Talk:Supermassive black hole

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[edit] Density

surely the statement that compares denstiy of the black hole to water is not a true statement. I thought black hole was the most dense object in the whole universe?

The density of a black hole is inversely proprtional to the square of its mass. (The radius is proportional to the mass so the volume is proportional to the cube of the mass.) This means that massive black holes are not very dense - and if you plug in the numbers, you get the density of water for mid-range supermassive black holes. Sfuerst 23:18, 30 January 2006 (UTC)

I'm not an expert on this topic, but I'll agree that what he said above definetly makes sense. Also, next time, please remember to sign your name with four tildes (~). Freddie 01:47, 21 February 2006 (UTC)

^That statement about comparing the supermassive black hole to the density of water was mind boggling...it goes against preconceived notions. Is this true for all black holes or just supermassive black holes?

-intranetusa

I understand the maths here but the statement seems to run contrary to the style of the Black Hole article which states "According to general relativity, a black hole's mass is entirely compressed into a region with zero volume, which means its density and gravitational pull are infinite"..."But there is an important uncertainty about this description: quantum mechanics is as well-supported by mathematics and experimental evidence as general relativity, and does not allow objects to have zero size - so quantum mechanics says the center of a black hole is not a singularity but just a very large mass compressed into the smallest possible volume."..."The rest of this article will follow the predictions of general relativity"

So it seems like the statement needs further qualification or at least attention needs drawing to the conflict between general relativity and quantum mechanics relating to this.

If it's true I think it's dead cool haha Dannytrain 14:06, 13 August 2007 (UTC)

The remarks regarding density (above) concern the density within the event horizon (i.e. taking the event horizon as the radius), and have nothing to do with the singularity within. -- Coneslayer 13:56, 14 August 2007 (UTC)
Yes that makes sense. Still a bit weird to talk about 'average density' though I think compared to our everyday notion of density. A layman might assume the density was roughly constant throughout, like most physical objects around us. In this case this assumption is EXTREMELY incorrect. It would imply that when you fell through the event horizon you would hit a wall of air (or matter of air density). But of course as the Black Hole article says, "The event horizon is not a solid surface, and does not obstruct or slow down matter or radiation which is traveling towards the region within the event horizon". Dannytrain 09:54, 17 August 2007 (UTC)
I feel very uncomfortable stating the density of the black hole was very low. That sounds ridiculous if you keep in mind, that the density of a neutron star is very high and a black hole is a neutron star that increased it´s density. You cannot simply take the event horizon as the black hole itself. Event horizon is one thing, black hole is another. You can say, the density within the event horizon is low, but saying the black hole has low density is not very sensible in my opinion.Maradona01 10:20, 4 December 2007 (UTC)
My (amateur) understanding is that black holes of the same mass are indistinguishable from one another, and thus it is impossible to know the radius or composition of the actual mattery part--only the mass and the size of the event horizon. So realistically that part is probably, yes, very very dense, but it could be a sphere of water the size of the event horizon, and we'd never know. Anyway, do physicists actually refer to the density in this way? It sounds like the kind of thing that professors would trot out once a year to baffle or impress their students; if so, I'd consider it out of place in an encyclopedia article, at least in the first section. Dzhim (talk) 23:46, 30 May 2008 (UTC)
Right. The issue can be resolved by being clear about the definition of "black hole", which is really more than just the point singularity at the center (which is completely unobservable), but includes also the surrounding region, at least as far as the event horizon. Assuming general relativity applies at the singularity (in spite of the conflict with quantum mechanics), the density at that point would simply be infinite, and zero (or nearly zero) elsewhere. But the average density  inside the event horizon does seem to decrease with mass, because the radius increases proportional to the mass, being basically 3 km per solar mass, and the volume (at least, naively computed for a Euclidean sphere—which it ain't) increases like r3, so the mass divided by this "apparent volume" does decrease as the mass goes up.
I think physicists generally do not refer to the density, as you inquired, without qualifying it, perhaps as "average density", but that key qualification easily gets lost on non-expert listeners.
One of the reasons the argument for the existence of black holes is so compelling is that it does not depend on the mysterious nature of the singularity, it only depends on the geometry of the exterior region, from the event horizon on out, and conditions there can be quite ordinary. In fact, if it had turned out that we live in a closed universe (a notion lately out of fashion, but still possible I think), then we would in fact be inside the event horizon of a huge black hole, falling towards the inevitable singularity (billions of years in the future), and the average density would be a few proton masses per cubic meter. Wwheaton (talk) 01:59, 31 May 2008 (UTC)

[edit] significance

I'm very interested in supermassive black holes in relation to galactic life cycles...supposedly primordial black holes cause galaxies in nebulae, rather than galaxies causing black holes, or something, since it could "spark" the formation of stars? Can the article shed light on this? -- Natalinasmpf 14:33, 16 Apr 2005 (UTC)

The most accurate current theory of galaxy (galaxy cluster) formation uses dark matter as the gravitational source. Primordial black holes (unless they are so numerous that they are the source of dark matter) don't fit very well, and I haven't seen them seriously suggested for this in quite some time. Star formation is something different entirely - there the problem is one of cooling rates. Primordial gas cools very inefficiently, so finds it difficult to collapse, and black holes don't help there either. In short - perhaps that belongs in an article on primordial black holes, but not this one. Sfuerst 23:18, 30 January 2006 (UTC)


[edit] Mass?

Supermassive black holes can range from 1000000 to 10000000000 stellar masses.

Half right, the limits should be a few times 10^5, to a few times 10^10 (not 10^9 as I put before), I'll fix the article. Sfuerst 23:18, 30 January 2006 (UTC)

Just to be clear, is Stellar mass the same thing as solar mass? I cannot find an article on it.--Doom Child 07:19, 21 February 2006 (UTC)

Stellar mass is ambiguous, surely. Solar masses are clearer :P HawkerTyphoon 00:22, 30 August 2006 (UTC)


Somebody messed up the formatting of the whole first section, which I fixed. There was a snippet of code I didn't know what it did (I'm new here), so I took it out since it was incomplete and therefore not doing anything. Here it is, if anyone wants to reconstruct it and put it back:

releases/press_111902.html Chandra Press Room :: Never Before Seen: Two Supermassive Bl Holes in Same Galaxy :: November 19, 2002]</ref> holes==

Might be a citation for the mass figure (that's what it was after...), but I don't know citation syntax. Daniels220 (talk) 00:37, 18 May 2008 (UTC)

[edit] Size

What is the theorized physical size of the Super Massive black hole at the center of our Galaxy? I have gone the article and I don't think I have missed it. Thanks. Doom Child 04:58, 18 February 2006 (UTC)

You assume that the Milky Way has one in its center? It is currently thought that it could contain one, but going from such a theory and not having observed one, to wondering about its size, I think is a bit of a stretch. Even moreso if it would be included in the article. I have to wonder if it would just be confusing to readers if it started listing theoretical sizes for theoretical black holes, giving a false sense of credibility. My opinion here would be -- first direct observations, then estimates. -- Northgrove 16:06, 27 July 2006 (UTC)
The black hole at the centre of the Milky Way (associated with Sagittarius A*) is estimated to have mass equivalent to about 2.6 million times that of our Sun, based on the motions of stars near it. That gives it an event horizon radius of about 8 million kilometres (0.05 AU). --Christopher Thomas 04:37, 19 August 2006 (UTC)
It's a little more than theory Northgrove, there is significant evidence that there is in fact a supermassive black hole at the center of our Milky Way galaxy and at the center of most if not all spiral galaxies that resemble ours. What's debatable is whether it is currently active or not. —The preceding unsigned comment was added by 12.24.60.12 (talk • contribs) on 22:17, 29 August 2006.

[edit] Disambiguation page needed?

The last sentance of this article:

""Supermassive Black Hole" Is also the title of the first single from Muse's new as of yet untitled fourth studio album."

is completley out of place with the topic of this article. I'm torn whether there should be a disambiguation page or just delete this sentance. Annyone have any thoughts? Ed 15:43, 30 April 2006 (UTC)


This was added very recently, it looks like, and I'm not sure that a single deserves an article of its own... I'll just delete the sentence. Hbackman 23:45, 30 April 2006 (UTC)

As a Muse fan I think it does. After all, who knows how many of them might get turned on to astrophysics by this populist usage? Royzee 10:45, 17 May 2006 (UTC)

My guess is that it's equivalent to the number of photons that can escape a supermassive black hole.

I don't think it's needed, especially because the album hasn't even been named yet. If, in the future, the single itself is notable enough to have its own article, then a disambig statement in the beginning of the article or a Supermassive black hole (disambiguation) (with link) may be appropriate, but until then, I don't think it's needed at all. --Deathphoenix ʕ 13:56, 19 June 2006 (UTC)

[edit] Eddington limit

As a non-physicist I was wondering if the article's explaination of how SMBHs can form has kept up with the latest thinking. From what I can gather the 'slow accumulation' hypothesis has been problematic because at a certain rate the energy from the accretion disk causes it to be blown out - starving the BH of material. The New Scientist article suggests an exotic mechanism by which this limit could be overcome. However, I'm not competent to make any changes. Maybe an expert could help.--Ekilfeather 15:39, 12 July 2006 (UTC) http://www.newscientistspace.com/article/dn9530-earliest-black-holes-bent-the-laws-of-physics.html

[edit] Typical event horizon?

How large is the typical event horizon of a supermassive black hole? A graphic putting it on a scale against our solar system (or whatever would be appropriate) would be nice.


I would like to know this too, because it's hard to imagine that an astronaut could stand on the event horizon, and not experience any significant tidal force. If that's the case, how can these black holes devour other stars in other solar systems? They can suck up stars, but not astronauts standing on their event horizon? That doesn't sound like it makes a lot of sense. Malamockq 17:07, 16 August 2006 (UTC)
Supermassive black holes range in mass from on the order of 1 million to on the order of 1 billion times the mass of our Sun. This gives a radius of on the order of 0.02 to 0.2 20 AU. An astronaut falling into a supermassive black hole wouldn't feel significant tidal forces, for the reasons described in the article. However, they're most definitely still falling _in_. Absence of tides just means the different parts of the astronaut are falling in at approximately the same rate (see tidal force for details). --Christopher Thomas 04:40, 19 August 2006 (UTC)
At what acceleration would they be falling in (approximately)? For example, on Earth the gravitational acceleration is 9.8 m/s^2. Also your estimate of the event horizon seems to contradict statements on wikipedia. I recently found this page, http://en.wikipedia.org/wiki/Q0906%2B6930 which states that the event horizon is 1000 times the solar system. Malamockq 15:00, 21 August 2006 (UTC)
The radius information at Q0906+6930 is approximately correct. Per the correction above, I should have written 20 AU, not 0.2 AU, for the billion-solar-mass black hole. At 10 billion solar masses, Q0906+6930 would have a horizon radius of 200 AU, or about 6.7 times that of Neptune's orbit, making the volume enclosed about 300 times that of the solar system (the article you link states an enclosed volume 1000 times that of the solar system, not a radius 1000 times greater). The formula for event horizon radius is given at Schwarzschild radius, which gives answers that agree almost perfectly with my estimates. --Christopher Thomas 15:23, 21 August 2006 (UTC)
No, the reference states the SMBH can hold 1000 of our solar systems. http://www.space.com/scienceastronomy/heavy_blazar_040628.html 65.40.195.176 05:59, 3 March 2007 (UTC)
Your link points to an article in popular literature, not scientific literature. Its numbers are more or less pulled out of a hat (you'll notice that they're all powers of ten). For accurate radius and volume numbers, check the original paper by the researchers who discovered the hole, or plug the estimated mass into the Schwarzschild radius equation yourself (though the "10 billion suns" mass estimate is probably about as inaccurate as the "1000 solar systems" value, given the source). --Christopher Thomas 07:40, 3 March 2007 (UTC)
The journal source on that wiki page gives a similar mass estimate at, greater than 10^10. I wouldn't say that's pulled out of a hat. Do you have the original paper by the researches? I'd like to see what they say about it's volume and radius. 64.236.245.243 14:30, 8 March 2007 (UTC)
I am not your secretary. Five minutes on google with the information in the Science article pulls up the paper draft; please do your own googling in the future. The mass given is 1010.2 solar masses, or about 16 billion, without error bars (estimate performed on page 2). To estimate the error bars, look at the calculation. The Hubble constant used is 71 km/sec/Mpc. The Hubble constant is only known to within 5-6% from the WMAP data. This is used to compute the luminosity, which in turn is directly used to compute the mass, introducing an error of about 8% (dependence of luminosity on distance is quadratic, and that term is raised to the power of 0.7). The other part of the term depends on the square of the spectral width of the line used in identification, with has an uncertainty specified of about 10%, giving a contribution uncertainty of about 20%. Combining these (independent) uncertainties gives a final uncertainty of around 22% (independent sources of error don't stack as badly). So, it's about 16 billion with a standard deviation of around 3.5 billion.
There are no numbers at all given for radius (or volume) of the black hole in the paper. It is described as being a "point source", with VLBI radio data being used to attempt to resolve the jets emitted by the galactic core.
Plugging the mass estimate into the Schwarzschild radius formula gives a radius of about 4.8e+13 m, with the same roughly-20% error as you have with the mass. The semi-major axis of Neptune's orbit is about 4.5e+12 m. This gives a volume for the black hole of about 1060 times that enclosed by Neptune, with an uncertainty of roughly 60% (cubic dependence on black hole radius). Plugging in one-deviation-off numbers for mass gives a volume of anywhere from 600 to 2100 times that enclosed by Neptune.
Per my previous statement, the article in "Science" just picked powers of ten that were close to each value. --Christopher Thomas 16:29, 8 March 2007 (UTC)
You aren't my secretary, but don't give me attitude. It was a humble request, because I don't know the whereabouts of such things. The links on the wiki entry indicate you need to be a registered user to see the journals.
So in other words the volume can be 600-2100 times Neptune's orbit. Thank you for the clarifications, although it shows that your earlier estimations were indeed wrong. 64.236.245.243 16:46, 8 March 2007 (UTC)
There is a web site called "Google" that is very good at _finding_ the whereabouts of such things. This is, in fact, exactly how _I_ found it. Additionally, your challenging of my correctness would be more plausible if your original position hadn't been to assume correctness of two numbers (10 billion solar masses and 1000 volumes) that were incompatible with each other according to General Relativity. You'll forgive me if I don't take your complaint very seriously. --Christopher Thomas 17:03, 8 March 2007 (UTC)
I find it amazing, and also sad that you seem to be more concerned about saving face, and denying that you were wrong instead of discussing the topic at hand. I don't think anyone here really cares if you were wrong. That's besides the point, getting acurate numbers for the article is more important.
And about your irrelevant diatribe (which we shouldn't even be discussing), yes I'm well aware of google, but I assumed scientific journals would not be found on it if the links on the wiki article required some kind of registered user log in. Since you are so keen to demand scientific journal references, I expected you to have them on hand. If you are going to demand them from other people, you should also be expected to do the same. 64.236.245.243 17:45, 8 March 2007 (UTC)
What part of "a 10 billion solar mass black hole encloses a volume about 300 times that of the solar system" are you claiming is incorrect, precisely? If you take space.com's mass figure as correct, you get this volume. If you take their volume figure as correct, you get a different mass than the one they quoted. --Christopher Thomas 21:14, 8 March 2007 (UTC)
I'm not saying your math is wrong, but your previous estimation of Q0906+6930's volume was drastically different than what was stated in the article's text. Therefore your estimated volume for Q0906+6930, was incorrect. Your new estimations are more in line with what the text states. 64.236.245.243 21:28, 8 March 2007 (UTC)
You appear to be missing the point. If you assume the volume is correct, the mass stated is wrong. If you assume the mass is correct, the volume stated is wrong. I pointed out that these numbers were inconsistent, and gave what the volume would be if we pretend that space.com had the mass right. You believed _both_ of these numbers, so why exactly are you faulting me for taking (an arbitrarily picked) _one_ of them to be correct? --Christopher Thomas 22:08, 8 March 2007 (UTC)
I never really mentioned anything about the mass, just the volume which space.com quoted from actual researchers. They simply estimated 10 billion solar masses without realizing how much of an impact it would make on the volume if they were off by a few billion. Like you said, they just wanted a round number. But the article is correct now so who cares? 64.236.245.243 15:01, 9 March 2007 (UTC)
As for infalling acceleration, that depends very much on how you choose to measure distance and time. This is discussed somewhat in the talk archives of black hole. To a distant observer, the infalling astronaut seems to slow down, flatten, and stop before touching the horizon. If the distant observer tries to take rigid rods and measure the distance to the infalling astronaut, keeping the rods stationary with respect to some distant point, they find that the event horizon seems to be an infinite distance away and the astronaut seems to be accelerating indefinitely (reaching speeds arbitrarily close to C and arbitrarily high kinetic energies). Because distance and time can be mapped onto curved spacetime in different ways, you end up with different answers for acceleration depending on how you choose to measure it. --Christopher Thomas 15:23, 21 August 2006 (UTC)

[edit] The first stars?

I read that the very first stars were unbelivably massive, much bigger than the biggest blue giant today. Is it possible that when these stars burned out, they became supermassive black holes? —The preceding unsigned comment was added by 76.185.18.21 (talk • contribs) 3 December 2006 (UTC)

I think Population III stars are generally thought to have been on the order of hundreds of solar masses, not the millions to hundreds of millions of solar masses that SMBHs are. Do you have a specific source putting their masses in the same range? -- Coneslayer 23:44, 3 December 2006 (UTC)

[edit] Vandalism Spotted

First line..."God's Penis" and stuff like that...please revert to appropriate language version.

[edit] Light in a black hole

What happens to all the light trapped in the black hole? Are black holes invisible without special X-ray light —The preceding unsigned comment was added by 69.183.241.178 (talk) 16:00, 26 February 2007 (UTC).

There is no way for light to orbit stably within a black hole (the critical radius is outside the hole), so what happens is the same thing that happens to matter: the path of the light beam is warped so that it's pointing towards the singularity, and it eventually hits it. While better models of black holes may change our views of what goes on inside them, as far as an outside observer is concerned the light is just absorbed, and adds to the black hole's total mass.
Black holes aren't "invisible"; they just appear almost perfectly black. There's an extremely faint glow due to Hawking radiation, but it's faint enough to be almost unobservable. The hole's effect on its enviroment can be observed. It bends the path of light that passes near it (gravitational lensing). If the black hole is absorbing matter, this forms a dense, hot accretion disc that emits lots of light, and typically results in polar jets whose interaction with the local environment shows up strongly in radio waves. --Christopher Thomas 07:26, 3 March 2007 (UTC)
So the concept drawings of black holes are relatively acurate of how they would really look like? 64.236.245.243 17:50, 8 March 2007 (UTC)
Depends on the drawing. You'd only see a black circle if you were very, very close, and you'd see distortion of the background view if you were that near it (example: Image:BlackHole_Lensing_2.gif). A black hole that was drawing in matter would be dwarfed by the very bright accretion disc and jets around it (Image:Accretion disk.jpg shows a hole that's much too big, but is otherwise correct). Did you have specific pictures in mind? --Christopher Thomas 21:11, 8 March 2007 (UTC)
Yea, those pictures I thought of. The color of the accretion disc would be blue? 64.236.245.243 21:42, 8 March 2007 (UTC)
The accretion disc will be glowing with a black body spectrum (it's a hot object, heated by friction within the disc). The parts glowing most brightly would appear blue-white to the naked eye (hotter areas emit far, far more light than colder areas, even if they're smaller). --Christopher Thomas 22:02, 8 March 2007 (UTC)
So it's brighter than the sun (the accretion disk)? 64.236.245.243 15:03, 9 March 2007 (UTC)
It's _hotter_ than the sun. Whether or not it's _brighter_ depends on how much mass is falling in. --Christopher Thomas 16:35, 9 March 2007 (UTC)


[edit] Need edit?

The following section illistrates why I hate my physics text book: There appears to be a link between the mass of the supermassive black hole in the center of a galaxy and the morphology of the galaxy itself. This manifests as a correlation between the mass of the spheroid (the bulge of spiral galaxies, and the whole galaxy for ellipticals) and the mass of the supermassive black hole. There is an even tighter correlation between the black hole mass and the velocity dispersion of the spheroid. The explanation for this correlation remains an unsolved problem in astrophysics.

It may be just me but this sounds like it could use some tweaking:

smaller words(wikipedia needs to be as understandible to the 6th grader as it is to the professor).
add links(suggest: morphology, spiral galaxies, ellipticals).
example pictures would be nice.
Otherwise good.

--Wilson 18:50, 16 March 2007 (UTC)

[edit] =Creation of Galaxies

I'm scrapping this section as it's unworkable in its present form. Badly cited, not encyclopedia style, and really pretty close to original research. It may be salvageable by someone willing to completely rewrite it, so feel free to give it a shot if so inclined. But it would be a disservice to leave it in as it is. Vonspringer (talk) 08:41, 15 February 2008 (UTC)