Eddington Luminosity

Definition

Eddington luminosity is the maximum luminosity that a celestial object, such as a star or accreting black hole, can achieve when there is a balance between the outward radiation pressure and the inward gravitational pull. This concept is crucial in understanding how massive stars evolve and the limits on accretion rates in astrophysical systems, particularly in the context of accretion disks.

5 Must Know Facts For Your Next Test

1. Eddington luminosity can be expressed with the formula: $$L_{E} = \frac{4\pi GMc}{\kappa}$$, where $G$ is the gravitational constant, $M$ is the mass of the object, $c$ is the speed of light, and $\kappa$ is the opacity of the material.
2. For a typical star like our Sun, the Eddington luminosity is approximately 1.3 x 10^{38} watts.
3. When a celestial object's luminosity exceeds its Eddington limit, it can lead to significant mass loss as radiation pressure overwhelms gravitational attraction.
4. In accretion disks around black holes, reaching Eddington luminosity indicates the maximum rate at which matter can fall into the black hole without being blown away by radiation.
5. Understanding Eddington luminosity is important for studying massive stars and their life cycles, as it helps predict how they will evolve and their eventual fate.

Review Questions

• How does Eddington luminosity relate to the stability of accretion disks around black holes?
  • Eddington luminosity sets a critical threshold for accretion disks, indicating the maximum luminosity achievable before radiation pressure becomes dominant. If an accreting black hole's luminosity exceeds this limit, it can lead to an outflow of material from the disk, destabilizing its structure. This balance between gravitational attraction and radiation pressure is essential for maintaining stable conditions in the disk.
• Discuss the implications of exceeding Eddington luminosity for massive stars during their evolution.
  • Exceeding Eddington luminosity has significant implications for massive stars as it can lead to enhanced mass loss through stellar winds or radiation-driven outflows. This means that if a star surpasses this limit during its lifecycle, it may shed a considerable portion of its mass. As a result, this process influences stellar evolution, potentially affecting the formation of supernovae and other end-of-life phenomena.
• Evaluate how understanding Eddington luminosity contributes to our knowledge of black hole growth and galaxy formation.
  • Understanding Eddington luminosity provides critical insights into black hole growth and the feedback mechanisms influencing galaxy formation. By determining how much matter can be accreted without being expelled due to radiation pressure, we gain a clearer picture of how rapidly supermassive black holes can grow. This knowledge helps astronomers model galactic evolution and understand how energy output from these black holes affects star formation rates in their host galaxies.

Related terms

Radiation Pressure: The pressure exerted by electromagnetic radiation on surfaces, which can counteract gravitational forces in massive objects.

Accretion Disk: A structure formed by diffused material in orbital motion around a central body, often seen in systems where matter is falling into a black hole or neutron star.

Black Hole: A region of spacetime exhibiting gravitational acceleration so strong that nothing can escape from it, not even light, and often associated with high-energy processes like accretion.