Keplerian disk

Definition

A Keplerian disk is a type of accretion disk where the material in the disk orbits a central mass under the influence of gravity, following Kepler's laws of planetary motion. In these disks, the orbital speed of the material varies with its distance from the central object, leading to a specific structure and behavior that is crucial for understanding phenomena like star formation and black hole accretion.

5 Must Know Facts For Your Next Test

1. In a Keplerian disk, objects further from the central mass move slower than those closer to it, as dictated by Kepler's third law.
2. The temperature and density of the disk can vary significantly with distance from the central mass, affecting the types of processes that can occur within the disk.
3. Viscous forces in the disk enable angular momentum transfer, allowing material from outer regions to spiral inward toward the central mass.
4. Keplerian disks are commonly observed in systems such as young stellar objects and binary star systems, providing insights into star formation and evolution.
5. Instabilities can arise within Keplerian disks, leading to phenomena such as spiral arms or clumps of matter that can eventually form new stars or planets.

Review Questions

• How does a Keplerian disk illustrate Kepler's laws of planetary motion in its structure?
  • A Keplerian disk showcases Kepler's laws by demonstrating that materials orbiting a central mass do so with varying speeds based on their distance from that mass. According to Kepler's third law, planets further from the sun travel slower than those closer to it. This principle extends to all objects in a Keplerian disk, where those nearer to the center exhibit higher orbital speeds, leading to a structured and dynamic environment.
• What role does angular momentum play in the dynamics of a Keplerian disk, and how does it affect the flow of material within the disk?
  • Angular momentum is crucial in a Keplerian disk because it dictates how material moves in relation to the central mass. As material spirals inward, it loses gravitational potential energy and transfers angular momentum outward. This process allows for a steady flow of material from the outer regions towards the inner regions of the disk, while maintaining overall stability and facilitating processes like star formation.
• Evaluate the significance of viscous forces in maintaining the structure and evolution of a Keplerian disk over time.
  • Viscous forces are essential for sustaining the structure and evolution of a Keplerian disk by enabling angular momentum transfer between different parts of the disk. These forces cause material to move inward while allowing other materials further out to migrate outward. This exchange plays a vital role in regulating temperature and density within the disk, impacting phenomena such as star formation and stability against instabilities that could disrupt its overall configuration.

Related terms

Accretion disk: A rotating disk of matter formed by the gravitational attraction of a central object, where material spirals inward, losing energy and angular momentum.

Angular momentum: A physical quantity that represents the rotational motion of an object; in a Keplerian disk, it is conserved as material moves in orbits around the central mass.

Gravitational potential energy: The energy an object possesses due to its position in a gravitational field; in a Keplerian disk, this energy influences the dynamics and stability of the orbiting material.