Talk:Supermassive black hole

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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)

Contents 1 significance 2 Mass? 3 Size 4 Disambiguation page needed? 5 Eddington limit 6 Typical event horizon? 7 The first stars?

[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)

[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)

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)