> 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
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.
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.