Cold Dark Matter: Bottom-Up vs. Top-Down Structure Formation

In summary, cold dark matter implies a bottom-up scenario of structure formation, while hot dark matter implies a top-down scenario. This is due to the different damping effects of collisionless particles.
  • #1
blumfeld0
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Why does cold dark matter imply a bottom-up scenario of structure formation? and why does hot dark matter imply a top-down scenario of structure formation?

is it simply because cold dark matter is slow moving (non-relativistic) and slow moving things are more likely to clump together to form larger things because they possesses less energy and momentum? or is there more to it?

thank you in advance!
 
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  • #2
I can't answer your question specifically. However, the various studies of cold vs. warm are made using computer simulations of how the universe would evolve after the big bang and comparing to what is observed.
 
  • #3
This is due to damping of density perturbations. For collisionless particles the most important damping effect is the free streaming damping. Free streaming damping means that the gravitation of the density perturbations of those particles cannot bind them below their free streaming length, and therefore density perturbations smaller than this length cannot form. The free streaming length is the length that those particles can travel until they become non-relativistic. Heavy dark matter particles like CDM particles are assumed to become non-relativistic very early, having thus a small free streaming length. This, in turn, means that density perturbations on small scales can be formed leading to a bottom-up scenario of structure formation.
 
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  • #4
if anyone knows of any papers at any level that i can read to understand free stream damping and its relationship to cold/hot dark matter better, please post them here.

thank you!
 
  • #5
You can find a small introduction in section 7 of the reference 21 (Neutrinos and structure formation in the universe) here:
http://www.ita.uni-heidelberg.de/~msb/Publications/pubConferences.html [Broken]

Here you can find some general notions about the formation of large scale structures:
http://fisica.usac.edu.gt/public/curccaf_proc/borganihtml/borgani.html
 
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  • #6
i will read those. thanks much!
 

1. What is cold dark matter?

Cold dark matter is a type of matter that does not interact with light or other forms of electromagnetic radiation. It is believed to make up about 85% of the total matter in the universe and is responsible for the large-scale structure and dynamics of galaxies and galaxy clusters.

2. What is the bottom-up structure formation theory?

The bottom-up structure formation theory proposes that smaller structures, such as galaxies, form first and then merge over time to create larger structures, such as galaxy clusters. This theory is based on the idea that cold dark matter is more abundant in smaller scales and gradually accumulates to form larger structures.

3. What is the top-down structure formation theory?

The top-down structure formation theory suggests that larger structures, such as galaxy clusters, form first and then break down into smaller structures, such as galaxies. This theory is based on the idea that cold dark matter is more abundant in larger scales and then fragments into smaller structures over time.

4. Which theory is currently supported by evidence?

Both the bottom-up and top-down structure formation theories have some observational evidence to support them. However, the current consensus among scientists is that the bottom-up theory is more in line with observations and is the dominant theory for explaining the formation of large-scale structures in the universe.

5. How does the study of cold dark matter impact our understanding of the universe?

The study of cold dark matter is crucial for understanding the formation and evolution of the universe. It helps explain the large-scale structures we observe, such as galaxies and galaxy clusters, and also plays a significant role in the formation of stars and planetary systems. By studying cold dark matter, scientists can gain a better understanding of the fundamental laws of physics and the origins of our universe.

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