4 ms·

Do all black holes with the same mass and other 'hairless' parameters (momentum, etc) have the same temp and therefore radiation emissions? If so, can we remote

Do all black holes with the same mass and other 'hairless' parameters (momentum, etc) have the same temp and therefore radiation emissions? If so, can we remotely measure mass from this?

PaulHoule 5y ago
Except in the real world for any black hole we observe (stellar mass or larger) that temperature is much lower than the cosmic microwave background so that you won’t see it. A stellar black hole floating out between the galaxies would not be evaporating now but rather slowly gaining energy from the CMB. The universal will have to expand for a long time before it gets cooler than black holes.
- jvanderbot 5y ago
  But, my main question: Do they all have the same temp, given all other main parameters?
  - WJW 5y ago
    That depends on if they have hair or not, but nobody knows whether they do and it would be extremely impractical to experimentally verify such a thing. That's what the article is all about. If they don't have hair then yes, you should be able to estimate mass by measuring their temperature. You would also need to know how far it is though, so that you could compensate for redshift.
    - jvanderbot 5y ago
      OK, that makes sense. In reading TFA I was just kind of blown away that temp, mass, angular momentum, etc, are all so closely tied together.
      - tsimionescu 5y ago
        Note that they are so closely tied together for black holes, not necessarily for other types of objects. Black holes in the GR description are probably simpler than some elementary particles even. However, it's important to note that the GR description is itself not exactly self-consistent, as the curvature is divergent at the center of the black hole (it is infinite, I believe?).
Ma8ee 5y ago
No, small black holes are hotter than big black holes.
- tsimionescu 5y ago
  Black holes of the same mass (and angular momentum and charge) have the same size.
  - Ma8ee 5y ago
    Of course. I apparently read the question to fast.

Do all black holes with the same mass and other 'hairless' parameters (momentum, etc) have the same temp and therefore radiation emissions? If so, can we remotely measure mass from this?

PaulHoule 5y ago

Except in the real world for any black hole we observe (stellar mass or larger) that temperature is much lower than the cosmic microwave background so that you won’t see it. A stellar black hole floating out between the galaxies would not be evaporating now but rather slowly gaining energy from the CMB. The universal will have to expand for a long time before it gets cooler than black holes.

jvanderbot 5y ago
But, my main question: Do they all have the same temp, given all other main parameters?
- WJW 5y ago
  That depends on if they have hair or not, but nobody knows whether they do and it would be extremely impractical to experimentally verify such a thing. That's what the article is all about. If they don't have hair then yes, you should be able to estimate mass by measuring their temperature. You would also need to know how far it is though, so that you could compensate for redshift.
  - jvanderbot 5y ago
    OK, that makes sense. In reading TFA I was just kind of blown away that temp, mass, angular momentum, etc, are all so closely tied together.
    - tsimionescu 5y ago
      Note that they are so closely tied together for black holes, not necessarily for other types of objects. Black holes in the GR description are probably simpler than some elementary particles even. However, it's important to note that the GR description is itself not exactly self-consistent, as the curvature is divergent at the center of the black hole (it is infinite, I believe?).

Ma8ee 5y ago

No, small black holes are hotter than big black holes.

tsimionescu 5y ago
Black holes of the same mass (and angular momentum and charge) have the same size.
- Ma8ee 5y ago
  Of course. I apparently read the question to fast.