Can Black Holes really create Dark Energy?
A couple of papers were published recently that attracted quite a lot of media interest so I thought I’d mention the work here.
The researchers detail the theory in two papers, published in The Astrophysical Journal and The Astrophysical Journal Letters, with both laying out different aspects of the cosmological connection and providing the first “astrophysical explanation of dark energy”. The lead author of both papers is Duncan Farrah of the University of Hawaii. Both are available on the arXiv, where all papers worth reading in astrophysics can be found.
The first paper, available on the arXiv here, entitled Preferential Growth Channel for Supermassive Black Holes in Elliptical Galaxies at z<2, and makes the argument that observations imply that supermassive black holes grow preferentially in elliptical galaxies:
The assembly of stellar and supermassive black hole (SMBH) mass in elliptical galaxies since z∼1 can help to diagnose the origins of locally-observed correlations between SMBH mass and stellar mass. We therefore construct three samples of elliptical galaxies, one at z∼0 and two at 0.7≲z≲2.5, and quantify their relative positions in the MBH−M∗ plane. Using a Bayesian analysis framework, we find evidence for translational offsets in both stellar mass and SMBH mass between the local sample and both higher redshift samples. The offsets in stellar mass are small, and consistent with measurement bias, but the offsets in SMBH mass are much larger, reaching a factor of seven between z∼1 and z∼0. The magnitude of the SMBH offset may also depend on redshift, reaching a factor of ∼20 at z∼2. The result is robust against variation in the high and low redshift samples and changes in the analysis approach. The magnitude and redshift evolution of the offset are challenging to explain in terms of selection and measurement biases. We conclude that either there is a physical mechanism that preferentially grows SMBHs in elliptical galaxies at z≲2, or that selection and measurement biases are both underestimated, and depend on redshift.
arXiv: 2212.06854
Note the important caveats at the end. I gather from people who work on this topic that it’s a rather controversial claim.
The second paper, entitled Observational evidence for cosmological coupling of black holes and its implications for an astrophysical source of dark energy and available on the arXiv here, discusses a mechanism by which it is claimed that the formation of black holes actually creates dark energy:
Observations have found black holes spanning ten orders of magnitude in mass across most of cosmic history. The Kerr black hole solution is however provisional as its behavior at infinity is incompatible with an expanding universe. Black hole models with realistic behavior at infinity predict that the gravitating mass of a black hole can increase with the expansion of the universe independently of accretion or mergers, in a manner that depends on the black hole’s interior solution. We test this prediction by considering the growth of supermassive black holes in elliptical galaxies over 0<z≲2.5. We find evidence for cosmologically coupled mass growth among these black holes, with zero cosmological coupling excluded at 99.98% confidence. The redshift dependence of the mass growth implies that, at z≲7, black holes contribute an effectively constant cosmological energy density to Friedmann’s equations. The continuity equation then requires that black holes contribute cosmologically as vacuum energy. We further show that black hole production from the cosmic star formation history gives the value of ΩΛ measured by Planck while being consistent with constraints from massive compact halo objects. We thus propose that stellar remnant black holes are the astrophysical origin of dark energy, explaining the onset of accelerating expansion at z∼0.7.
arXiv:2302.07878
The first I saw of these papers was in a shockingly poor write-up in the Guardian which is so garbled that I dismissed the story out of hand. I recently saw it taken up in Physics World though so maybe there is something in it. Having scanned it quickly it doesn’t look trivially wrong as I had feared it would be.
I haven’t had much time to read papers over the last few weeks but I’ve decided to present the second paper – the more theoretical one – next time I do our cosmology journal club at Maynooth, which means I’ll have to read it! I’ll add my summary after I’ve done the Journal club on Monday afternoon.
In the meantime I was wondering what the general reaction in the cosmological community is to these papers, especially the second one. If anyone has strong views please feel free to put them in the comments box!
UPDATE: There is a counter-argument on the arXiv today.
In the Dark 
February 25, 2023 at 12:26 pm
I haven’t got any strong opinions on the cosmology take in the second paper – although might not be all that enamoured by the use of ‘black holes’ to refer to objects without a singularity.
Be that as it may, my personal biggest concern about this is not about supermassive black holes, but rather stellar mass black holes – we know of a few Msun black holes in very old globular clusters and we have very strong constraints on the existence of intermediate mass black holes in these. With the proposed scaling of M_BH \propto a^3, you have trouble both with the black holes we observe to have ~few Msun today having formed with ridiculously small masses, and also with the fact that any stellar mass BH formed from stellar evolution at high-z would have intermediate-mass today and that would be obvious in the dynamics of globulars.
Even if the ancient BHs were ejected (somehow) from the globular clusters, I suspect there would be trouble with the microlensing and stellar dynamics results that place stringent constraints on massive halo objects around the Milky Way but I haven’t actually done the numbers so might be wrong.
February 25, 2023 at 12:45 pm
Well, the Penrose BH singularity theorems apply only when the strong energy condition holds, and dark energy violates that condition so there need not be a singularity inside an object made of such stuff even if there is a horizon around it.
February 25, 2023 at 1:28 pm
That is a fair point. I guess I have just associated “Black hole” = singularity in my mind so would have preferred a different term 😀
February 25, 2023 at 1:12 pm
Next Theoritical physical prediction will be the connection between black holes and the origin of universe (Big bang and cosmic inflation included)
February 25, 2023 at 5:06 pm
Papers about universe inside black holes have been written since a long time ago (as early as 1972) https://ui.adsabs.harvard.edu/abs/1972Natur.240..298P/abstract
February 25, 2023 at 5:38 pm
The key to the present argument is about the exterior metric in a Kerr black hole.
February 25, 2023 at 5:42 pm
Thanks! I will have a look at the papers.
February 26, 2023 at 12:22 pm
Peter: I agree that the 1972 paper by Pathria is not related to this current paper. Was only answering Rodolphe’s questions that the papers he mentioned have already been written . See also https://arxiv.org/abs/1410.3881
February 26, 2023 at 4:42 am
What is the mechanism of black hole actually contributing dark energy to the universe that is outside of the black hole? As I understand no energy or matter can exit the black hole.
February 26, 2023 at 10:04 pm
Sounds interesting and would love to throw my two cents in, but I suffer from Dyscalculia….seriously.
Can you translate these findings into a consumable, more practical finished product for mathematically-challenged readers like myself, sort of like “Quantum Physics, Dark Energy and the likes for Dummies”?
Kind Regards,
Mark
February 28, 2023 at 6:23 pm
There was another argument against the BH-DE link at https://arxiv.org/abs/2302.13333 which includes the startling acknowledgement “I am grateful to Ruth Durer both for the invitation to visit Universite de Geneve and work in a calm environment without air raids and blackouts, and for drawing my attention to the article (Farrah et al, 2023a).” – and of course it turns out that the author’s affiliation is Kyiv.
March 1, 2023 at 6:17 am
I would say the papers present an interesting hypothesis, with enough evidence to make them worthy of consideration, but no more than that just yet. I’m obviously completely unbiased and objective in this view.
A few responses:
Personally I like to use ‘black hole’ to mean the astrophysical object, whatever that is, and not a solution with a singularity, but that’s just me 🙂
BHs in GCs are probably the most serious issue raised so far. Tiny BHs in old GCs could form via e.g. something related to blue stragglers, or maybe NS-NS collisions, or field capture, but its not clear if this is feasible. More speculatively, its not clear that vacuum energy remnants would have to obey the TOV limit. Ther are a few other subtleties to consider, e.g. orbital dynamics would be affected by adiabatic inspiral, but this is definitely an area the idea would have to address to be accepted.
Microlensing and other MACHO constraints are discussed in the second paper, and are (mostly) easily satisfied.
I have the utmost respect for any academic from Ukraine who can do science under those circumstances, but I fear he has missed the crux of the theoretical argument. He’s arguing against a poition that the theory does not take in the first place. For the complete argument, I suggest starting with this:
https://ui.adsabs.harvard.edu/abs/2022PhRvD.105h4042C/abstract
Then this:
https://ui.adsabs.harvard.edu/abs/2019ApJ…882…19C/abstract
note the argument against Birkhoff’s theorem, and the justification of the assumptions in S2 in Appendix B. And then for a little light reading, this:
https://ui.adsabs.harvard.edu/abs/2007PhRvD..76f3510F/abstract
March 1, 2023 at 5:20 pm
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May 21, 2023 at 8:29 am
Yes, black holes produce dark energy, dark energy produce stars, stars again end up in black holes and so cycle goes on.its energy cycle like a water cycle.everything in this world is cyclic nothing nonrepititive
July 22, 2023 at 1:17 pm
[…] papers to which this is a response are mentioned here. For reference ,these earlier works were published in The Astrophysical Journal and The […]