4 ms·
Going to leave this gem here: https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator https://www.vttoth.com/CMS/physics-notes/311-hawking-ra
by brucethemoose2 3y ago
Going to leave this gem here:
https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator https://www.vttoth.com/CMS/physics-notes/311-hawking-radiati...
Black holes are weird because they are essentially macroscopic particles with only one variable, mass (ignoring angular momentum, charge and other details for the moment). But they scale very strangely.
For instance, its interesting to see what a black hole is like that emits precisely 100W of radiation. Or that is as big as a apple, or weighs as much as a apple. Or one that lives exactly 100 years, or that is as dense as water (as black holes have the odd property of getting less 'dense' as their mass grows). Its very unintuitive, and just punching values into the calculator illustrates it perfectly.
I bring this up because the illustration (a town sized black hole sitting over New York) is a very specific configuration, and it doesn't really illustrate how oddly these objects scale.
- bmitc 3y ago> as black holes have the odd property of getting less 'dense' as their mass grows What is a black hole's density?
- hazbot 3y agoMass divided by volume encased by the event horizon?
- bmitc 3y agoIsn't it thought that a black hole's mass is concentrated in the center in a miniscule volume, such that the mass is not distributed throughout the "volume" contained by the event horizon? I'm not understanding what density means for a black hole when it isn't known what's between the singularity and event horizon.
- hazbot 3y agoI think from the outside, it doesn't matter whether the mass is uniformly distributed throughout the volume or concentrated at the centre - you would feel the same force of gravity. (I'd be interested to hear if there is an experiment you could do just measuring gravity to differentiate between the two!)
- ithkuil 3y agoFor me, the most counterintuitive thing is that the more energy you put in the colder the black hole becomes. Is there any other object that behaves that way?
- bonki 3y agoLots of human beings behave exactly like that...
- nh23423fefe 3y agotemperature is analogous to surface gravity which gets weaker at the event horizon as the black hole grows. temperature is not expectation of a kinetic energy distribution of micro constituents. you don't measure a black holes temperature with a thermometer because you can't get information out of a black hole
- ithkuil 3y agoDoesn't a black hole radiate hawking radiation and a smaller black hole radiate with a higher temperature than a bigger one?
- nh23423fefe 3y agoYup wikipedia agrees, temperature is inversely proportional to mass. Surface gravity as well. https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_evaporation https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e... https://en.wikipedia.org/wiki/Surface_gravity#Schwarzschild_solution https://en.wikipedia.org/wiki/Surface_gravity#Schwarzschild_...