When can globular clusters be considered collisionless?

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Discussion Overview

The discussion centers on the conditions under which globular clusters can be considered collisionless for the purpose of using specific software designed for collisionless dynamics. Participants explore the implications of this classification in relation to the properties of globular clusters, such as luminosity and velocity dispersion, and seek recommendations for suitable software that can operate on a single high-performance PC.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant expresses interest in using collisionless dynamics software for globular clusters, questioning the validity of this approach given the collisional nature of these clusters, especially in their inner regions.
  • Another participant mentions using NMODY for the globular cluster NGC 2419, arguing that it is appropriate due to the long relaxation time of that cluster, which exceeds the Hubble time.
  • There is a request for clarification on what conditions would make the use of collisionless software appropriate for a broader range of Galactic globular clusters.
  • A participant questions the terminology used, suggesting that "legal" may be misleading and asks for clarification on the conditions under which the software would yield valid results.
  • The original poster clarifies that "legal" refers to adherence to scientific principles and not violating fundamental laws, such as conservation of momentum.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the conditions under which globular clusters can be considered collisionless, and there is some confusion regarding terminology. Multiple viewpoints regarding the appropriateness of using collisionless dynamics software remain present.

Contextual Notes

Participants express uncertainty regarding the specific conditions that would allow for the classification of globular clusters as collisionless, indicating a need for further exploration of the topic.

kderakhshani
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Hi all.

I'd like to use a software package, that has been designed for collisionless dynamics, to investigate general globular clusters. As they are highly collisional, at least in their inner parts, this perhaps makes no sense.

However, it may be meaningful for some time- or length-scales or to obtain their global properties, such as luminosity, velocity dispersion, etc.

Do you have any idea?

If that is anyway illegal, what software do you suggest that can be run on a single high-performance PC?
( I mean without having PC clusters, GPUs, GRAPE, supercomputers, etc.)

Thanks a lot.
 
Astronomy news on Phys.org
Are you asking us to suggest a software package to you?
 
The code I used for some globular cluster (NGC 2419) was NMODY, which had been written for COLLISIONLESS stellar systems. For NGC 2419 it is legal, cause its relaxation time is very long (longer than the Hubble time). (K.Derakhshani, ApJ, 783, 48, 2014)

Now, I want to use it (or some other collisionless code) for the total range of Galactic globular clusters.

Under what conditions (if any) will this be legal?

If none, what other software do you suggest to me that can be run on a single PC?

Thanks.
 
kderakhshani said:
Under what conditions (if any) will this be legal?

Your word use here is slightly confusing. 'Legal' usually means that something isn't against the law or rules. Are you asking under what conditions this software would be appropriate to use and give good results?
 
@Drakkith
Thank you for your comment.
In a wider prospect "legal" means "concordance with the rules of the game". In scientific workss it stands for "not violating the discipline, some scientific law, etc.". For example, if something violates the LAW of conservation of linear momentum, it will be "ILLEGAL".

Anyway, you got it. Do you have any answer to my question?
Thanks
 

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