Dark energy and the rotation curve of spiral galaxies

In summary, the rotation curve of spiral galaxies suggests that the mass of stars is proportional to their distance from the central core, rather than following the expected 1/√r pattern. There is no direct evidence for the existence of dark energy, which is a separate concept from dark matter. However, observations such as gravitational lensing and the Bullet cluster support the dark matter hypothesis. Recent discoveries of galaxies with little to no dark matter also provide evidence for this model. Alternative explanations, such as modified gravity theories, do not account for all observations.
  • #1
Apashanka
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Recently I have studied that from the rotation curve of spiral galaxies, the nearly constt. behaviour of velocity of the stars situated far away from the central core suggests mass(r) ~ r ,rather than 1/√r as expected.
Are there any other theory which proves the existence of dark energy ??
 
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  • #2
Dark matter is the proposed explanation for galaxy rotation curves. Dark energy is the name given to what is driving the apparent accelerated expansion of the universe. These are two separate things and their only relationship is the word "dark" in their titles.

There are a number of observations that support the dark matter hypothesis. Gravitational lensing shows light bending around galaxies in a manner consistent with that model. The Bullet cluster observation shows us the result of two galaxy clusters colliding. It includes a region where we measure gravitational lensing, but no visible matter to cause it. This is consistent with dark matter being "knocked loose" during the collision.
Recently there have been discoveries of galaxies that behave as if they have little to no dark matter. This is, in fact, evidence supporting the dark matter model.( With other explanations for galaxy rotation curves, such as modified gravity theories, One would expect to see the effect in all galaxies, where as there is nothing that says that every galaxy must have dark matter.
 

1. What is dark energy?

Dark energy is a hypothetical form of energy that is thought to make up about 70% of the total mass-energy of the universe. It is believed to be responsible for the observed accelerated expansion of the universe.

2. How does dark energy affect the rotation curve of spiral galaxies?

Dark energy does not directly affect the rotation curve of spiral galaxies. However, its presence in the universe does influence the overall expansion rate of the universe, which in turn affects the gravitational pull on galaxies and their rotation curves.

3. What is the rotation curve of a spiral galaxy?

The rotation curve of a spiral galaxy is a graph that shows the relationship between the orbital velocity of stars or gas clouds in the galaxy and their distance from the center. It is typically flat, indicating that the orbital velocity remains constant as distance from the center increases.

4. How does the rotation curve of a spiral galaxy provide evidence for dark energy?

The flatness of the rotation curve of spiral galaxies is unexpected based on the observed distribution of visible matter in the galaxy. This suggests that there must be an unseen source of mass, such as dark matter or dark energy, that is contributing to the gravitational pull and keeping the rotation curve flat.

5. Can dark energy be detected or measured?

Currently, dark energy cannot be directly detected or measured. Its existence is inferred from observations of the accelerated expansion of the universe and its effects on the rotation curves of galaxies. Scientists are still working to understand the nature of dark energy and develop ways to detect and measure it.

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