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>How would you detect one? I wonder if the gravitational wave signature of a merger between an extremal black hole with something else would give us any clues.

by floxy 2y ago

observationist 2y ago
You might see something that appears to fall into nothing, with observable massive fluctuations in gravity - anything close by would get disintegrated, observing such an event would result in a treasure trove of data, as long as it's very, very far away. The secondary damage would be something like a particle accelerator bubble on the scale of multiple solar systems.
- dotancohen 2y ago
  But it would not be falling into "nothing". There is an accretion disc.
  - ben_w 2y ago
    There can be an accretion disc, but it's not a necessary property for a black hole to have.
    - mystified5016 2y ago
      AIUI the tidal forces and spacetime distortion are such that any matter falling in inevitably breaks apart into an accretion disk. It should be impossible for a whole body to enter a black hole intact. All this is for a spinning black hole, of course, which most (all?) are.
      - floxy 2y ago
        Tidal forces at the event horizon of supermassive black holes are negligible. https://spacemath.gsfc.nasa.gov/blackh/4Page33.pdf https://spacemath.gsfc.nasa.gov/blackh/4Page33.pdf
  - observationist 2y ago
    This type of black hole is similar to dark matter, in that it warps local spacetime, but at the surface, the gravity is null, there's a weird spacetime topology to it, from what I can understand (I am not a physicist). It would be invisible, and any mass that went in would see an equivalent ejection of energy out, and the form of that energy would be fascinating. If you shot a planet into one of those at relativistic speeds it'd be a totally different, more catastrophically massive explosion than anything we've ever seen, and the volume of space around it would present opportunities to study extreme energy physics. One of the weird features is that because it cannot contain any more energy or mass, it has to immediately expel any additions, so the form of the energy coming out would be interesting to observe.

>How would you detect one? I wonder if the gravitational wave signature of a merger between an extremal black hole with something else would give us any clues.

by floxy 2y ago

>How would you detect one? I wonder if the gravitational wave signature of a merger between an extremal black hole with something else would give us any clues.

observationist 2y ago

You might see something that appears to fall into nothing, with observable massive fluctuations in gravity - anything close by would get disintegrated, observing such an event would result in a treasure trove of data, as long as it's very, very far away. The secondary damage would be something like a particle accelerator bubble on the scale of multiple solar systems.

dotancohen 2y ago
But it would not be falling into "nothing". There is an accretion disc.
- ben_w 2y ago
  There can be an accretion disc, but it's not a necessary property for a black hole to have.
  - mystified5016 2y ago
    AIUI the tidal forces and spacetime distortion are such that any matter falling in inevitably breaks apart into an accretion disk. It should be impossible for a whole body to enter a black hole intact. All this is for a spinning black hole, of course, which most (all?) are.
    - floxy 2y ago
      Tidal forces at the event horizon of supermassive black holes are negligible. https://spacemath.gsfc.nasa.gov/blackh/4Page33.pdf https://spacemath.gsfc.nasa.gov/blackh/4Page33.pdf
- observationist 2y ago
  This type of black hole is similar to dark matter, in that it warps local spacetime, but at the surface, the gravity is null, there's a weird spacetime topology to it, from what I can understand (I am not a physicist). It would be invisible, and any mass that went in would see an equivalent ejection of energy out, and the form of that energy would be fascinating. If you shot a planet into one of those at relativistic speeds it'd be a totally different, more catastrophically massive explosion than anything we've ever seen, and the volume of space around it would present opportunities to study extreme energy physics. One of the weird features is that because it cannot contain any more energy or mass, it has to immediately expel any additions, so the form of the energy coming out would be interesting to observe.