White dwarf

Definition

A white dwarf is a small, dense stellar remnant that forms when a star exhausts its nuclear fuel and expels its outer layers, leaving behind a hot core. These objects are typically composed mainly of carbon and oxygen and are the final evolutionary stage of stars like our Sun. White dwarfs represent a critical phase in the life cycle of stars and play a significant role in the overall structure of galaxies.

5 Must Know Facts For Your Next Test

1. White dwarfs are typically about the size of Earth but contain roughly 60% of the Sun's mass, resulting in incredibly high densities.
2. Once formed, white dwarfs no longer undergo fusion reactions; they gradually cool and fade over billions of years.
3. The Chandrasekhar limit states that a white dwarf cannot exceed approximately 1.4 times the mass of the Sun; if it does, it may collapse into a neutron star or black hole.
4. As white dwarfs cool, they can crystallize into solid carbon structures, leading to the eventual formation of 'diamond stars.'
5. The presence of white dwarfs can influence the evolution of binary star systems, as they can accrete matter from a companion star, potentially leading to phenomena like novae or Type Ia supernovae.

Review Questions

• How does a white dwarf form and what processes lead to its creation during stellar evolution?
  • A white dwarf forms after a star has exhausted its nuclear fuel and has gone through the red giant phase. During this phase, the star sheds its outer layers into space, leaving behind the hot core. This core is primarily composed of carbon and oxygen and represents the final evolutionary state for stars like our Sun. The remnant no longer undergoes fusion reactions but instead slowly cools over time.
• Discuss the significance of the Chandrasekhar limit and its implications for the fate of white dwarfs.
  • The Chandrasekhar limit is crucial because it defines the maximum mass a white dwarf can have before collapsing under its own gravity. If a white dwarf exceeds approximately 1.4 times the mass of the Sun, it cannot support itself against gravitational collapse and may transition into a neutron star or black hole. This limit has significant implications for understanding stellar evolution and the formation of different types of astronomical objects following stellar death.
• Evaluate the role of white dwarfs in binary star systems and their impact on astronomical phenomena.
  • In binary star systems, white dwarfs can interact with their companion stars by accreting material from them. This process can lead to various astronomical phenomena such as novae, where explosive fusion occurs on the surface of the white dwarf, causing sudden brightness. Additionally, if enough mass is accumulated to surpass the Chandrasekhar limit, it may result in a Type Ia supernova, which is an important tool for measuring cosmic distances and understanding the expansion of the universe.

Related terms

red giant:

A red giant is a phase in stellar evolution where a star expands and cools after exhausting the hydrogen in its core, leading to the fusion of heavier elements.

supernova:

A supernova is a powerful and luminous explosion that occurs at the end of a star's life cycle, often resulting in the ejection of the outer layers and leaving behind a neutron star or black hole.

degeneracy pressure: Degeneracy pressure is a quantum mechanical effect that arises when fermions, such as electrons, are packed into a small space, counteracting gravitational collapse in white dwarfs.