Could visible hawking radiation be used to illuminate an enclosed space in a way that would be useful to a human? The specific space would be habitable for the human, and be close enough to the black hole for the light to be radiated directly inside the habitat. Gravity can be ignored

  • $\begingroup$ You might be able to illuminate your habitat with the light of the accretion disk. $\endgroup$
    – Willk
    Oct 5, 2021 at 13:48

1 Answer 1


Can visible Hawking radiation be used to illuminate an enclosed space?


Will it be useful for a human?

Most likely not

According to this calculator, a black hole with Hawking radiation peaked at 500 nm has

  • a mass of $1.6 \cdot 10^{19}$ kg,
  • a Schwarzschild radius of 28 nm
  • a lifetime of $6.8 \cdot 10^{33}$ years,

but with a luminosity of just $1.5 \cdot 10^{-6}$ W.

That not enough to shine any useful light, even holding it very close to the object you want to illuminate.

  • $\begingroup$ To put that tiny radiative power in perspective, 1.5 microwatts, even if all the power goes into green light, is about 1/18,000 of the luminous intensity of a candle. That is, you would need 18,000 such black holes to put out same amount of light as one candle. $\endgroup$
    – AlexP
    Oct 5, 2021 at 11:53
  • $\begingroup$ Good God, @AlexP, not enough trouble trying to hold such an object, you want to bring 4 times the mass of Moon, in a single room, on the surface of the Earth? If you manage the feat, can you imagine how that messes with the Earth mass center and what it will do to the tides? $\endgroup$ Oct 5, 2021 at 12:02
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    $\begingroup$ You would want a frequency downstepping process. at 6e13kg you have a nice 100 kw light source, you just need to reduce the frequency from the somewhat scary 1.7e20hz very hard x-ray/ soft gamma down to visible light. A 5cm radius tungsten shell will do nicely, it will shine at a comfortable yellow-white heat(2800K), while filtering out 99.997% of the x-rays.(surface gravity is an awkward 160K g's, but....) $\endgroup$
    – PcMan
    Oct 5, 2021 at 13:02
  • $\begingroup$ Four times the mass of the moon?! At this time of year, at this time of day, at this part of the country, localized entirely inside your reading room? $\endgroup$
    – jdunlop
    Oct 5, 2021 at 17:30
  • $\begingroup$ @jdunlop time and tide wait for no man. and in this case, the grabbity from that reading lamp will really be a reallyn attractive feature. (yes grabbity. Mere Gravity can be handled, but grabbity is the strong stuff). Not to mention just how robust your lamp-post will need to be, I don't think the stuff from IKEA is rated for loads of that magnitude. $\endgroup$
    – PcMan
    Oct 6, 2021 at 8:24

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