Questions on dark matter and dark energy

In summary: So there's not a single answer to this question, and it's an active area of research. In summary, dark matter appears to be distributed throughout the universe in the same way, and there is no evidence to suggest that it is anything other than normal matter.
  • #1
Phantom13
8
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I have been researching online, but there are many things I am still unsure of because its hard to find the answers to specific questions.

1.) I know how scientists observe dark matter. They can view its gravitational effects. I want to know exactly how it is distributed throughout the universe though. I've heard that it clumps together on the edges of galaxies, but is this true for all galaxies? Can clumps of dark matter be seen out in the vacuum with no proximity to normal matter at all, or are they always attached to "normal" matter?

2.) Does dark matter move with "normal" matter or does it generally stay stationary at one point in the vacuum?

3.) Does it appear to be the same kind of dark matter throughout the entire universe, or do some clumps of the same size appear to have larger gravitational effects than others?

4.) How do scientists observe the effects of dark energy other than seeing that the expansion of the universe is accelerating?
 
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  • #2
Dark matter and dark energy are related by name only, they are distinctively different. We infer the existence of dark matter by its gravitational effects. We have no idea about the properties of DM particles. It does, however, appear to be 'cold' - i.e., generally not moving at relativistic speeds. The existence of DE is inferred strictly from its effect on expansion of the universe.
 
  • #3
Phantom13 said:
I have been researching online, but there are many things I am still unsure of because its hard to find the answers to specific questions.

1.) I know how scientists observe dark matter. They can view its gravitational effects. I want to know exactly how it is distributed throughout the universe though. I've heard that it clumps together on the edges of galaxies, but is this true for all galaxies? Can clumps of dark matter be seen out in the vacuum with no proximity to normal matter at all, or are they always attached to "normal" matter?
In the early universe, normal matter and dark matter tended to attract one another, so that an overabundance of dark matter generally also coincides with an overabundance of normal matter.

The normal matter, however, experiences friction, and so collapses much more than the dark matter, which experiences no friction. So it's not so much that dark matter collects around the edges of galaxies, but that galaxies form in the centers of large blobs of dark matter.

Now, it isn't quite as simple as this, because when stars start to form, things tend to get violent, and a low-mass overdensity will blow out most of the matter shortly after the first stars form, leaving a galaxy with almost nothing but dark matter.

Phantom13 said:
2.) Does dark matter move with "normal" matter or does it generally stay stationary at one point in the vacuum?
Yes, dark matter moves with normal matter. Most of the time. As above: normal matter experiences friction, dark matter does not. Gas clouds tend to collide, while dark matter will pass right through a collision. See this blog post for a neat description:
http://blogs.discovermagazine.com/cosmicvariance/2006/08/21/dark-matter-exists/

Phantom13 said:
3.) Does it appear to be the same kind of dark matter throughout the entire universe, or do some clumps of the same size appear to have larger gravitational effects than others?
There's no evidence of any difference in the makeup of dark matter, and there's no good reason why we would ever expect this.

Phantom13 said:
4.) How do scientists observe the effects of dark energy other than seeing that the expansion of the universe is accelerating?
A smaller but still noticeable effect is on the rate of formation of galaxy clusters. Dark energy tends to make such clusters form more slowly. This effect can be seen in the CMB with what is known as the Integrated Sachs-Wolfe effect, and there are also other studies directly measuring the formation of structure in the universe (such as weak lensing surveys) that are investigating this.
 
  • #4
My big question is whether or not there is a significant (statistically averaged)derivative in redshift with respect to radial distance(δz/δr where z is the redshift). In particular if nearer intergalactic objects(ok, galaxies included :p) have greater or lesser redshift than very distant objects. And by very distant I mean a radial distance r≥ 1,000,000,000 light years.
 
  • #5
Zelyucha said:
My big question is whether or not there is a significant (statistically averaged)derivative in redshift with respect to radial distance(δz/δr where z is the redshift). In particular if nearer intergalactic objects(ok, galaxies included :p) have greater or lesser redshift than very distant objects. And by very distant I mean a radial distance r≥ 1,000,000,000 light years.
Average redshift increases monotonically with distance. Precisely how it increases with distance depends upon the rate of expansion over time, which is not constant, and not terribly simple at longer distances.
 

1. What is dark matter?

Dark matter is a type of matter that makes up about 85% of the total matter in the universe. It does not emit or absorb light, making it invisible to our current telescopes and instruments. Its existence is inferred through its gravitational effects on visible matter.

2. How is dark matter different from regular matter?

Dark matter is different from regular matter in several ways. It does not interact with electromagnetic radiation, so it does not emit or absorb light. It also does not interact with any of the fundamental forces except gravity, making it difficult to detect and study. Additionally, dark matter is thought to be made up of different types of particles than regular matter.

3. What is dark energy?

Dark energy is a mysterious force that is thought to make up around 70% of the total energy in the universe. It is believed to be responsible for the accelerated expansion of the universe and is characterized by its negative pressure, which causes space to expand at an increasing rate.

4. How do scientists study dark matter and dark energy?

Scientists study dark matter and dark energy through various methods, including observing the gravitational effects they have on visible matter, studying the cosmic microwave background radiation, and conducting experiments with particle accelerators. They also use mathematical models and simulations to better understand these elusive substances.

5. What is the current understanding of dark matter and dark energy?

While there is strong evidence for the existence of dark matter and dark energy, their exact nature and properties are still not fully understood. Scientists continue to conduct research and experiments to better understand these substances, and new theories and discoveries are constantly emerging. The study of dark matter and dark energy remains an active and ongoing area of research in astrophysics and cosmology.

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