Talk:Quasar/Archive for 2010

References

I came by for the straw poll, and I'm staying for the references. The jstor links just take me to page in the magazine; even if the material is in the page, it needs to be cited with an author, publication, date, etc. The galaxy dynamics link is broken (extra http stuck in there), and it needs to be cited as a journal article, not just a weblink. Not a big deal, but if the article is being cleaned up right now, might as well fix those too! -SidewinderX (talk) 12:59, 13 January 2010 (UTC)

By all means make any changes you feel are appropriate. I'm just cleaning the talk page (it was full of threads from 2004 onwards before I added the auto-archiving). --Christopher Thomas (talk) 18:48, 13 January 2010 (UTC)

Distance (again)

This article needs to either address the "28 billion light years away" question or link to an article or source that does. Looking thru the discussions here, this is something that has come up time and time again. I certainly don't understand this, but I'm hoping someone who does can write up an explanation.

Oh, and I appreciate the diagrams, but the orange is too close to the brown for me to differentiate them. And when you add in yellow and red, I just get lost. Madman (talk) 19:20, 12 January 2010 (UTC)

This is already done in the Overview section, when the distance is first mentioned:

a distance of approximately 28 billion light-years. (N.B. there are some subtleties in distance definitions in cosmology, so that distances greater than 13.7 billion light-years, or even greater than 27.4 = 2x13.7 billion light-years, can occur.)

Short version is, it's the comoving distance, not apparent distance (i.e., where the objects are "now" in our reference frame, vs. where they were when they emitted the light). --Christopher Thomas (talk) 19:51, 12 January 2010 (UTC)

Well, all that N.B. sentence says is that 28 billion light years can occur, reassuring our readers, I suppose, that it's not a typo, but it does not explain it, and the wikilink provided in the article is no help either. In fact, the "N.B." tag probably compounds the confusion since most readers don't understand what N.B. means.

How about if we say something like this?

"This apparent contradiction between the age of the universe (13.7 billion years) and the distance of 28 light years is a result of the expansion of the universe, which can occur faster than the speed of light (see comoving distance for a more complete description of this apparent paradox)."

Madman (talk) 22:26, 14 January 2010 (UTC)

Did you click on the comoving distance link I gave you above? That is the definition of distance being used. I also gave you the short version of the description of it. I agree that this should probably be linked more often from the text, but the link is in the article as well. --Christopher Thomas (talk) 22:38, 14 January 2010 (UTC)

Yes, I clicked on the link. The article is too much to digest now, but I did review it and suggest linking to it in the explanation I offer. How about if we take out that N.B. sentence and insert the one above? Or maybe you can offer an alternative? Madman (talk) 22:44, 14 January 2010 (UTC)

I've adjusted the article to link to comoving distance and to remove the parenthetical description (which didn't seem to actually describe much). --Christopher Thomas (talk) 22:55, 14 January 2010 (UTC)

Straw poll regarding "too technical" template

I did a bit of template cleanup (per exhaustive now-archived discussion, the nature of quasars is no longer controversial). One that I'm unsure about is the "this page may be too technical" one. So, I'm putting this out as a straw poll: Should the template remain, or has the article been made sufficiently accessible to non-experts that it can be removed? Please add a signature and optionally a one-line comment below. Further discussion should probably be in new threads or subsections. --Christopher Thomas (talk) 08:21, 13 January 2010 (UTC)

Still too technical

• There is still quite a bit of unexplained jargon flying around. Most prominently the jargon term "redshift". This makes the article still a bit on the technical side for wikipedia and it could use some work in that area. Lets leave the template. (unless it has been attracting unhelpful edits.) TimothyRias (talk) 10:02, 13 January 2010 (UTC)
• As a reasonably intelligent layperson who understands quasars somewhat, I find this article is still somewhat too technical. I am presently trying to fix one such instance (see Distance (again) above). Thanks, Madman (talk) 22:38, 14 January 2010 (UTC)
• Like user Madman above, I also describe myself as a "reasonably intelligent layperson" with a good general scientific knowledge at a layman's level (and a lot of interest in science and technology). Yet I got lost with this article. It reminded me of the old joke that in order to get a loan you need to prove to the bank that you don't need it, because although the article does give a general idea of what quasars are and how they behave, it seemed to me that in order to fully understand the article as it is, one has to have enough academic training not to need to read a Wikipedia article about this subject. And although user RJHall below opted to abstain, I found that his or her remarks (with which I fully agree) sound more like a "too technical" vote. --UrsoBR (talk) 13:13, 25 January 2010 (UTC)

Not overly-technical

• Christopher Thomas (talk) 08:21, 13 January 2010 (UTC)
• As a non-physicist (but science-savy), I didn't think it was too technical. -SidewinderX (talk) 12:59, 13 January 2010 (UTC)

No opinion/Neutral/Abstain

• The writing varies from easily understood to too technical, so I'm on the fence. I see a few jargon terms used without further explanation. For example: high redshift, relativistic beaming, Schwarzschild radius, accretion disc, absolute magnitude, gravitational energy and Gunn-Peterson trough. I'm not sure that just providing a link is always sufficient because key terms need further explanation in order to advance the article.
  I also see a problem with overlinking on this article; that will need to be trimmed back at some point. :-) —RJH (talk) 17:53, 19 January 2010 (UTC)

Informally closed as "still too technical"

Enough concerns were raised that I think it's safe to say that the template should stay for the time being.--Christopher Thomas (talk) 04:11, 27 January 2010 (UTC)

"Young galaxies" vs. "ancient"

The article states that quasars "tend to inhabit the very centers of active young galaxies" (emphasis added), only to later state that "the implication of the redshift is that the quasars are very distant -- and thus, it follows, very ancient". I know that the latter statement is correct, but I wonder what "young" in the former means and why it ended up there. --UrsoBR (talk) 13:13, 25 January 2010 (UTC)

"Young" means the galaxies were in their early stages of evolution. "Very ancient" means that this stage occurred a long time ago, but we're just seeing it now because of the travel time of light. You could compare Tutankhamun: He was a young king in very ancient times. -- Coneslayer (talk) 13:19, 25 January 2010 (UTC)

I agree with UrsoBR, this sentence seems contradictory. I understand that both of these statements can be true (young, yet very ancient), but I think that the article would benefit from clarifying this point. Eli6 (talk) 22:09, 5 February 2010 (UTC)

I've altered the text to make it clearer. --Christopher Thomas (talk) 22:21, 5 February 2010 (UTC)

"General consensus"

Google reports, Results 1 - 10 of about 3,270 from wikipedia.org for "general consensus". (0.18 seconds).
I have removed the phrase from this otherwise excellent article. Unless Wiki administrators step in, we will need more than Google's 0.18 seconds to deal with the others.
Jerry-va (talk) 14:40, 14 April 2010 (UTC)

"Most luminous, powerful and energetic"?

What about supernovae?

I always learned that supernovae were "the most luminous, powerful, and energetic objects known in the universe", momentarily even obscuring the brightness of whole galaxies, but the article states that quasars are the most powerful. I understand that supernovae are more of a phenomenon than really a kind of object, and that they are a temporary or even momentary event as opposed to quasars, which are objects with a long life that in our common sense and ordinary time scale we could understand as "permanent". Perhaps this is the assumption on which the statement was based, but I suppose many other readers will be puzzled by this question, and it is still not clear which of the two is brighter and more powerful. I believe this should be better explained and supernovae mentioned. --UrsoBR (talk) 13:13, 25 January 2010 (UTC)

Gamma-ray bursts

In addition to the comments made about apparent dyspathy of the article, I would like to talk about gamma-ray bursts. Even on the Wikipedia article (which draws from recognized, well established sources) about gamma-ray bursts, it is said that they are the most luminous events in the universe. Since they are not instantaneous and they affect the universe lightyears away, I believe they could be called "objects." If the rest of the community agrees with me, then I propose the article be changed. Otherwise, I propose we discuss what is considered an astronomical "event" versus "object." -- The Illuminatus (talk) 23:10, 12 May 2010 (EST)

Explain 28 billion light years

"The highest redshift known for a quasar (as of December 2007[update]) is 6.43,[2] which corresponds to a (comoving) distance of approximately 28 billion light-years from Earth."

Would someone please add a sentence explaining how a quasar can be 28 billion light years distant when the universe is only 14.2 billion years old. My understanding is that the most distant objects are only ca. 14 billion light years distant. -- Johnmuir (talk) 06:05, 17 July 2010 (UTC)

This has come up many times before. That is why the word "comoving" is linked in the sentence you quoted. The short, not-quite-right-but-close answer is that the "comoving distance" of an object is where it should be _now_ (in our reference frame), not where it was when it emitted the light we're seeing. --Christopher Thomas (talk) 07:15, 17 July 2010 (UTC)

Thank you. How about that as a footnote as the article on comoving distance (I did look look it up first) is rather unhelpful and is certainly not as succinct as you excellent explanation OR say something like "which is today 28 billion light years from us" OR "which puts it shortly after the Big Bang".

Actually, what point did the author want to make with that information in the first place? Surely it's more important/interesting to date the event rather than say that the remnants (dark and cold no doubt) are today x light years from us.

-- Johnmuir (talk) 12:05, 17 July 2010 (UTC)

I've added a description to the lede of comoving distance, though per threads on talk:comoving distance, it's possible that this article should be calling it "proper distance" instead. I'm hazy enough on the distinction that I'm leaving this for other editors to address. I don't see a good way to add a paranthetical description to this article without cluttering it up; this was tried in the past, and was removed after discussion.

The host galaxies of quasars will look pretty much like normal galaxies, today, rather than being dark remnants. Present understanding is that most galaxies went through an active phase shortly after they formed. As for whether present distance or apparent distance is more useful, the convention used in astronomy (if I understand correctly) is to either quote the cosmological redshift directly (from which these values are derived), or use the comoving distance, so the article follows that convention. I agree that it's fairly arbitrary, but I assume astronomers have a good reason for using it. --Christopher Thomas (talk) 21:09, 17 July 2010 (UTC)

Excellent, thank you. -- Johnmuir (talk) 09:52, 18 July 2010 (UTC)

i'm confuse

"there is now a scientific consensus that a quasar is a compact region in the center of a massive galaxy surrounding its central supermassive black hole"

Is there a quasar at the center or a black hole? —Preceding unsigned comment added by 109.57.38.62 (talk) 10:55, 2 November 2010 (UTC)

The quasar is the brightly-glowing accretion disc and relativistic jets that surround and are powered by the central black hole. This is described in more detail later in the article, and at active galactic nucleus. --Christopher Thomas (talk) 18:56, 2 November 2010 (UTC)