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Black Holes and Thermal Radiation

Varun G asked

“Do black holes produce thermal radiation, as expected on theoretical grounds and do they absorb light?”

Ans: Hope you are talking about the Hawking radiation.

Any body at a temperature above absolute zero emits radiations. If the temperature of black body is not absolute zero (It was Stephen Hawking who predicted that black holes should have a finite, non-zero temperature, and hence the name “Hawking Radiation”) it will emit radiation.

In a black hole emitting radiation, there is a loss of mass. If the mass decreased due to Hawking Radiation is more than the mass gained by the black holes via alternate means, the net mass of the black holes will go on decreasing. (This is called “black hole evaporation” Further, it has been noted that the black holes with lower mass emit more radiations than the heavier ones.

This answer may seem contradicting the definition of black hole itself.

“A black hole is a body whose gravitational force of attraction is so huge that even electromagnetic radiation cannot escape from it” as the definition goes.

But the Hawking Radiation is caused by Quantum effects. The processes behind the “escape” of radiation from a black hole is thought to be

  • Vacuum Fluctuations and
  • Quantum tunneling

The above terms and concept will be too high to be discussed at school level. However for the curious ones, I am giving some links to explore.


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