Gravitational difference between a black hole and a star

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Discussion Overview

The discussion revolves around the differences in gravitational behavior between black holes and material objects such as stars and planets. Participants explore the implications of the 'immaterial' nature of black holes, the dynamics of various binary systems, and the effects of tidal forces and friction in these contexts.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that the material versus 'immaterial' nature of objects may influence how they curve or travel through spacetime, particularly in gravitational interactions.
  • Others argue that gravity is solely dependent on mass and rotation, suggesting that characteristics like chemistry or electrical conductivity do not affect gravitational forces.
  • There is a discussion about whether the lack of friction in black holes affects their motion through spacetime compared to material objects.
  • Some participants assert that a planet orbiting a black hole would experience tidal and gravitational forces similar to those around the Sun, while others contest this, noting differences in how a black hole and a star would deform surrounding matter.
  • Participants debate whether the tidal forces experienced by Earth would differ if the Sun were replaced by a black hole of equal mass, with some suggesting that distant orbits would not notice a significant difference.
  • There are discussions about the effects of the Moon's gravity on Earth's rotation and the implications of tidal locking, with differing views on the relevance of these effects in the context of black holes.
  • Some participants highlight the reciprocal nature of gravitational effects, questioning how a singularity's distance might influence gravitational interactions differently than a star.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the gravitational dynamics of black holes versus stars, and the discussion remains unresolved on several key points, particularly concerning the effects of tidal forces and the implications of black holes being 'immaterial' objects.

Contextual Notes

Limitations include assumptions about the nature of friction in a vacuum, the definitions of material versus immaterial objects, and the complexities of tidal interactions that are not fully explored.

  • #31
Generally, stars are sufficiently extended that, even when touching, their centers are not close enough, so their orbits are not fast enough, for these waves to carry any significant energy away: When/if they merge, it is because of classical physics, especially friction.

The exception is neutron stars. But even there, a very close pair can take 100 MYr or more for the gravitational waves to carry away enough orbital energy for a merger.
 

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