Wikipedia:Featured article candidates/Cygnus X-1

1) "while the remaining matter may be passing through the event horizon of a black hole." This is not technically true. In the frame of the remote observer it takes infinite time for the matter to reach the event horizon. So the matter is only approaching the event horizon. The same error is in the second paragraph of 'Compact object'.

I'll make it clearer. —RJH (talk)

2) The article says about the supernova II explosion and direct collapse to the black hole. However there is another option: supernova 1b/1c.

Good point. I'll just remove the "type II".—RJH (talk)

3) The first paragraph in 'Jets' says much about potetial energy, but little about angular momentun. The momentun must be carried away (by jets for instance) to make accretion possible.

Okay the text now mentions angular momentum transfer.—RJH (talk)

4) The 'HDE 226868' subsection does not provide a diameter estimate. If it did, it would be evident that the scales in the last figure are wrong, because the size of the disk is much less than the size of the supergiant. The size of the super giant is actually comparable to the semi-major axis.

Yes, the disk probably shouldn't even be visible if it were drawn to scale. I kind of knew that, but unfortunately there aren't many other images to choose from. I'll add a note. Thanks.—RJH (talk) 14:54, 28 April 2008 (UTC)

Is it possible to provide estimates of the radius and luminosity (absolute magnitude) of the supergiant? I suppose they are 40–50 solar radiuses and −7, respectively. Ruslik (talk) 07:10, 29 April 2008 (UTC)

Okay I added some ballpark figures and a justification for the large error range.—RJH (talk)

Does 3-700,000 mean 300,000-700,000? If so, one zero is redundent—700,000 is so high a luminosity! Only some WR stars have smth close to this value. Ruslik (talk) 18:30, 30 April 2008 (UTC)

Yes it does. I'm going by table 1 in Ziolkowski (2005): log(L/Lsun) = 5.46–5.82 for T=30,700, then rounding. But I'm not sure what you mean by a redundant zero, unless you believe it should be 30,000–70,000.—RJH (talk)

I think what I can do is put in a statement like "at the estimated distance of 2,000 parsecs", which would limit the range of possible values. Thanks.—RJH (talk) 14:32, 1 May 2008 (UTC)

I hope my comments will be helpful. Ruslik (talk) 08:52, 28 April 2008 (UTC)

Yes they were very helpful. Thank you.—RJH (talk) 14:54, 28 April 2008 (UTC)

• • I believe I used both. It's an e-print article published by Cornell University.—RJH (talk)
• Current ref 32 "Strohmayer, Tod, Shaposhnikov, etc." What is ESA?
  • European Space Agency.—RJH (talk)
    • Might want to link/expand the abbreviation then. Ealdgyth - Talk 14:49, 28 April 2008 (UTC)
      • Done and done. Thanks.—RJH (talk)

I'd rearrange the lead a little to make it more accessible by placing speculation on how heavy and what it is (i.e. the last sentence of para one) after the first sentence in the lead, before going off into discovery etc.

Done.—RJH (talk)

I'd also state how far the system is away from ours somewhere in the lead nevermind, I did that myself. Cheers, Casliber (talk · contribs) 10:52, 30 April 2008 (UTC)

The Discovery and observation sorta launches into talking about X ray emissions without noting why they might be worth looking for. I know succinctness is the key but an explanatory sentence would be good to frame the significance as a preamble.

I attempted to accomodate this without overly bloating the discussion.—RJH (talk)

With further observations strengthening the evidence, the astronomical community generally conceded that Cygnus X-1 was most likely a black hole by the end of 1973 - I reworded this (as it was ungainly) to the active but you may want to check the meaning. Would this sentence be better after the following two?

The sentences are in chronological order.—RJH (talk)

Fair enough. Cheers, Casliber (talk · contribs) 20:49, 30 April 2008 (UTC)

For this reason, Cygnus X-1 is identified among a class of objects called a microquasar; an analog of the Quasar, or quasi-stellar radio source, now known to be distant active galactic nuclei. - sentence jags from singular to plural, so choose one and make al nouns agree in it. Cheers, Casliber (talk · contribs) 20:49, 30 April 2008 (UTC)

I think it is fixed now.—RJH (talk)

collaminated is a fairly unusual word - I'd wikilink it to a wiktionary or WP meaning or substitute a plainer one. Cheers, Casliber (talk · contribs) 03:19, 1 May 2008 (UTC)

Fixed.—RJH (talk)

In HDE 226868, a mention of the absolute magnitude'd be helpful.

I'm not sure I can do that. The distance estimate has a high margin of error and the magnitude would also need a correction for interstellar extinction, so I don't feel confident that I could come up with an accurate value. In the interest of correctness I'm electing to leave that unspecified. Sorry.—RJH (talk)

Fair enough, I supposed 'supergiant' is at least a succinct term to highlight the star is big and powerful.Cheers, Casliber (talk · contribs) 20:14, 1 May 2008 (UTC)

Actually scratch that. I found a reference that computes the absolute magnitude based on the star's line widths. So that item is complete now. Thanks.—RJH (talk) 20:43, 2 May 2008 (UTC)

In summary, a great choice of topic matter and something that should be on hte main page one day. I think it's nearly there though I do get a niggling feeling some of the middle bits are a bit dry and could be difficult to follow, yet I am unsure how or indeed if they can be written in plainer English without sacrificing meaning. I'll look over the midle again a bit later today. Cheers, Casliber (talk · contribs) 03:33, 1 May 2008 (UTC)

Yes it is a little dry, unfortunately. Some of the data is quite remarkable, at least to me, but I thought it best to stay away from gushiness. =)—RJH (talk) 15:23, 1 May 2008 (UTC)

• • The lead section satisfies the length requirement for Wikipedia:Lead section and it is written to cover the article. Hence it meets the style guidelines. I'm not clear that shortening it by 2/3rds will be beneficial in that regard. Perhaps you could post your prefered lead to the article talk page and we can see whether it satisfies the MoS? As for the references, well that's just the way wikipedia lays them out. The infobox is at the top of the article source text and that's where the numbering starts. I'm not clear why the number ordering should even matter since they are hyperlinked. Thanks.—RJH (talk) 21:01, 7 May 2008 (UTC)

Great idea, I should have started with that. Here's hoping the formatting isn't too messed up:

Cygnus X-1 (abbreviated Cyg X-1) is a compact X-ray source in the constellation Cygnus. It is one of the first black hole candidates to be discovered and is amongst the most studied astronomical objects in its class. As the estimated mass of this object is 8.7 times the mass of the Sun it is sufficiently compact to be a black hole. The X-rays it produces are believed to be the result of matter being stripped from its binary companion, a blue supergiant variable star known as HDE 226868, as its gasses fall toward Cyg X-1 forming an accretion disk and are heated to millions of Kelvin (K) in the process.

This system may belong to a stellar association called Cygnus OB3, which would mean that Cygnus X-1 is about five million years old and formed from a progenitor star that had more than 40 solar masses. If this star had then exploded as a supernova, the resulting force would most likely have ejected the remnant from the system. Hence the star may have instead collapsed directly into a black hole.^[1]

Cygnus X-1 was the subject of a friendly scientific wager between physicists Stephen Hawking and Kip Thorne in 1974, with Professor Hawking betting that it was not a black hole. He conceded the bet in 1990 after observational data had strengthened the case for a gravitational singularity in the system.

I believe this has all of the same information, with the exception of the history, in a more compact form. Details on any of the statements are well covered in the article body, and the specifics don't seem to be required. The history definitely isn't, and follows immediately after anyway. Maury (talk) 21:17, 7 May 2008 (UTC)

Mmm, not quite. In fact it has issues that cause me concern. It does not list the date of discovery, as was requested earlier in the FAC. Mass does not equal density, so the statement about compactness is incomplete. The compact object is not stripping matter from the companion, and it is unclear that the X-rays are caused by the heated gas. It also does not mention the jets, which are key physical features.—RJH (talk) 22:36, 7 May 2008 (UTC)

Ok, simple enough:

Cygnus X-1 (abbreviated Cyg X-1) is a compact X-ray source in the constellation Cygnus. The X-rays it produces are believed to be the result of gasses being heated to millions of Kelvin (K) in an accretion disk around the object, consisting of stellar wind from its binary companion, a blue supergiant variable star known as HDE 226868. A pair of jets arranged perpendicular to the disk is ejecting part of the in-falling material into interstellar space. Estimates place mass of this object at 8.7 times the mass of the Sun and its size at 300 km or less, sufficiently dense to be a black hole. It is one of the first black hole candidates to be discovered and is amongst the most studied astronomical objects in its class.

This system may belong to a stellar association called Cygnus OB3, which would mean that Cygnus X-1 is about five million years old and formed from a progenitor star that had more than 40 solar masses. If this star had then exploded as a supernova, the resulting force would most likely have ejected the remnant from the system. Hence the star may have instead collapsed directly into a black hole.^[1]

Cygnus X-1 was the subject of a friendly scientific wager between physicists Stephen Hawking and Kip Thorne in 1974, with Professor Hawking betting that it was not a black hole. He conceded the bet in 1990 after observational data had strengthened the case for a gravitational singularity in the system.

I believe that addresses the concerns noted above. The only other issue is that it "unclear that the X-rays are caused by the heated gas ", but this is the baseline assumption and has been for the 20 years that I've been following the story. The "minority report" is interesting, but is covered in sufficient detail in the body (ie, one sentence). BTW, if it is reasonable to state that the object is not "stripping" the gasses from the binary, the caption on the image needs to be changed to reflect this. Maury (talk) 03:20, 8 May 2008 (UTC)

Unfortunately your write-up is still ignoring the prior comments made by others in this FAC. It does not discuss the discovery date and method, the distance from the Sun, and it was requested that your last sentence, first paragraph, be placed near the top. I modified the image text and implemented several of your suggested changes. It is more compact now. Thank you.—RJH (talk) 15:08, 8 May 2008 (UTC)