|WikiProject Physics / Relativity||(Rated B-class, Mid-importance)|
- 1 Magnitude
- 2 The theory of black holes
- 3 Conflicting info with Quasar page
- 4 Why disks?
- 5 Confusing jump
- 6 Hannes Alfven
- 7 Link Removed
- 8 Contradiction
- 9 Introduction
- 10 The Binary Star System Image
- 11 Accretionary Disc and radiation jets suggesting polarity?
- 12 Gravitational gradient of super massive black hole
Accretion discs seem to exist at the planetary scale (eg formation of Saturn and its moons) and stellar level and also at the galactic level - but not at intermediate levels. There are, for example, no globular clusters in the form of accretion discs or any Intermediate-mass black holes with proportionate accretion discs. Should the article explain this - or highlight the matter? --Tediouspedant (talk) 13:19, 7 February 2010 (UTC)
The theory of black holes
I recall reading a short article about a year ago announcing that Stephen Hawking had retracted his assertions of belief in the theory of black holes. He had done some work to reexamine the correctness of his math, and came to the realization that it wasn't necessarily true that the phenomenon we call a black hole constituted a space-time singularity. I'll try to dig up the article... Infinite.ki 00:05, 26 January 2006 (UTC)
You are mistaken. His recent work was involved with the problem of unitarity with the formation / destruction of black holes, not whether black holes as a class of objects exist or not. (Although his proof involves the fact that an observer far enough away cannot know for certain if a given black hole exists at a given location.) Anyway, accretion disks can form around neutron stars, white dwarfs, in T-tauri stars and even in the formation of a planet - so whether or not black holes exist isn't really important for this particular article. Sfuerst
I think the spelling should be changed to 'disk', though, in all references. In my experience as a trained astronomer, and as a native american english speaker, the only time the spelling 'disc' is preferred is for 'compact disc'. I cannot recall seeing 'accretion disk', 'galactic disk', 'protoplanetary disk', etc spelled any other way, in american publications. Probably happens, but certainly in the minority. Any agreement to change the name? Myrrhlin
"Accretion disk" is much more common than "Accretion disc" in the scientific literature, even though technically the word "disc" is more correct. Changing it to the more common form would probably be a good idea. Sfuerst 20:22, 18 March 2006 (UTC)
- I would be against changing to disk. Normally in the UK we use disc for accretion discs and it provides a useful distinction when writing because we tend to use disk for computer disks. This is in fact the the convention in Monthly Notices of the Royal Astronomical Society. Owen 13:32, 7 March 2007 (UTC)
The reason I changed 'protoplanetary disk' to 'nova' is that there is an accretion process going on in a protoplanetary disk which has nothing to do with accretion disks. While there _may_ continue to be accretion of H/He gas onto the protostar, this is (I would argue) not the 'accretion' one would usually be talking about in the protoplanetary disk. Use of the term 'accretion disk' to describe a protoplanetary disk leads to confusion. Please see my comments on the solar nebula.
- Actually, this isn't true, you can still treat the protoplanetary disk with an alpha-disk model. There has been recent research into the formation of gas-giant cores in disks where the MRI causes \alpha to act like a step-function with radius. (They are trying to explain why some planets migrate into the star, and others don't.) However, you are right once ogliarchic mergers start to happen - but then the disk is pretty much gone anyway. Sfuerst 19:59, 22 March 2006 (UTC)
- I have heard of these models, but my impression was they are still quite new, and dont have a lot of support among the researchers. Also, are they not specifically for gas giants? Accretion of dust particles in the traditional model is still required for terrestrial planets, isn't it? In any case, I still maintain that use of the term 'accretion disk' leads to confusion in the discussion of accretion in protoplanetary disks, because when I teach this (and I do), I am talking about accretion of solidified particles out of the gas, not accretion of gas onto the protostar or onto a jovian protoplanet (which probably has its own accretion disk). I am not arguing against alternative models. I am arguing for article clarity. It's okay to keep the term in this context, but some explanation to avoid this easy confusion makes the article better. Myrrhlin 14:01, 24 March 2006 (UTC)
Also, you reverted away the other edits I made, which may have needed some polishing, but added more information about accretion disks in close binaries with stellar remnants. I also had a sentence specifically addressing the possible confusion over the term accretion when referring to protoplanetary disks. Any comment why you removed these changes by reversion, instead of incorporating them? You marked your edit as minor. perhaps you did not notice those other changes? Myrrhlin 04:40, 21 March 2006 (UTC)
- The main problem with the second paragraph is the confusion introduced about the "size" of the companion - it was difficult to determine whether the paragraph was using mass or radius. (Astronomically, the object that is accreting is typically refered to as the 'primary' if it has more mass, yet you were calling it the "lesser companion".) Note that the more massive companion is often physically smaller in radius than the less massive companion... however this is not always the case. For example NS-NS binaries are thought to form in a process where both stars accrete mass from the other as they each go through the red-giant stage in turn. Since the more massive star reaches the red giant branch first, it will then give mass to the less massive star which is still on the main sequence. Also, you mention the size (radius) of the primary as being important for whether or not a disk is formed... however, often the strength of the magnetic field of the primary is much more important, especially in the case of white dwarfs. Sfuerst 19:59, 22 March 2006 (UTC)
- I happily admit the dynamics of these systems is something I never studied. Yes, i was quite vague about the size of a stellar remnant companion, because I wanted to add information for a reader but I didnt want to write a lot (it takes a lot of time to do a good job!). What I meant by 'size' was a combination of mass and physical extent, because that's what determines the actual gravitational equipotential surfaces, the saddle point between the two bodies. If larger (radius) companion overfills its roche lobe (that saddle point determined by the mass of the smaller companion), and is still not in contact with the smaller (radius) companion, then that seems likely to form an accretion disk. That's what I was trying to put into few words, somewhat vaguely. But I agree that ignoring the magnetic fields probably leads to an unrealistic model. As you seem to be more familiar with modeling these systems, please write a better explanation! Myrrhlin 14:01, 24 March 2006 (UTC)
Both of these issues lead me to really question more generally what the tone and direction of scientific articles should take. Should it represent current "traditional" scientific thinking, or a broader spectrum of ideas including largely untested or even unlikely (but still "possible") explanations? In the solar nebula article i edited, there was already a reference to a theory i'd never heard of, which i guess was placed there by a proponent (or perhaps even THE proponent). If a model has little support by the relevant scientific community, should it be included, without a discussion of why it is not accepted as credible? I left it there, not being one to censor anything, and not knowing enough to write anything about problems with it. To be balanced, an article should allow mention of any crackpot theory, but only when a discussion of its failings is also present. Myrrhlin 14:01, 24 March 2006 (UTC)
Conflicting info with Quasar page
This Accretion Disk page says that quasars "can convert about 10 percent of the mass of an object into energy as compared to around 0.5 percent for nuclear fusion processes." However, the quasar page states that quasars "can convert about half of the mass of an object into energy as compared to a few percent for nuclear fusion processes."
The wording of both sentences is identical, just the numbers have changed. One of these has to be wrong, no? I am in no position to say which, but maybe someone smarter than I can clear this up? Patbert 05:48, 9 January 2007 (UTC) patbert
Why do accredition disks form, instead of accretion spheres, or some other shape? This rather basic question is not answered in the article. -- Beland 07:32, 22 April 2007 (UTC)
Well, sounds like a good question, but all you have to do is a little reasoning. All it takes is an understanding about angular momentum. Not that I've ever even taken a physics class before, so I could be absotely wrong, but it seems to me that because the Roche Lobe is tear-drop shaped, the matter being fed into the accretion disk is kinda funneled down into a thin stream, as it is in the pictures. Now, the stream is crazy. Instead of going straight from the companion star to the primary, because they're both spinning, it misses. If you spin in a chair with a friend, try and throw a ball at him or her when you're directly facing them. It's going to miss because the ball will keep its momentum. So that stream misses, but the primary catches it on the rebound. Now the matter's spinning like crazy because it's getting pulled in hard while it spins really fast. So it's being flattened out like spinning a pizza crust in the air, while at the same time being pulled in. Now, keep spinning in that chair of yours. Give one good push, then pull your arms in. You'll notice that the closer you pull in, the faster you spin. That's because the closer you are to the center, the less distance you have to travel, so that same amount of energy will spin you faster. It's what ice skaters do to spin faster without pushing off again. So the matter is pulled in and spins faster, and because it spins faster, it's pushed out. It's like my relationships: the closer you get in, the faster you spin, the harder you're pushed out. The farther you're out, the slower you spin, and the easier you get pulled in. Push and pull, push and pull, lots of friction causing heat between all the particals, until something gives. In the case of a disk, it's thought to be that the streams being shot out at the poles (remember how it doesn't have to move as much when it's close in? It's kinda like being on a merry-go-round in the center where you can stand up) to release the energy of spinning, trying to balance it out, finding the easiest path. And in my relationships, it usually ends in bad memories and a court fee. Either way, it's fun to watch. ElijahD 11:12, 10 May 2007 (UTC)
I added the "confusing" tag right before the "α-Disc Model" section because it comes out of nowhere. More context would be helpful about what attributes of accretion disks are well-understood, and what bulk properties are correctly predicted by gravitional models. Context about the scientific status of the α-Disc Model and the magnetic turbulence mechanism (has it been accepted by scientific consensus? still only a proposal?) is also needed. -- Beland 07:37, 22 April 2007 (UTC)
- I've tried to make the jump less confusing by putting some context and some rearrangement. The MRI explanation is the scientific consensus. Repepo 22:31, 28 June 2007 (UTC)
The mri was actually discovered by Velikhov and Chandrashekar (see mri main article). Perhaps the work of Alfvén is related but the specific mechanism for angular momentum transport is linked directly to the mri. A precise reference to the work of Alfven should be given in any case. Repepo
The external link to Jeong's so-called theory of dipole-gravity has been removed. The terms used and claims made by the author are misleading and confusing. Please refer to Jeong’s contributions at  (Wikipedia:Articles for deletion) to see that Jeong’s model of “dipole antigravity,” which he now refers to as “dipole gravity,” is deemed unfit for Wikipedia, citing serious flaws in his paper. —Preceding unsigned comment added by Djily (talk • contribs) 20:53, 31 January 2008 (UTC)
Dipole gravity literally means two pole gravity. One pole is attractive and the other pole is repulsive. What would you call a repulsive gravity? Antigravity!!! What else?
So, dipole gavity is the same name for dipole antigravity. But Antigravity sounds like a pure Scifi?
Not really. Has it ever occurred to your mind that the jets could be due to the antigravity effect from the rotating core of the galaxies?
If you have a true gravitomagnetism, wouldn't it be like two opposite mass poles that one side is attractive and the other side is repulsive?
That's exactly what is happening in the theory of dipole gravity although it is not even a "theory". It is a self evident general relativity. You have to study it in detail to understand it fully. The paper is available at . —Preceding unsigned comment added by 220.127.116.11 (talk) 11:28, 31 March 2008 (UTC)
"This process can convert about 10 percent of the mass of an object into energy as compared to around 0.5 percent for nuclear fusion processes."
This statement contradicts the mass-energy equivilent article that states that black holes can convert mass into energy, and has it listed under the "perfect conversion" section, insinuating that the process is 100% efficient. ScienceApe (talk) 16:48, 13 June 2008 (UTC)
The intro was recently redone. I reverted the changes because I felt they made it less clear. What's wrong with the current intro, and how can we improve it? -- Parejkoj (talk) 16:28, 12 December 2008 (UTC)
The Binary Star System Image
I don't understand why the black hole is leeching a stream of gas from the star, rather than the entire star just falling into it. —Preceding unsigned comment added by 18.104.22.168 (talk) 20:18, 3 July 2009 (UTC)
- If two stars are orbiting each other, and one collapses into a black hole, the orbit remains the same because the black hole's mass is the same as before.--George100 (talk) 10:16, 4 July 2009 (UTC)
Accretionary Disc and radiation jets suggesting polarity?
Does anyone have more detailed input regarding radation jets. Perhaps we are observing is simply occuring because it could not occur any other way as easily. The jets may just be taking the path of least resistance. —Preceding unsigned comment added by 22.214.171.124 (talk) 18:11, 26 June 2010 (UTC)
Gravitational gradient of super massive black hole
The second paragraph of manifestations says that the gravitational gradient of the black hole is responsible for the friction heating of material, yet super massive black holes have very little gravitational gradient. This apparent contradiction needs to be explained. 2A01:E35:2E68:4F50:FADB:7FFF:FE9E:34E7 (talk) 07:18, 26 June 2013 (UTC)