Does galaxy formation conserve mass and angular momentum?

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Discussion Overview

The discussion revolves around the conservation of mass and angular momentum during the formation of galaxies from collapsing gas clouds. Participants explore theoretical implications, equations, and the physical processes involved in galaxy formation, including the role of angular momentum and mass ejection.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the original gas cloud and the resulting galaxy may have similar or significantly different total mass and angular momentum, raising questions about the validity of equations used to describe this process.
  • Others argue that while individual particles may change their momentum, the total angular momentum of a closed system is conserved, as per Newton's Third Law.
  • A later reply questions whether a collapsing gas cloud can eject mass, which could affect the conservation of angular momentum, suggesting that if mass is ejected, the resulting galaxy could have different angular momentum than the original cloud.
  • Some participants highlight that the initial gas cloud does not behave like a galaxy and that the dynamics of collapsing gas clouds may not conform to simple circular orbit assumptions.
  • There is a discussion about whether Newtonian mechanics apply to galaxy formation, with some suggesting that General Relativity may be necessary to fully understand the processes involved.
  • One participant mentions that the net angular momentum of the initial dust cloud is conserved, with collisions between particles potentially canceling out some angular momentum, leading to the formation of a dust disc around a proto-star.
  • Another participant asserts that it is valid to discuss the total angular momentum of both the gas cloud and the galaxy, emphasizing that angular momentum is conserved during the transition from one state to the other.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the conservation of mass and angular momentum in galaxy formation, and the discussion remains unresolved with no consensus on the specifics of the processes involved.

Contextual Notes

There are limitations in the discussion regarding assumptions about the behavior of gas clouds, the applicability of Newtonian mechanics versus General Relativity, and the potential for mass ejection during the formation process.

  • #31
And I was hoping I could just say... L = m.r.v... a-ha, I caught you! :D... I'm wiser now
 
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  • #32
fbs7 said:
(e) The whole thing is relativistic, so these are not easy equations
Relativistic effects should be negligible.
 

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