[jsaldea12 (OP)]

Which  is colder:  vacuum outer space or core of super-galaxy?

I say, it is vacuum outer space.

Jsaldea12
3.30.19

[Bored chemist]

I say, it is vacuum outer space.

Jsaldea12
3.30.19

I say it's silly to date stamp a post to a site that automatically does that for you.

BTW, a vacuum does not have a defined temperature.

[Kryptid]

If you're talking about the black hole thing again (and I know you are), then the black hole is hotter than the vacuum of space. A black hole's temperature would be a combination of the temperature of its Hawking radiation and whatever is going into it. So even if a black hole is sitting with nothing around it except for the cosmic microwave background, then its temperature is going to be the Hawking radiation temperature plus the microwave background temperature. For most black holes, the Hawking radiation is very cold, so it would only be very slightly warmer than the microwave background alone.

[jsaldea12 (OP)]

Yes, it is correct, vacuum outer space is colder. The  coldest temperature is pegged -272 C, meaning, the measurement is pegged at that absolute zero, minus CMBR..  But  are you sure there is Hawking radiation because hawking himself reject EH? Without EH, where is hawking radiation. Jsa 3.30.19

[Bored chemist]

The  coldest temperature is pegged -272 C, meaning, the measurement is pegged at that absolute zero, minus CMBR.

The background isn't at -272C
It's about 2.73K
Which is -270.4C

The CMBR isn't absolute zero and nor is the hawking radiation.

[Kryptid]

But  are you sure there is Hawking radiation

I cannot be sure of it until it is detected, but it has a good theoretical foundation.

because hawking himself reject EH?

No he didn't. He even mentions them in the last paper he wrote before his death: https://arxiv.org/pdf/1810.01847.pdf

Consider a hypersurface Σ_div which divides the black hole spacetime into a black hole region and an asymptotically flat region with a hole. Σ_div may be taken to be the stretched horizon, the event horizon or in stringy cases the outer boundary of an AdS region: for the purposes of microstate counting the difference will be subleading and the distinction irrelevant.

[evan_au]

then its temperature is going to be the Hawking radiation temperature plus the microwave background temperature

Let’s imagine a spacecraft in close orbit around an isolated stellar-mass black hole (no accretion disk). Close enough so that the event horizon fills half the sky, and the orbital velocity is around c/3.

Some back of the envelope guesstimates:
The temperature of the Hawking radiation is nanokelvins. The temperature of CMBR is 2.7K, for observers in deep space.

But Special Relativity says CMBR temperature will be something like 50% higher for an object this far down a gravitational well. Doppler effect says that CMBR will be something like twice as hot again in the forward direction, and half in the rearward direction.

Hawking radiation will also be hotter this close to a black hole, but it’s still nanoKelvins.

Overall, the effective temperature is about the same as CMBR in deep space.

[evan_au]

Core of a super  galaxy

This is not an isolated black hole.
The sky is filled with stars, much denser than the suburbs where the Sun lives.
The black hole will be drawing in gas and dust, producing a hot plasma in the accretion disk. 

[Kryptid]

Overall, the effective temperature is about the same as CMBR in deep space.

I'm not sure how this invalidates what I said. Sure, you can argue that 1.000000001 is "about" the same as 1, but it isn't exactly the same. I know this is splitting hairs and you couldn't tell the difference from a human perspective.

[pensador]

Which  is colder:  vacuum outer space or core of super-galaxy?

I say, it is vacuum outer space.

Jsaldea12
3.30.19

I say its the Boomerang Nebulae https://www.constellation-guide.com/boomerang-nebula/ @ 1 Kelvin

The centre of a Black hole must be hot if the laws of thermodynamics hold. The accretion disc outside the black hole is plasma. The Black hole itself will not allow heat to escape like a thermos flask, perhaps a little Hawking radiation might get out.

Space is typically 2.7Kelvin due to CMBR. The boomerang nebulae wins.

Edit I have changed my mind I forgot that Absolute zero has almost been achieved in the lab in Italy https://timesofindia.indiatimes.com/home/science/Lowest-temperature-ever-in-universe-recorded-at-Italian-lab/articleshow/44907265.cms -273.144C
A black hole of one solar mass (M☉) has a temperature of only 60 nanokelvins https://en.wikipedia.org/wiki/Hawking_radiation
And technically below absolute zero was achieved in 2013 https://scitechdaily.com/quantum-gas-temperature-goes-below-absolute-zero/

[Bored chemist]

Edit I have changed my mind I forgot that Absolute zero has almost been achieved in the lab in Italy https://timesofindia.indiatimes.com/home/science/Lowest-temperature-ever-in-universe-recorded-at-Italian-lab/articleshow/44907265.cms -273.144C

That's impressive- especially for something that big, but it's a long way from the record.
http://ltl.tkk.fi/wiki/LTL/World_record_in_low_temperatures

[pensador]

Edit I have changed my mind I forgot that Absolute zero has almost been achieved in the lab in Italy https://timesofindia.indiatimes.com/home/science/Lowest-temperature-ever-in-universe-recorded-at-Italian-lab/articleshow/44907265.cms -273.144C

That's impressive- especially for something that big, but it's a long way from the record.
http://ltl.tkk.fi/wiki/LTL/World_record_in_low_temperatures

Classically you win, but quantum mechanically I found a link below absolute zero, which I am not convinced is valid.

Zero Point energy will always prevent absolute zero being reached. https://en.wikipedia.org/wiki/Zero-point_energy

But even if we start travelling through space at absolute zero, if the unruh effect is taken into account it becomes warmer.https://en.wikipedia.org/wiki/Unruh_effect

[Bored chemist]

Below absolute zero is sort of possible; but it's not really a temperature.
A laser requires a population inversion and you can call that a negative  absolute temperature but it's a stretch

[pensador]

Below absolute zero is sort of possible; but it's not really a temperature.
A laser requires a population inversion and you can call that a negative  absolute temperature but it's a stretch

The interesting thing ref temperature of a blackhole is the reference frame, accelerated away from or in free fall towards. I mentioned the UNRUH effect above, If you are in free fall towards a blackhole neglecting the accretion disk. All you would see is virtual particles, and maybe some Hawking Radiation popping into existence. If you were a stationary observer outside the event horizon, you would be undergoing acceleration due to the Black Holes Gravity, and the virtual particles that existed for a free falling observer would become real, and space would appear warm.

[jsaldea12 (OP)]

Please inform what are the temperatures of EH and hawking radiation. jsa 4.1.19

[pensador]

Please inform what are the temperatures of EH and hawking radiation. jsa 4.1.19

The temperature of Event Horizons and Hawking radiation are dependent on the size of the Black Hole, The Bigger the blackhole the lower the temperature, smaller blackholes "THEORETICALLY"evaporate much faster at increasingly higher temperatures until they reach a critical mass and explode releasing lots of energy. This has never been detected, but physicists are looking.


Here is a noddy level UTUBE on the subject

Here is a wiki link on Hawking radiation to explain it further in text https://en.wikibooks.org/wiki/General_Astronomy/Black_Holes/Hawking_Radiation A method of calculating the temperature is given in the wiki link

[jsaldea12 (OP)]

If EH and hawking radiation is cool, how come the the completely surrounding, covering  dust and gas are burning. jsa 3.5.19

[pensador]

If EH and hawking radiation is cool, how come the the completely surrounding, covering  dust and gas are burning. jsa 3.5.19

High speed collisions of other hot stuff in the EH

[jsaldea12 (OP)]

The temperature of super-jets at almost speed of light is trillion C jsal.

[Kryptid]

The temperature of super-jets at almost speed of light is trillion C jsal.

And?