What Causes the 2.7 Kelvin Temperature in the Vacuum of Space?

[Stephanus]

Dear PF Forum,
Thanks for helping me so far.
Lately, I've been reading Universe from nothing and quantum fluctuation.
Those are very interesting topics. And I'd like to know more about them.
And how the energy of the universe is zero.
But before I would study them, there are things that intrigue me.
I've been reading this.

A:
https://en.wikipedia.org/wiki/Warm–hot_intergalactic_medium
The warm–hot intergalactic medium (WHIM) refers to a sparse, warm-to-hot (105 to 107 K) plasma that cosmologists believe to exist in the spaces between galaxies and...

Actucally I know about it from this: How far can ge go - The limit of humanity https://www.youtube.com/watch?v=ZL4yYHdDSWs

B:
http://www.universetoday.com/77070/how-cold-is-space/
And if you travel out far away from everything in the Universe, you can never get lower than a minimum of just 2.7 Kelvin or -270.45 Celsius.

This is the temperature of the cosmic microwave background radiation, which permeates the entire Universe.

I thought in vacuum, the temperature is always zero. What causes this 2.7 Kelvin temperature?
Of course the CMB.
1. Can the nuclear reaction from the stars contribute to this temperature?
2. A and B seem contradict each other. And I've got warnings by some staffs regarding posting from unreliable links. And I don't think those links are unreliable. I've read those links a couple of times, but I still can't find the answer.
Why is that? Is the temperature in intergalactic space is hot, while the temperatur within a galaxy, in interstellar medium is cold?
And about this paragraph, still in the wiki link.

Within the WHIM, gas shocks are created as a result of active galactic nuclei, along with the gravitationally-driven processes of merging and accretion...

I think the SMBH is inside the galaxy. Isn't the gas shocks are created within the galaxy not in a location thousands of light years away?

Thank you very much for your help
Sincerely

 

[Drakkith]

1. Can the nuclear reaction from the stars contribute to this temperature?

Sure. The light from the stars would add a small amount to the temperature of any object in space. Or a lot, if you're very close to a star. That's why spacecraft that go near the Sun have to be designed to reflect most of the light and have special ways of getting rid of heat.

2. A and B seem contradict each other.

B just states that the minimum temperature an object can get to is 2.7 kelvin. It doesn't state that an object will get down to that temperature. Also, I'm not sure it applies to gas, which can actually get lower than 2.7 kelvin. A good example is the boomerang nebula, which sits at around 1 kelvin:

In 1995, using the 15-metre Swedish-ESO Submillimetre Telescope in Chile, astronomers revealed that it is the coldest place in the Universe found so far, besides laboratory-created temperatures. With a temperature of −272 °C, it is only 1 °C warmer than absolute zero (the lowest limit for all temperatures). Even the −270 °C background glow from the Big Bang is warmer than the nebula. Aside from the CMB cold spot, it is the only object found so far that has a temperature lower than the background radiation.

I believe it is able to get that low because the gas is expanding, which reduces its temperature. A bulk, solid object will not get down below 2.7 kelvin unless perhaps it is located within this cold gas (not sure though).

I think the SMBH is inside the galaxy. Isn't the gas shocks are created within the galaxy not in a location thousands of light years away?

If I understand the article (and several links from the article) correctly, the shocks originate when particles accelerated by the SMBH out of the galaxy and into the intergalactic medium, creating the shocks and heating the medium.

 

[Chalnoth]

I thought in vacuum, the temperature is always zero. What causes this 2.7 Kelvin temperature?

The 2.7K temperature is the temperature of the photons that make up the CMB.

The warm-hot intergalactic medium is made up of ionized atoms that are heated via a number of different processes. It stays at a higher temperature because it takes a long time for the gas to cool down, and the ionized atoms get a kick of energy from some source or another before they lose too much energy (e.g. a plasma shock front, or a quasar, or a supernova, or a gamma ray burst). The atoms are just so far away from one another that they don't really contribute to the CMB at all (which is far, far brighter).

 

[Stephanus]

Thanks @Drakkith
Thanks @Chalnoth

...The warm-hot intergalactic medium is made up of ionized atoms that are heated via a number of different processes.

What processes?

...and the ionized atoms get a kick of energy from some source or another before they lose too much energy (e.g.
- a plasma shock front, or
- a quasar, or
- a supernova, or
- a gamma ray burst). The atoms are just so far away...

These processes?
But, aren't supernova inside a galaxy, and they warm some locations far away from them?

Before they lose too much energy
So, the atoms in intergalactic medium are slow to lose energy compared to the atoms inside a galaxy/interstellar medium?

Thanks for the answers.

 

[Stephanus]

So, the hot temperatur in intergalactic space comes from quasar, neutron star, gamma ray burst, not that the space warm itself?

 

[Chalnoth]

Thanks @Drakkith
Thanks @Chalnoth
What processes?These processes?
But, aren't supernova inside a galaxy, and they warm some locations far away from them?

Right. But they send out a lot of high-energy photons, which occasionally bounce into the warm-hot intergalactic medium. It's definitely rare for these to collide, but apparently the atoms cool only very slowly, so the small number of high-energy photons are enough to keep the medium hot and ionized.

 

[Stephanus]

Thank you very much @Chalnoth
It's clear then.
I thought the intergalactic space gets hot by itself, just as Hubble Law. That intergalactic space expands by itself.
So, it does not. All the energy comes from inside the galaxies.

 

[Bandersnatch]

@Stephanus don't confuse metric expansion of the universe with expansion of hot intergalactic medium! All the properties of the matter in the universe apart from its density have no bearing on the expansion. You can't treat it as if it were an ideal gas.
So space does expand by itself in the sense that it is not powered by anything either inside, nor outside galaxies.

 

[PeterDonis]

space does expand by itself in the sense that it is not powered by anything either inside, nor outside galaxies.

This way of stating it can be misleading (as a number of other recent threads have shown). A better way to say it would be that what we call the "expansion of the universe" does not depend on any of the internal dynamics of galaxies, or intergalactic gas clouds, or any such objects. Except for the acceleration due to dark energy, the expansion of the universe is entirely a matter of inertia--the universe at the end of inflation was in a very hot, dense, rapidly expanding state, and today's expansion is just the extrapolation of that forward by 13.8 billion years or so, taking into account the average density of matter and energy.

 

[Stephanus]

@Stephanus don't confuse metric expansion of the universe with expansion of hot intergalactic medium! All the properties of the matter in the universe apart from its density have no bearing on the expansion. You can't treat it as if it were an ideal gas.
So space does expand by itself in the sense that it is not powered by anything either inside, nor outside galaxies.

Thanks @Bandersnatch for your correction.
Yes, I do know that somehow space in intergalactic medium expands, and it is not powered, as you said, by anythying inside nor outside galaxies.
What I don't didn't know was what powers the warm intergalactic medium space. But now I know. It's the supernova, quasar, gamma ray burst do that. It's not like space expansion which expands by itself and doesn't have anything to do by neither inside or outside.
Thanks
[Add:
Actually I want to know why the universe comes from nothing.
- Why the net energy in the universe is zero
- What is the total energy in the universe.
And if space in intergalactic medium can get warm by itsefl, wouldn't it be difficult to calculate the total energy of the universe?
But those belong to a new thread I think.
Now, I just want to try to calculate the total energy of the universe.
Wiki says that the universe is
4.66% matter (and energy I think)
23% dark matter
72% dark energy,
But this also belong to a new thread.
]

 

[PeterDonis]

But this also belong to a new thread.

Yes, so please start one if you want to discuss further. But before doing that, you might want to search the forums for previous threads on "the total energy of the universe", and on "the universe came from nothing". You appear to have misconceptions about these concepts that you should correct before posting about them.

 

[Stephanus]

Thanks @PeterDonis
Of course I wouldn't ask these questions
- Total energy of the universe
- Universe from nothing
in this thread.
I have misconception about this. But one thing that I want to know is whether the warm hot intergalactic medium is a special space property such as the space expansion as mentioned in Hubble Law, or it's caused by galaxies around it.
And I have had the answer in this thread. They are supernova, gamma ray burst, active galaxy nuclei.
To know further about those topics I have to read several sources further.
Thank you very much.

 

[PeterDonis]

Of course I wouldn't ask these questions
- Total energy of the universe
- Universe from nothing
in this thread.

My point is that you shouldn't ask them at all; you should first spend some time looking up references--previous PF threads, and good textbooks or papers on cosmology. Sean Carroll's lecture notes on GR contain good information along these lines. Looking up good references and understanding them should show you that neither of these questions are well posed; they don't have well-defined answers at all. So it's pointless to ask them.

 

[Stephanus]

My point is that you shouldn't ask them at all; you should first spend some time looking up references--previous PF threads, and good textbooks or papers on cosmology. Sean Carroll's lecture notes on GR contain good information along these lines. Looking up good references and understanding them should show you that neither of these questions are well posed; they don't have well-defined answers at all. So it's pointless to ask them.

Ahh, that's your point!
Not to ask them in this thread but not to ask them at all! Thanks.
I'll do my reading.
Sean Carroll? Thank you very much