Thermalized components/virialized

[ChrisVer]

I am trying to understand what does someone mean when he or she says that a particle component (eg for CDM) is thermalized/virialized in the galactic halo...
What happens during thermalization and what's the difference between virialized/unvirialized components?

Thanks...

 

[PeterDonis]

The Wikipedia page on the virial theorem may help, particularly the section on "in astrophysics".

 

[ChrisVer]

I think that the wiki article is just referring to the fact that matter in galaxies subject to gravitational potential, can have some statistical dispersion in velocities (the sigma), and this is related to the gravitational potential...

However it doesn't make any distinction between thermalized/non-thermalized or virialized/unvirialied or how the transition is being happening...

In case you have some cloud of CDM in the galactic halo, is that cloud virialized or not? If it is not thermalized, how does it get thermalized?

 

[Chalnoth]

The idea is that over time, a galaxy will eventually relax into a state that follows the virial theorem. But when there has been a significant recent disturbance (e.g. a merger between similar-sized galaxies), the galaxy is not well-described by the virial theorem at all.

 

[sardar]

When we talk about thermalized or virialized components in the context of galactic halos, we are referring to how the particles or matter in these regions are moving and interacting with each other. Thermalization refers to the process by which particles reach a state of thermal equilibrium, meaning they have similar energies and velocities. This can occur through collisions and interactions between particles, which cause them to exchange energy and reach a stable distribution.

In a galactic halo, thermalization can occur through various processes such as gravitational interactions, scattering off of other particles, and interactions with radiation. When a component, such as cold dark matter (CDM), is thermalized in the halo, it means that the particles have reached a state of equilibrium and have similar energies and velocities.

On the other hand, virialization refers to the overall gravitational balance between a system of particles. In a galactic halo, this means that the gravitational pull of the dark matter and other components is balanced by the outward pressure from their motions. When a component is virialized, it means that it is gravitationally bound to the system and is in a stable state.

The difference between virialized and unvirialized components is that unvirialized components are not yet in a state of stable equilibrium. This could be because they are still undergoing interactions and collisions with other particles, or they have not yet been affected by the overall gravitational balance of the system.

Overall, understanding the thermalization and virialization of components in galactic halos is crucial for understanding the dynamics and evolution of these systems. It can also provide insight into the properties and behavior of dark matter, which is a major component of these halos.