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The article says 'which is significant because it implies a maximum distance-more distant quasars should be easily observable if they existed' - is this actually the case and can anyone give a reference for that? The z=6.4 quasar was discovered relatively recently in Sloan. If it had been discovered some time ago then I think you could make a case that any more distant quasars would now have been found, but I'm not convinced you can say that now. EddEdmondson 10:40, 18 Jun 2004 (UTC)
Hi, I removed the bit about the highest redshift being significant. I'm an astronomer with the SDSS, the survey that formed the basis for finding these high-redshift quasars, and it's not significant. The only reason there is a maximum to the redshift of known quasars is that it's hard to find them using current telescopes and cameras and analysis techniques. The way the current high-redshift quasars are found is by looking for objects that have only been detected in the longest-wavelength 'z' filter of the 5 SDSS filter passbands u, g, r, i, z. Some of the z-band only detections are just image defects, some are cool stars, and a few of them are high-redshift quasars. They do not have any emission at shorter wavelengths because a) the Lyman-alpha emission line is redshifted into the z-band, and it has the shortest wavelength among the strong emission lines that quasars usually have, and b) because absorption by Hydrogen along the line of sight from us to the quasar is eating up flux. To find even higher-redshift quasars, you would need to extend this 'dropout' technique to even longer wavelengths; however, the quasars get fainter at higher redshifts, and the Lyman-alpha line moves to even longer wavelengths, so that you would need to use a camera that is similarly sensitive as the SDSS camera, but observes at longer wavelengths, and can cover a similar area as the SDSS (it plowed through a quarter of the night sky to find 6 quasars at z>6...). Such a camera doesn't exist yet.
So sometimes the reason that nothing is found is not that there's nothing there, but just that the something is hard to spot even if you know it's there. Higher-redshift quasars will be found eventually. More quasars at the same redshift will also be found eventually. Sebastian Jester
I've updated the quasar with the highest known redshift to be CFHQS J2329-0301, z=6.43, discovery published in December 2007. Apetre ( talk) 02:42, 8 April 2008 (UTC)
This is clearly very OT here... this is the same SDSS guy who wrote the comments about the highest-redshift objects. I checked back to see how the quasar entry had evolved. I want to say that I'm a bit shocked at the incoherence and inaccuracy of the article's content, it certainly has not improved. For example, who cares who thought which quasar was the most luminous if they later turned out to be less luminous? And besides, SDSS has found (or re-found) several quasars that are more luminous than 3C273.
If every wikipedia entry has the same ratio between "what's in the article" and "what an average person who has happened to study the subject matter knows" as the quasar entry, I'm very troubled about how useful the whole thing is. In other words, wikipedia is *a* source of information, but it can never be considered as an authoritative source, because I'll never know whether the latest edit made the entry more accurate, or less.
Of course, I could write a completely new entry that would represent what I think is important about quasars, but if someone else can just edit it back to what it is now, why bother?
Hence, I personally feel it's a waste of my time to contribute anything about quasars to wikipedia because I'd either have to risk that my contribution disappears completely, or have to check back once a week to make sure that nobody has added (obvious or subtle) nonsense. There are more efficient ways to educate the public about your speciality than allowing the public to alter your description of what you know. And there are better ways for the public to learn about quasars than going to wikipedia and hoping that some benevolent person in the know has removed the latest addition of nonsense.
So, please blast me for being off-topic, and off-spirit, but as far as I'm concerned, wikipedia is much ado about nonsense.
Sebastian Jester
The article states that all the quasars that have been found have been very, very far away. Is it safe to assume, then, that all quasars are thus a relic of the early(ish) universe and no longer actively exist? -- Jeffrey O. Gustafson - Shazaam! - <*> 09:20, 6 December 2006 (UTC)
Question from a Wikipedia newbie: The introductory paragraph mentions that Quasars are found in "young" galaxies, but I'm not certain I know what is meant by "young" here. Are young galaxies ones that existed relatively shortly after the big bang, or is youth rather an initial step in the evolution of a galaxy? Is there some property of older galaxies that prohibit Quasar activity, or does the lack of a Quasar itself mark a galaxy as being old? (I'm guessing that we're saying Quasars were a feature of the universe back when there was more matter available to feed the black holes. If so, it would seem that this is more a property of the early universe as a whole, rather than a property of individual galaxies; I'd think that if even an old galaxy somehow bumped into a sufficiently large cloud of gas, it could generate Quasar-level output while consuming it...) Thanks! Jpietrzak ( talk) 00:55, 15 February 2008 (UTC)
How can we see something 28 billion light years away in a 13.7 billion year old universe? Is there proper motion involved or is this a mistake? —Preceding unsigned comment added by 70.135.192.119 ( talk) (transported to the talk page by — Animum ( talk) 16:34, 18 February 2008 (UTC))
I changed the distance to the most distant known quasar from 13 to 28 billion light years, and Fivemack then changed that to 17.4. I admit to knowing nothing about this quasar; all I did was plug the given redshift into Ned Wright's cosmology calculator, click "Flat", and copy the comoving radial distance that it spat out back into the article. Where did the 17.4 Gly figure come from? -- BenRG ( talk) 02:06, 21 February 2008 (UTC)
Based on present day theory, the quasar was about 13 billion ly away when it emitted the light we see, it is now about 28 billion ly away due to expansion. So both answers are correct based on what you mean by 'distance away'. Perhaps it could be made a little clearer. PhySusie ( talk) 17:47, 25 February 2008 (UTC)
Shouldn't the article mention that we kind of have a problem when we find something that is 28 billion ly away in a universe that is estimated to be only about 13.7 billion ly old? Isn't this a current problem in cosmology? -- KarlFrei ( talk) 11:56, 4 March 2008 (UTC)
When astronomers speak of distances to objects in the universe they speak of them in terms of the age of the light that they are receiving. The Universe being only approximately 14 billion years old, could not have observable objects with light 28 billion years old. —Preceding unsigned comment added by Quidproquo2004 ( talk • contribs) 04:54, 2 April 2008 (UTC)
Actually, the distance across the universe is on the order of 90billion light years. In the case of the big bang, the universe was (maybe still is?) expanding faster than the speed of light. Physicists now say that it's ok for something to recede faster than light, but approaching FTL is still forbidden.-- MaizeAndBlue86 ( talk) 11:29, 2 April 2008 (UTC)
Please see KarlFrei's question immediately above yours. It's essentially the same concern. -- Coneslayer ( talk) 12:56, 2 April 2008 (UTC)
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It's a bit scary how many people have been visibly confused by this change to the article. For every reader who edits the article or posts a question here there must be dozens or hundreds who have the same reaction but don't make an edit to show it. Someone also asked about it at the reference desk, spawning this discussion, for which I actually drew a 3D visual aid, reproduced to the right. The brown line is the earth, the yellow line is the quasar, the orange line is the distance to the quasar right now (28 billion light years), and the red line is the path of the light from the quasar to us. The grid lines mark off billions of years and billions of comoving light years. The red line "moves at the speed of light", meaning that it always makes a 45-degree angle with the local grid lines. The way that space seems to curve around into a circle is an artifact of the embedding with no physical significance, and I trimmed it short of a full circle to emphasize that. The pictures are numerically accurate (I calculated the shape from the WMAP data) and you can verify by visual inspection that all of the distances and times come out right. I think these diagrams and the explanation are far too much of a digression for this article, but maybe they'll help someone here on the talk page. -- BenRG ( talk) 10:18, 16 April 2008 (UTC)
Good answer im one of those people. I never edit scientific articles I know far to little about the topics (stick to my own background areas) but it did certainly seem a big contradiction. Thanks for the explaination much appreciated. Kurtk60 ( talk) 23:45, 9 December 2008 (UTC)
Is this because Quasars formed more frequently during the early universe? If so, some more explanatory text about it might be good, including why they formed more frequently in the early universe.
Also, I think I saw figures about the distance of the average Quasar, but I don't recall the distance to the average normal galaxy. beefman ( talk) 19:08, 3 September 2008 (UTC)
You may be able to link to Sołtan argument at this article. 24.199.92.132 ( talk) 08:27, 28 September 2008 (UTC)
Do any quasars presently exist in our universe? Or are all the quasars gone? YouthoNation ( talk) 14:42, 28 September 2008 (UTC)
The text currently shows: "The release of gravitational energy by matter falling towards a massive black hole is the only process known that can produce such high power continuously."
I looked around (including Gravitational wave#Sources of gravitational waves) and I see no mention of it, therefore, I placed a {fact} tag on it for your kind review. Cheers, - BatteryIncluded ( talk) 01:35, 22 October 2008 (UTC)