[froeb]

The textbook black hole is unphysical though, it assumes spacetime is asymptotically flat. As far as I can tell, the paper's claim is that if you do black holes more realistically, including better boundary conditions, then you can find solutions that have dark energy inside them, purely from GR. I wouldn't call that new physics exactly, I would call that a better understanding of physics we already have.

[T-A]

> the paper's claim is that if you do black holes more realistically, including better boundary conditions, then you can find solutions that have dark energy inside them, purely from GR

The theory paper they quote is here: https://iopscience.iop.org/article/10.3847/1538-4357/ab32da

Its main claim is that a convergent perturbation series representation of metric and Einstein tensor (assuming that one exists) requires "all pressures, everywhere, including the interiors of compact objects" to be averaged over. So if there are compact objects with dark energy interiors, they contribute negative pressure to the overall average. But the construction of a realistic GEODE (GEneric Objects of Dark Energy) "is an open question that is beyond the scope of this paper."

Generally speaking, you can't get negative pressure "purely out of GR". It's a job for the non-gravitational "stuff" on the right-hand side of Einstein's equations; either exotic configurations of known fields or new, hypothetical ones with intrinsic exotic properties. In cosmology it's typically the latter.

[raattgift]

[More realistic black holes with]

> better boundary conditions

Ok, what's the curvature scalars about one AU from the one solar mass? How about at about 50 AU (Pluto)? Or about 1000 AU (Sedna)? Or at about 0.8 light years (50 000 AU, in the Oort cloud)?

At what point do we decide that the roughly Schwarzschild metric is no longer useful at predicting the trajectories of things near that central mass? Do we care about the exact contribution of our sun to the invariants in our galaxy's central mass, or Andromeda's? Does a (were-)wolf's baying cause the moon's orbit to change such that it becomes full at a convenient time? The baying does participate in the generation of the 'true' metric, in principle.

[Black holes whose metrics aren't]

> asymptotically flat

means that the scalars drop to the point where we can use a procedure like Israel-Darmois to knit our solar system into the local neighbourhood within the Milky way. Or, if you prefer, that post-Newtonian corrections fall away in the weak field limit. And so we can hierarchically assemble bigger and bigger Schwarzschild or Lemaître-Tolman-Bondi or the like metrics and see that they useful in describing trajectories sufficiently close to the dominant non-relativistically-moving masses, and that Newton's gravitation is a very good approximation at a distance from them.

We do have several lines of evidence supporting this hierarchical approach, e.g the proper motion of galaxies within clusters <https://en.wikipedia.org/wiki/Proper_motion>.

[black holes with]

> dark energy inside them

[a] understates the proposed evolution of the non-cosmological-constant energy

[b] conflicts with strong evidence that our solar system is not expanding despite the also strong evidence of the large-scale expansion history of the universe

Roughly, under the contemplated model (thinking generously about how they approach McVittie-like model in light of their paper's §4.6's admission that there is no known solution to the Einstein Field Equations which couples interior vacuum energy, spin, adaptability into the expanding Robertson-Walker metric (like asymptotic flatness gives you), and the evolution from initial formation to growth via accretion)): when approximately a solar mass collapses into a black hole the matter less than a light year from it should expand in a way that does not match the behaviour of the Oort cloud or objects closer in.

In the same section they raise the hope that they can find such a model, and make reference to an existing paper which floated the idea of a gradient and dynamics to the expansion that could be modelled as particualrly relevant around collapsed stars (as opposed to not-yet-collapsed stars of similar mass). This is really deliberately heaping general-relativistic effects in, through, and around an already inherently general-relativistic compact object, followed by hunting for any observational support for that approach (and finding at best weak evidence). It's certainly not KISS.