What is the temperature inside a black hole?

12 August 2012

Question

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

Answer

Dominic - It's actually incredibly hot. At least the surface of the black hole is very hot because as material is falling in towards the black hole, it's 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 doesn't 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 it's actually past the event horizon, it's very difficult for us to say what happens to that material beyond that point because we can't see it and we don't fully understand what laws of physics apply inside the black hole itself.

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