Dark Energy contribution to plasma temperature in galaxy clusters?

In summary, the study of dark energy's contribution to plasma temperature in galaxy clusters suggests that dark energy may play a significant role in influencing the thermal dynamics of the intracluster medium. By examining the interactions between dark energy and the plasma, researchers aim to understand how dark energy affects the temperature distribution and behavior of gas within clusters, potentially providing insights into the large-scale structure of the universe and the nature of dark energy itself.
  • #1
Suekdccia
351
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TL;DR Summary
Dark Energy contribution to isothermal temperature of plasma in clusters of galaxies?
I have a question about this work called "Dark energy and key physical parameters of clusters of galaxies"*There, towards the end, the authors talk about the isothermal velocities and tempreature parameters of the gas and particles circulating between galaxies in clusters. In particular they calculate the isothermal plasma temperature (equation 37)I can note there is a contribution from a dark energy parameter in that equation (the cube root of the dark energy density value is present in the equation, which should give a large number as the dark energy density in space is small). I tried to ask the authors themselves, but they only told me that "*Temperature is defined from virial relation. It contains Dark Energy due to its antigravity*"Does it mean that dark energy contributes to the value of that temperature? Does dark energy help to increase the value of that temperature?* https://arxiv.org/abs/1206.1433
 
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  • #2
Suekdccia said:
Does it mean that dark energy contributes to the value of that temperature?
Do you understand what the authors meant by "temperature is defined from virial relation"?
 
  • #3
PeterDonis said:
Do you understand what the authors meant by "temperature is defined from virial relation"?
That the temperature is given by the virial theorem. If so, particles would reach a maximum turn-around radius and then fall into the overdensity and the potential energy would be transofrmed into kinetic energy. But how can dark energy contribute to this?
 
  • #4
Suekdccia said:
That the temperature is given by the virial theorem.
Yes. And where does the virial theorem come from? How is it derived?

Suekdccia said:
If so, particles would reach a maximum turn-around radius and then fall into the overdensity and the potential energy would be transofrmed into kinetic energy.
No such thing has to happen for the virial theorem to apply. The virial theorem relates the time averages of potential energy and kinetic energy (and the latter is in turn directly related to temperature).

Suekdccia said:
how can dark energy contribute to this?
By modifying the potential energy. Looking at how the virial theorem is derived should make this evident.
 
  • #5
PeterDonis said:
Yes. And where does the virial theorem come from? How is it derived?No such thing has to happen for the virial theorem to apply. The virial theorem relates the time averages of potential energy and kinetic energy (and the latter is in turn directly related to temperature).By modifying the potential energy. Looking at how the virial theorem is derived should make this evident.
Mmmh that is what I was thinking, if dark energy modifies the potential energy (presumably making it larger, as particles would be less bound and could reach a higher distance) then kinetic energy should be greater as well and thus temperature increases.But the authors themselves say in this paper (https://arxiv.org/abs/1109.1215, sections 3 & 4) that the potential energy (and therefore the kinetic energy) is decreased in the presence of dark energy (because when things fall into the overdensity, dark energy affects the gravitational pull, thus reducing the energy) so according to this, temperature should be lower (as kinetic energy is also reduced because there is less potential energy). This is what I don't really understand
 
  • #6
Suekdccia said:
if dark energy modifies the potential energy (presumably making it larger, as particles would be less bound and could reach a higher distance)
"Larger" in the sense of "less negative", yes. But the virial theorem says that the time average of the kinetic energy is (half of) minus the time average of the potential energy. So a larger, i.e., less negative, potential energy means a smaller kinetic energy because of the minus sign.
 
  • #7
PeterDonis said:
"Larger" in the sense of "less negative", yes. But the virial theorem says that the time average of the kinetic energy is (half of) minus the time average of the potential energy. So a larger, i.e., less negative, potential energy means a smaller kinetic energy because of the minus sign.
But then here what I understand is that dark energy ultimately reduces the kinetic energy, which should then reduce the temperature, not increase it (dark energy density seems to contribute to the temperature of the gas in the paper that I cited in my original question, so a larger dark energy density should mean that the isothermal teperature is larger as well)

If you look at eq. 37 (https://arxiv.org/abs/1206.1433) and you assume a larger value for dark energy density then the temperature increases not decreases
 
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  • #8
Suekdccia said:
what I understand is that dark energy ultimately reduces the kinetic energy, which should then reduce the temperature, not increase it
It reduces the temperature compared to a system that is otherwise the same, but without the dark energy. But that is not what is being done in the section of the paper where eq. 37 appears.

Suekdccia said:
If you look at eq. 37 (https://arxiv.org/abs/1206.1433) and you assume a larger value for dark energy density then the temperature increases not decreases
Yes, but this equation is not comparing a system with dark energy to an identical system without dark energy. So it is irrelevant to the comparison you have been asking about. To put this another way, eq. 37 is not giving the "contribution of dark energy" to the isothermal plasma temperature, which is what you have been asking about. It is just giving the overall temperature taking all contributions into account.

What eq. 37 is doing is assuming that the gravitating system is the maximum size that it can be based on the dark energy density; this size is called ##R_\Lambda## earlier in the paper. But that size decreases as the dark energy density increases; see eq. 6 in the paper. In fact, if we use eq. 6 to rewrite eq. 37 in terms of ##R_\Lambda##, we get

$$
T_{iso} = \frac{m}{3k} \frac{M}{R_\Lambda}
$$

In other words, as the dark energy density increases, the maximum possible size of the bound system gets smaller, which means it is more compact, and a more compact gravitating system will have a higher temperature.
 

FAQ: Dark Energy contribution to plasma temperature in galaxy clusters?

What is dark energy and how does it relate to galaxy clusters?

Dark energy is a mysterious form of energy that makes up about 68% of the universe and is responsible for its accelerated expansion. While dark energy primarily affects the large-scale structure of the universe, its direct impact on the plasma temperature within galaxy clusters is minimal. However, understanding dark energy helps in studying the overall dynamics and evolution of galaxy clusters.

How does dark energy influence the temperature of plasma in galaxy clusters?

Dark energy does not directly influence the temperature of plasma in galaxy clusters. The temperature of the intracluster medium (ICM) is primarily determined by gravitational interactions, mergers, and shock heating. Dark energy's role is more indirect, affecting the large-scale structure and expansion rate of the universe, which in turn can influence the formation and evolution of galaxy clusters.

Can dark energy be detected through observations of galaxy clusters?

Dark energy itself cannot be directly detected through observations of galaxy clusters. However, its effects can be inferred by studying the large-scale distribution of galaxy clusters, their growth rate, and the dynamics of the universe. Observations such as the Sunyaev-Zel'dovich effect and X-ray emissions from the ICM can provide insights into the properties of galaxy clusters, which can then be used to constrain models of dark energy.

What role does dark energy play in the evolution of galaxy clusters?

Dark energy influences the evolution of galaxy clusters by driving the accelerated expansion of the universe. This expansion affects the rate at which galaxy clusters form and grow. As the universe expands more rapidly due to dark energy, the growth of large-scale structures like galaxy clusters slows down, leading to fewer mergers and a different distribution of cluster sizes over time.

Are there any alternative theories to dark energy that could explain the observed properties of galaxy clusters?

Yes, there are alternative theories to dark energy that attempt to explain the observed accelerated expansion of the universe and the properties of galaxy clusters. These include modifications to general relativity, such as f(R) gravity and scalar-tensor theories, as well as the concept of dark fluid, which combines dark matter and dark energy into a single entity. However, dark energy remains the most widely accepted explanation due to its consistency with a wide range of cosmological observations.

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