Talk:Accretion disk

Please add some short info on and/or images from the study to the article. It's currently featured in 2020 in science (September) like so:

Scientists publish new findings and data about the supermassive black hole M87*, including a video of the black hole based on data not sufficient for images, using statistical modeling about changes in its appearance in 2009–2017, showing variations of its orientation and a wobbling ring – constituting the "first glimpse of the dynamical structure of the accretion flow so close to the black hole's event horizon".^[1][2]

The study and its images are licensed under CC BY 4.0 so you could upload the images or animations to Commons and add them here as adequate.

--Prototyperspective (talk) 15:54, 22 October 2020 (UTC)

This article covers Polish donuts, super-Eddington fat disks, but the situation with super-Eddington thin disks is missed, as described here: -- 65.92.246.77 (talk) 13:51, 17 November 2024 (UTC)

Protoplanetary disk article says black holes have accretion discs but stars have protoplanetary disks. This accretion disc article talks about the accretion discs of stars, but they aren’t accretion discs. 149.154.44.25 (talk) 03:43, 6 September 2025 (UTC)

I agree with @149.154.44.25: protoplanetary discs aren't accretion discs, they are just... discs. (The PP disk page explicitly says they are different and I think thats correct). This article doesn't separate these two cleanly IMO: it's using the general theory of astrophysical discs (any type) and applying it to accretion discs, but currently there isn't any explanation as to the underlying equations for discs (or their context). So it almost comes across like accretion disks are the only form of disks? Even the intro statement is IMO incorrect:

"An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body."

That is just the definition of a disk, not of an accretion disk (an accretion disk must accrete. This sentence also covers, say, Saturn's rings, which don't accrete at any meaningful rate). I would say something like: accretion discs are an astrophysical phenomenon, which can be described by the applied math/theoretical physics model of astrophysical discs.

I think this overlap is harmful to the article, as readers will assume that e.g. the alpha model section is about accretion discs only when that isn't true: it is just a mathematical model for disks, and its perfectly valid to be used in non-accretion disks. Same as the discussion on instabilities: convection, oscillations, epicycles can all occur in non-accretion disks.

There is plenty of content on accretion disc theory & their history. Same for general discs. I think theres enough for both to have their own articles.

I propose the following:

• Create a new article, titled "Astrophysical Disks". This can be a general overview of disc theory (mathematical & physical), an overview of its history, and examples of discs: accretion, protoplanetary, etc. Things such as the shearing sheet model, alpha viscocity description, Kida vortices, tidal potential, coriolis forces, shear, mass fluxes, ALMA & disc observations, discs in the solar system, stability, lifespan, etc can be included. I.e. - there's a lot (!) of information to be covered on discs that isn't currently on wikipedia

I also have some points about some of the physics on this page (Accretion Discs):

• "can be estimated as ${\displaystyle \nu =\alpha c_{\rm {s}}H}$ where..."
  • AFAIK this isn't exactly true, it is more that in the early days of discs physics you couldn't do massive N body simulations, so scientists had to come up with some way of dealing with viscosity analytically. This formula works dimensionally (nu has dimensions length^2 per time) so they ansatzed this in - because thats a reasonable first approach for analytically solving the disc equations. Okay after writing this, I'm being pedantic, it is an estimation - but not in the sense of a standard physics approximation where you Taylor expand something, or derive it from some equation after neglecting some terms. This is different - its "Hey, this works dimensionally, lets chuck it in and see what we get" rather than "I understand that under these assumptions this approximation will be valid". Its bundling up some very difficult to approximate physics into 1 term and hoping its valid. IMO this should be made clear in the article
• Also I think the maths needs a lot more context. e.g. What is the scale height of the disc? What does it represent and where did it come from? Same for the Rayleigh stability criterion (I know it has its own article, but the derivation there isn't very clear for the average reader)
• IMO the unsolved infobox is written in the wrong voice: the jets are not under the control of the astronomers, they just... exist. (I'm being facetious, but I still think the wording isn't as precise as it could be). I think it would be better worded as follows:

... These jets are used by astronomers to explain phenomena such as removal of angular momentum from a protostar, and reionizing the universe (in active galactic nuclei), but their origin is still not well understood.

This places the action on the astronomers doing the explaining, rather than the AGNs doing something that the astronomers want them to do.

• "The study of oscillation modes in accretion disks is referred to as diskoseismology". I disagree, it is the study of oscillation modes in disks (protoplanetary, planetary rings, etc. They all can have oscillations).

I think some of these points would be well addressed by creating the aforementioned "Astrophysical Disk" article, which can include the relevant fluid dynamics equations, and the origin and history of the relevant mathematics.

Conclusion

A lot of the content of this article feels like it has got disks and accretion disks confused. There are other types of disks than accretion disks, and the mathematical study of disks is not only focused on accretion. The problems with this confusion and a proposed solution(s) are given above. If there are no objections in the next 7 days (-71 days left) then I'll carry out the changes listed here and create an AfC for "Astrophysical Disk" BennBluee (talk) 04:40, 15 June 2026 (UTC)

The Disk jet unsolved infobox is also not replicated on https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_astronomy. Should probably be added BennBluee (talk) 12:12, 15 June 2026 (UTC)

The key issue is whether "Astrophysical disk" passes the general notability guidelines on its own, by exactly that name. Search on Google Scholar says no. Other evidence:

• Armitage, P. J. (2011). Dynamics of protoplanetary disks. Annual Review of Astronomy and Astrophysics, 49(1), 195-236. A generic model for the evolution of protoplanetary disks, based on the theory of geometrically thin accretion disks (Lynden-Bell & Pringle 1974),...
• Pringle, J. E. (1981). Accretion discs in astrophysics. In: Annual review of astronomy and astrophysics. Volume 19.(A82-11551 02-90) Palo Alto, CA, Annual Reviews, Inc., 1981, p. 137-162., 19, 137-162. Discusses the shift in the 1960s as black holes were first discovered.
• Bitsch, B., Johansen, A., Lambrechts, M., & Morbidelli, A. (2015). The structure of protoplanetary discs around evolving young stars. Astronomy & Astrophysics, 575, A28. The formation of planets with gaseous envelopes takes place in protoplanetary accretion discs on time scales of several million years.

While I am sympathetic to your concern, I think we should try to solve this by altering the structure of the article. Johnjbarton (talk) 16:36, 15 June 2026 (UTC)

Searching for the UK spelling astrophysical disc on google scholar does return sources with that name. e.g. there is a book on astrophysical discs.

My main point is that 'astrophysical disk' acts as the parent concept to many articles on Wikipedia (protoplanetary disk, accretion disk, ring system, galaxy disk), and we currently lack an umbrella article that explains the shared physics uniting them. I think the book is evidence that the broadest concept available in the literature is the astrophysical disk, and the current articles on Wikipedia are essentially sub-topics of this. Therefore, I believe it is justified to create a new broad-concept article for these to fit into.

In my opinion the reason "astrophysical disk/disc" doesn't return more results is because of context: when authors say "disc/disk" in the literature they are meaning "astrophysical disc". From your quote on "protoplanetary accretion discs" its clear that these articles overlap and a broad umbrella article would help disambiguate this. The 1981 Pringle reference explicitly has a section on "steady discs" (section 3) - this clearly means "steady astrophysical discs". From reading that reference, it actually starts with a general theory & overview of astrophysical discs, and then focuses on accretion. IMO this shows that the literature views astrophysical discs as an umbrella term under which accretion discs are found.

Searching for "astronomy "disc"" leads to many results. So perhaps my proposed article name is incorrect? Should it just be disk (astronomy) or something similar? My proposal was more that we need an umbrella article on discs, not that the specific name should be Astrophysical disk (I realise now that wasn't clear, apologies). I'll switch to just using "disks" now. My goal is more to create a WP:BCA that acts as an umbrella for the articles on this topic.

A generic model for the evolution of protoplanetary disks, based on the theory of geometrically thin accretion disks (Lynden-Bell & Pringle 1974),...

I do not think this provides evidence that disks are not notable. In my opinion it is actually the opposite: it shows that many different types of disk exist and share similar physics. This is exactly what my article proposal would make clear.

I do however see from your evidence that protoplanetary discs are commonly seen as accretion discs, so I was wrong on that taxonomy. BennBluee (talk) 17:50, 15 June 2026 (UTC)

I realise now my proposal should've just been for disc: I had gone one step too far and was already trying to disambiguate the article title. So I will just make my proposal clear:

I propose an article be created that covers the overall physics of Disks (astronomy), under which the many wikipedia articles on different variants of disks can be categorised. From the literature it is clear that these articles come under the broad category of disk. Many papers are published on accretion disks but that does not make the parent category any less notable. BennBluee (talk) 17:55, 15 June 2026 (UTC)

My point is that there is a fundamental missing link in the categorisation: "disk" is a parent category to "___ disk" and there is a lot of foundational math, history, observation that is not present on any of these subpages. BennBluee (talk) 18:13, 15 June 2026 (UTC)

And my point is that we summarize sources. If there is a parent category for accretion disk then there should be sources that describe it as such. We should not have to invent it.

A source that directly addresses the broad issue is

• Latter HN, Ogilvie GI, Rein H. Planetary Rings and Other Astrophysical Disks. In: Tiscareno MS, Murray CD, eds. Planetary Ring Systems: Properties, Structure, and Evolution. Cambridge Planetary Science. Cambridge University Press; 2018:549-576. https://doi.org/10.1017/9781316286791.020

This source does not support a claim that an "accretion disk" is a type of "astronomical disk". Rather it considers "accretion" to be a process that occurs within most astronomical disks. That is why many sources (and perhaps this page as well) are ambiguous. "Accretion disk" seems to be a phase disks go through. Johnjbarton (talk) 19:57, 15 June 2026 (UTC)

I appreciate the source you provided, but I believe it actually perfectly illustrates the point I am making about the need for a broad-concept article (WP:BCA).

The fact that "accretion" is a process or a phase does not change the morphological reality of the object itself: it is still, fundamentally, an astrophysical disc. Arguing that an accretion disc is not a type of disc because "accretion" is a process is a fundamental category error. It is equivalent to arguing that a "spinning top" isn't a "top" because "spinning" is a dynamic state. When the accretion phase ceases, the underlying physical structure - the disc - does not cease to be a concept governed by orbital mechanics and fluid dynamics.

To address your points directly:

1. The Evidence from Your Source

• The 2018 Latter et al. chapter you cited is literally titled: "Planetary Rings and Other Astrophysical Disks." The authors explicitly group planetary rings and other discs under the parent umbrella of "Astrophysical Disks." This directly supports the exact taxonomy and article structure I am proposing. The literature already recognizes the broad category.

2. Shared Foundational Physics

• Whethera disc is currently accreting, forming planets (protoplanetary), or acting as a debris ring, they all share identical foundational physics that do not belong siloed in the "Accretion disk" article. The fundamental mathematics of Keplerian shear, the thin-disc approximation, vertical hydrostatic equilibrium, and the Navier-Stokes equations for angular momentum transport apply to astrophysical discs broadly. Currently, Wikipedia readers have nowhere to go to understand the baseline physics of a generic disc without going through accretion-specific phenomena.

3. Alignment with WP:BCA

• Wikipedia policy on Broad-Concept Articles (WP:BCA) explicitly states that when several specific concepts (accretion discs, protoplanetary discs, debris discs, galactic discs) share a common fundamental characteristic, a broad-concept parent article should be created to cover the shared context, history, and underlying science.

I am suggesting we document the widely accepted morphological parent category that these articles share. BennBluee (talk) 20:51, 15 June 2026 (UTC)

Well I looked for and posted the source because it supports your claim of a broad category. However, your opening claim was "protoplanetary discs aren't accretion discs" which I still disagree with. Johnjbarton (talk) 21:02, 15 June 2026 (UTC)

I also now disagree with that statement (I will strike it out now) BennBluee (talk) 21:06, 15 June 2026 (UTC)