooling and observational examples.
- 2.White Dwarf Stars
NASA Goddard Space Flight Center, Imagine the Universe! · other · reliability: unverified · retrieved 6 November 2026
Supports: Electron degeneracy pressure, the Pauli exclusion principle, the mass-radius relation and the approximate Chandrasekhar limit.
- 3.Neutron Stars and White Dwarfs
Center for Astrophysics | Harvard & Smithsonian · other · reliability: unverified · retrieved 6 November 2026
Supports: White-dwarf composition, approximate size, evolution, binary mass transfer and Type Ia supernova pathways.
- 4.Pushing White Dwarfs Over the Edge
NASA Goddard Space Flight Center, High Energy Astrophysics Science Archive Research Center (HEASARC) · other · reliability: unverified · retrieved 6 November 2026
Supports: Electron degeneracy support, approximate mass limit, and observations of accreting magnetic white dwarfs in binaries.
- 5.White Dwarf Stars
Annual Review of Astronomy and Astrophysics · other · reliability: unverified · retrieved 6 November 2026
Supports: Peer-reviewed review of observations and properties of white-dwarf stars.
References are suggested by the research engine and may be incomplete. Unverified URLs are omitted rather than guessed.
Article history
- Version 16 November 2026 · EditorCreated by Zapia