Science Questions

What is the temperature inside a black hole?

Sat, 11th Aug 2012

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David Spence asked:

Hi Chris


If a Black Hole's gravitational pull is so strong that light itself (and I presume all aspects of the Electro Magnetic Radiation) cannot escape from it, what (if any) temperature would a Black Hole be at its surface if or within? (assuming it is either equal to or just above Absolute Zero of - 273.15 Celsius, - 459.67 Fahrenheit)


Kind Regards



David Spence

Lerwick, Shetland Islands, Scotland


Dominic -   Itís actually incredibly hot.  At least the surface of the black hole is very hot because as material is falling in towards the black hole, itís being compressed into an ever smaller volume of space.  There's less space close to the black hole than there is far away from it and so, that material is elevated to tremendous pressures and tremendous temperatures of hundreds of millions of degrees, which means it doesnít glow red hot.  It glows hot in ultraviolet and x-ray light.  And that is how we can detect that black holes are there because we can set this very hot material producing x-rays with x-ray telescopes.  Once itís actually past the event horizon, itís very difficult for us to say what happens to that material beyond that point because we can't see it and we donít fully understand what laws of physics apply inside the black hole itself.


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In theory, the temperature as seen from outside a black hole is thought to be determined by Hawking Radiation.


A black hole about the mass of the Moon would have a temperature around 2.7 kelvin.

Temperature is inversely proportional to mass

When a black hole reaches zero mass, it is thought to explode in a blaze of gamma rays

Some LHC scientists hope they can produce some tiny black holes, and this temperature could then be measured to confirm the theory

The temperature inside a black hole (like most things inside a black hole) is pure speculation, and some would say, unknowable. LHC scientists aren't expecting to answer this one any time soon! evan_au, Fri, 10th Aug 2012

We cannot know by observation but simple theoretical physics can tell us sometthing

Let us assume that the black hole was quiet in that nothing much was falling into it after its first creation on a big collapse. 

The physics of black holes tells us that nothing much changes except being cut off from the rest of the universe and it would be quite possible for a spaceship o enter a very large black hole and notice nothing much happening locally.

At the time of the big collapse the material falling into the hole will be very hot so just after the collapse it will be very hot however as the collapse continues the gravity round the collapsing material will get stronger and energy will not be able to reach the first even horizon so the temperature will probably drop to around the Hawking temperature for a black hole of that size which is very cold.

If there is other hot stuff falling in this will make the local temperature hot again if course. Soul Surfer, Sat, 11th Aug 2012

Some black hole candidates reveal themselves because the accretion disk around them is so hot that it emits X-Rays as matter is shredded and falls into the black hole.

When it comes to temperature within the black hole:
Temperature is a measure of the distribution of the velocity of a particle over time.

Some theories suggest that within a black hole, our usual definitions of time & space get scrambled, and time becomes imaginary. Conventional definitions of temperature may require some revision in such an environment. evan_au, Sat, 11th Aug 2012

Heh, temperatures are interesting, as they are symmetry breakers. Wish we had some way to find out, there are some ideas with using light to simulate a Black Hole?

Don't know if one could find some equivalence to temperatures there?
Maybe? yor_on, Sun, 12th Aug 2012

I am intrigued with there being any temperature on the surface, if indeed there is one, of a blackhole, if the laws of thermodynamics is anything to go by. I understand that temperature is a measurement of the energy state of atoms in motion as well as the density (pressure) in which x number of atoms occupy in a given space. However, if one is to believe that matter cannot travel faster than the speed of light, and that light (and one would assume matter (atoms) itself cannot escape the gravitational pull of a blackhole, how could one actually measure any temperature of a blackhole unless one is measuring the energy of the matter going into a blackhole, but not the actual blackhole itself.........since matter and energy cannot escape, as mentioned previously, the gravitational pull (surface I suppose) pull????  :D unstman, Sun, 12th Aug 2012

@unstman - there are two extreme conditions under which you could observe a black hole:

A black hole which is actively absorbing a cloud of gas (or even a star), in which case friction in the accretion disk causes the gas to be raised to extremely high temperatures, in the traditional manner.

It is theoretically possible that a black hole in interstellar space could avoid swallowing any matter for some time. The traditional definition of temperature does not apply as there are no particles to measure, and we are left with a quantum-level effect called Hawking Radiation (after Stephen Hawking, who discovered the possibility). This would produce "black-body radiation" from a "black hole" which has an equivalent temperature - which is very cold for a macroscopic black hole.

Most black holes are somewhere in-between, always swallowing radiation, often swallowing atoms of gas, and occasionally, larger lumps of matter.

evan_au, Wed, 15th Aug 2012

might be that just like there are different types of planets, stars, asteroids, comets, solar systems, galaxies, etc.

makes sense that there could be different "types" of black holes that could have different properties.

I love black holes, my favorite enigma.

solving that mystery is gonna revolutionize science... Emc2, Thu, 16th Aug 2012

"makes sense that there could be different "types" of black holes that could have different properties."  At the moment the theory says that blackholes can be completely described by just three parameters: mass, angular momentum, and charge.  This may change but it will require a substantial reworking of the ideas.  imatfaal, Fri, 17th Aug 2012

  interesting Emc2, Sat, 18th Aug 2012

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