Eddington Limit

Definition

The Eddington Limit is the maximum luminosity a star or an accreting black hole can achieve when the outward pressure of radiation balances the inward pull of gravity. This limit is crucial in understanding how massive objects, such as black holes and active galactic nuclei, can grow and evolve. When a system exceeds this limit, radiation pressure can blow away the surrounding material, affecting accretion processes and the characteristics of active galactic nuclei.

5 Must Know Facts For Your Next Test

1. The Eddington Limit can be mathematically expressed as $$L_{E} = \frac{4\pi GMc}{\kappa}$$, 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 black holes, if their luminosity exceeds the Eddington Limit, they can lose mass as radiation pressure pushes material away, which impacts their growth.
3. The Eddington Limit is significant for massive stars as it determines their maximum size; stars larger than this limit may undergo rapid mass loss due to stellar winds.
4. Active galactic nuclei (AGN) are often thought to operate near or at the Eddington Limit, leading to powerful outflows that can influence galaxy evolution.
5. Understanding the Eddington Limit helps astronomers model various astrophysical phenomena, including star formation rates and the growth of supermassive black holes in the universe.

Review Questions

• How does the Eddington Limit influence the growth and stability of massive stars and black holes?
  • The Eddington Limit acts as a threshold for luminosity that massive stars and black holes cannot exceed without facing consequences. For massive stars, exceeding this limit leads to significant mass loss via stellar winds, which limits their growth. In the case of black holes, surpassing this limit results in strong radiation pressure that can expel surrounding material, inhibiting further accretion and influencing their overall mass evolution.
• What role does radiation pressure play in relation to the Eddington Limit for active galactic nuclei?
  • Radiation pressure is a key factor at play when discussing the Eddington Limit for active galactic nuclei. When these luminous regions around supermassive black holes exceed the limit, radiation pressure becomes strong enough to expel gas and dust from their vicinity. This outflow not only impacts the growth of the black hole but also plays a critical role in regulating star formation within the host galaxy, leading to important feedback processes in galaxy evolution.
• Evaluate how understanding the Eddington Limit aids astronomers in studying galaxy evolution and black hole growth across cosmic time.
  • Understanding the Eddington Limit provides astronomers with vital insights into how massive stars and black holes interact with their environments over cosmic time. It helps model star formation rates by explaining how luminosity limits influence mass loss in stars. For supermassive black holes at the centers of galaxies, knowing about this limit enables researchers to comprehend their growth mechanisms and how they affect surrounding matter. Ultimately, this understanding contributes to a broader picture of galaxy evolution, including how feedback processes shape stellar populations and chemical enrichment in galaxies throughout history.

Related terms

Luminosity: The total amount of energy emitted by a star or astronomical object per unit time, usually measured in watts.

Accretion Disk: A structure formed by diffused material in orbital motion around a central body, often associated with black holes and neutron stars, where matter spirals in and releases energy.

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