Common envelope phase

Definition

The common envelope phase is a stage in the evolution of binary star systems where one star engulfs the outer layers of its companion, leading to the formation of a shared envelope of gas around both stars. This phase is critical as it significantly alters the dynamics and evolutionary paths of the binary system, often resulting in close binary systems, neutron stars, or black holes after further evolution.

5 Must Know Facts For Your Next Test

1. The common envelope phase can lead to significant orbital shrinkage due to the loss of angular momentum as one star loses mass to its companion.
2. During this phase, energy is released as the envelope contracts and becomes heated, which can lead to various outcomes including the formation of compact objects.
3. The common envelope phase is thought to play a crucial role in the formation of binary neutron stars and black hole binaries.
4. The outcome of the common envelope phase largely depends on the initial masses of the stars involved and their mass ratios.
5. The theoretical models suggest that many close binaries we observe today may have undergone a common envelope phase in their past.

Review Questions

• How does the common envelope phase influence the future evolution of a binary star system?
  • The common envelope phase significantly influences the future evolution of a binary star system by altering its mass distribution and orbital dynamics. When one star engulfs its companion's outer layers, it leads to a shared envelope that can result in increased mass transfer and enhanced gravitational interactions. This often causes the orbit to shrink, eventually leading to phenomena such as the formation of neutron stars or black holes, depending on the masses involved.
• What are the potential outcomes for binary systems that undergo the common envelope phase, and how do these outcomes vary with different initial conditions?
  • The potential outcomes for binary systems that undergo the common envelope phase include the creation of close binaries, neutron stars, or black holes. These outcomes are influenced by several factors such as the initial masses of each star, their separation distance, and how much mass is transferred during this phase. If one star is significantly more massive than its companion, it may lead to different evolutionary pathways compared to systems with more equal masses.
• Evaluate the importance of understanding the common envelope phase in relation to observing transient astronomical events like Type Ia supernovae.
  • Understanding the common envelope phase is crucial for evaluating transient astronomical events like Type Ia supernovae because it provides insights into how these explosive events occur in close binary systems. The interactions during this phase can lead to scenarios where a white dwarf accumulates enough mass from its companion to reach critical conditions for ignition. By studying this phase, astronomers can better predict when and how such supernovae will occur, thus enhancing our understanding of cosmic evolution and distance measurement in the universe.

Related terms

Roche Lobe:

The region around a star in a binary system within which orbiting material is gravitationally bound to that star, impacting mass transfer during the common envelope phase.

Mass Transfer: The process by which one star in a binary system transfers mass to its companion, often occurring during the common envelope phase and affecting their future evolution.

Post-common Envelope Binary: A binary system that has emerged from the common envelope phase, characterized by a close separation between the two stars and often leading to phenomena such as Type Ia supernovae.