I read the article, but not the paper. The article's quite popsci, I think.
No doubt I misunderstood, but it sounds like circular reasoning:
* Cosmic expansion of spacetime causes expansion of black holes
* An expanded black hole must have greater mass
* Increasing mass of black holes results in cosmic expansion of spacetime
I had also understood that cosmic expansion affects the empty space between galaxies, and doesn't affect concentrations of mass like galaxies and black holes. IOW, expansion causes galaxies to move further apart, but not stars in galaxies. If that's right (I assume it isn't), then cosmic expansion shouldn't be able to cause a black hole to expand.
Einstein’s equations, however, give no prescription for converting the actual, position-dependent, distribution of stress-energy observed at late times into a position-independent source. Croker & Weiner (2019) resolved this averaging ambiguity, showing how the Einstein–Hilbert action gives the necessary relation between the actual distribution of stress- energy and the source for the RW model.
A consequence of this result is that relativistic material, located anywhere, can become cosmologically coupled to the expansion rate. This has implications for singularity-free BH models, such as those with vacuum energy interiors. The stress-energy within BHs like these, and therefore their gravitating mass, can vary in time with the expansion rate. The effect is analogous to the cosmological photon redshift, but generalized to timelike trajectories.
So, yes two different things are presupposed through refined cosmological models:
1) singularity-free black holes limited by vacuum energy and
2) relativistic mass becoming cosmologically coupled to the expansion rate of the universe.
In that case BHs can so-to-speak be "red-shifted" by expanding (empty) space via vacuum-energy and gain mass (> stellar remnant k=3 BHs are the astrophysical origin for the late-time accelerating expansion of the universe.)
One thing to keep in mind, GR as geometrical modeling (field equations) of the universe is at its heart reciprocal. Wheeler[1] captured this succinctly in the now-famous statement: Space-time tells matter how to move; matter tells space-time how to curve.
Comments
I read the article, but not the paper. The article's quite popsci, I think.
No doubt I misunderstood, but it sounds like circular reasoning:
* Cosmic expansion of spacetime causes expansion of black holes
* An expanded black hole must have greater mass
* Increasing mass of black holes results in cosmic expansion of spacetime
I had also understood that cosmic expansion affects the empty space between galaxies, and doesn't affect concentrations of mass like galaxies and black holes. IOW, expansion causes galaxies to move further apart, but not stars in galaxies. If that's right (I assume it isn't), then cosmic expansion shouldn't be able to cause a black hole to expand.
Citing from the paper [0]
So, yes two different things are presupposed through refined cosmological models: 1) singularity-free black holes limited by vacuum energy and 2) relativistic mass becoming cosmologically coupled to the expansion rate of the universe.
In that case BHs can so-to-speak be "red-shifted" by expanding (empty) space via vacuum-energy and gain mass (> stellar remnant k=3 BHs are the astrophysical origin for the late-time accelerating expansion of the universe.)
One thing to keep in mind, GR as geometrical modeling (field equations) of the universe is at its heart reciprocal. Wheeler[1] captured this succinctly in the now-famous statement: Space-time tells matter how to move; matter tells space-time how to curve.
[0]https://iopscience.iop.org/article/10.3847/2041-8213/acb704/...
[1]https://aapt.scitation.org/doi/abs/10.1119/1.16710?journalCo...
To my limited understanding, it seems like it's a cycle just as you described, but not circular reasoning.
The reasoning is based on mathematics in previous work and observations consistent with those models reported here.