Talk:Cygnus X-1

message: "The mass of the supergiant is approximately 20–30 solar masses. The compact object has a mass of 7–13 solar masses ... The X-rays are produced in an accretion disk that is formed by matter flowing from the supergiant into the black hole."
If the star is more massive than the black hole, why is matter flowing away from it? Evercat 12:48, 28 July 2006 (UTC)
replies: text: The deciding factor is density, not mass. -Toptomcat 22:30, 20 September 2006 (UTC)
thread_title: Mass

message: What does "Musical Connections" have to do with this subject?
I see absolutely no reason for the entire section.
Possible reason: people may get to this page by searching for information on the Rush song.
:Some people seem like to adding cultural influences into scientific articles such as these. (See stars and planetary systems in fiction, as an example.) Unfortunately they can be a nuisance to properly cite, so they often end up being moved elsewhere. As a possible solution, the section could be moved to a disambiguation page.—RJH (talk) 19:42, 17 March 2008 (UTC)
replies: text: Done.—RJH (talk) 18:26, 29 March 2008 (UTC)

text: See Cygnus X-1 (disambiguation). I didn't want to deal with all the unsourced material that is only indirectly related to the subject matter. Plus the cultural influence seemed quite trivial when compared to that of the planets and some brighter stars.—RJH (talk) 21:01, 5 May 2008 (UTC)
thread_title:  Musical Connections 

message: Hi RJH, I just hit an edit conflict with you in this section.  I have copied the subsection as I had it below; use it any way you want. 
Though highly and erratically variable, Cygnus X-1 is typically the brightest persistent source of hard X rays—those with energies from over about 30 up to several hundred keV—in the sky.   The compact object is believed to be orbited by a thin, flat disk of accreting matter. This disk is intensely heated by friction between plasma in faster-moving inner orbits and that in slower outer ones.  It is divided into a hot inner region with a relatively high level of ionization, and a cooler, less ionized outer region that extends to an estimated 500 times the Schwarzschild radius, or about 15,000 km. The X rays are produced as lower energy photons in the thin inner disk, then modified by Compton scattering from very high temperature electrons in a geometrically thicker, but nearly transparent corona enveloping it, as well as by some further reflection from the surface of the thin disk. An alternate possibility is that the X rays are Compton scattered in the base of a relativistic jet instead of in a hot corona. 
Cygnus X-1 changes unpredictably between at least two X-ray states, although it may vary continuously between those states as well. In the most common state, the spectrum is "hard", and more of the X-rays have high energy. In the less common state, the spectrum is "soft", with more of the X rays having lower energy. The soft state also shows greater variability. The hard state is believed to originate in the hot corona surrounding the inner part of the more opaque thin accretion disk. The soft state occurs when the inner disk draws closer to the black hole (possibly as close as 150 km), accompanied by cooling or ejection of the corona. When a new corona is generated, Cygnus X-1 returns to the hard state.
The X-ray flux from Cygnus X-1 varies periodically every 5.6 days, especially during superior conjunction when the orbiting objects are most closely aligned with the Earth, and the compact source is most distant. This indicates that the X-ray flux is partially blocked by circumstellar matter,  possibly the strong stellar wind of the star HDE 226868. There is also a roughly 300 day periodicity in the emission that may be caused by the precession of the accretion disk.
Cheers, Bill Wwheaton (talk) 23:40, 2 April 2008 (UTC)
replies: text: Thank you. I think I managed to merge in your changes.—RJH (talk) 15:09, 3 April 2008 (UTC)
thread_title:  Accretion disk 

message: "As self-luminous clumps of matter spiral into a black hole, their radiation will be emitted in a series of pulses that are subject to gravitational redshift as the material approaches the horizon. That is, the wavelengths of the radiation will steadily decrease, as predicted by General Relativity."
Surely the radiation wavelength will increase, not decrease, if it is redshifted?
Gburto01 (talk) 15:00, 3 April 2008 (UTC)
replies: text: You are correct of course. Thank you.—RJH (talk) 15:10, 3 April 2008 (UTC)
thread_title: Gravitational Redshift

message: I may not be following, but the article seems to shift back and forth between "a [probable, possible] black hole" and "the [certain] black hole".  I might be missing something. - Dan Dank55 (talk) 20:33, 11 April 2008 (UTC)
replies: text: Overall I was trying to avoid the position of 100% certainty, even though the evidence is fairly strong. But it seemed a little awkward trying to say something like, "the remaining matter is believed to pass through the event horizon of the possible black hole". I.e. in order to pass through a event horizon, there must be a black hole present. Having the word "believed" in there seemed to be sufficiently cautious.—RJH (talk) 21:39, 11 April 2008 (UTC)
replies: text: I agree with the position that certainty of Cyg X-1's nature should be avoided. --Stlemur (talk) 22:19, 11 April 2008 (UTC)
replies: text: This seems like an interesting question to me: under what circumstances is "the" a word to avoid?  It's not mentioned at WP:WORDS, which is relevant here because it's one of the 6 specific style requirements that GAN articles are supposed to pass.  I've asked on the talk page there. - Dan Dank55 (talk) 22:52, 11 April 2008 (UTC)
replies: text: I made some modifications to the text that I hope will address your concerns. Thank you.—RJH (talk) 15:06, 13 April 2008 (UTC)
replies: text: Elegant edits, that does it nicely.  That gave me some nice food for thought which I hope will lead to people accepting my proposed changes to WP:WORDS.  I'm not your GAN reviewer btw, or at least, I'm not available until May 1, it might bias the survey if I start telling people what I like and I don't like. - Dan Dank55 (talk) 19:44, 13 April 2008 (UTC)
replies: text: No problem, I appreciate the feedback. Thank you.—RJH (talk) 14:48, 14 April 2008 (UTC)
replies: text: My pleasure. - Dan (talk) 21:06, 15 April 2008 (UTC)
thread_title:  Some style questions 

message: *Does Cygnus X-1 refer to both the black hole and the star system? And is the x-ray source the compact object by itself or the combination of both the black hole and the star?  The article uses Cygnus X-1 to refer to both but it's never explained. Also, in the lead, you define Cygnus X-1 as a compact X-ray source  I take it you mean the binary system and not the black hole itself (it's not immediately clear)?
** I've tried to modify the text to specifically say "HDE 226868/Cygnus X-1" when it is talking about the binary system as a whole. By "Cygnus X-1", the text just means the candidate black hole.—RJH (talk)
*I had trouble understanding the paragraph bellow, is it corroborating with the assertion that Cygnus X-1 is a black hole or not? I can't tell.
*:The space-based Chandra X-ray Observatory was used to measure the spectral signature of iron atoms orbiting near the object. A rotating black hole drags the nearby space around with it, which allows atoms to orbit closer to the event horizon. In the case of Cygnus X-1, none of the atoms were found orbiting closer than 160 km, indicating that, as a candidate black hole, it is not rotating to any significant degree.
*::It is saying that, if this is a black hole then it is not rotating. I'm not sure at present how that could be made clearer.—RJH (talk)
:::: Thanks for adressing the issues I raised so quickly, about this paragraph I had indeed understood that it was not rotating, I think my confusion arose from the word candidate, I assumed from its presence there, that the rotation or not of x-1 had some bearing on its chances of being a black hole (ie: if its rotating then chances are its a black hole or vice versa) But it could just be me. Again thank you for your work Acer (talk) 19:35, 27 April 2008 (UTC)
replies: text: Rockets and balloons were widely used in the early days before satellites.  Shorter wavelengths than ultraviolet light have greater penetrating power, and get deeper in the atmosphere.  X rays of a few keV energy easily penetrate to altitudes reached by sounding rockets, and Cygnus X-1 is so strong that it can be detected in a few seconds even by small instruments on such probes.  X rays of energy higher than 20 keV can be observed from instruments carried on balloons to altitudes as low as 35 or 40 km.  Cyg X-1 is very powerful from 20 to 500 keV.  Wwheaton (talk) 06:11, 28 April 2008 (UTC)
replies: text:  Much of this would be good information to include in the X-ray astronomy article.—RJH (talk) 21:19, 28 April 2008 (UTC)

text: Thank you very much for your help and your input.—RJH (talk) 19:16, 27 April 2008 (UTC)
thread_title: Comments

message: Hi, RJH -- In the section on "Jets", you suggest most of the accretion energy is dissipated in jets.  I wonder if that is  really true.  First of all, a lot comes out in radiation; I think the x-ray and gamma-ray luminosity is on the order of a few times 1036 erg/s if I recall. (I see that you quote tne energy in the jets of being at least of the same order.) Second of all, a lot of the energy probably goes down the hole and disappears from view.  It would be very interesting to have some numbers, or likely ranges, for this energy balance.  Also interesting would be the likely amount of mass lost from HD226868 that is actually accreted.  The artist's impression figure looks like Roche lobe overflow, and in that case I guess the fraction could be nearly 100%, and the accretion energy would simply be the mc²  limit.  But for mass loss via a stellar wind, the fraction could be smaller, I don't know how small.
The efficiency of black holes conversion of accretion energy into released energy (radiation, jets, etc) has been a question for decades I think, and I do not know how much progress we have made on the issue lately.  But it seems fundamentally interesting to me that, as similar as BHs may appear to some neutron stars, yet they do not have to conserve energy in the same sense, because they can stash an unlimited amount by dropping it down the hole.  Whatever is known about this for Cygnus X-1 would be most interesting to put into the article, and it seems to me that after all the work you have done you may be a good person to know the story.  
Anyhow, as a practical matter (which is what brought me here in the first place), I think you might do well to change the "Most of" [this released energy] to "Some fraction of", unless you know the answer, which you may.
Continue to be delighted by what you are doing.  Cheers, Bill Wwheaton (talk) 18:52, 1 May 2008 (UTC)
replies: text: Good point. I changed "Most" to "Part". The sources suggested that roche lobe overflow was not occurring. Perhaps the illustration is exaggerating the matter flow slightly? I don't think I've seen a good source for how the energy is being distributed; I'll look around some more. Thank you.—RJH (talk) 20:58, 5 May 2008 (UTC)
thread_title:  Accretion efficiency? 

message: Here's what I hope is a compromise modification to the lead:
:Cygnus X-1 (abbreviated Cyg X-1) is a strong X-ray source in the constellation Cygnus. It was found in 1964 during a rocket flight and is one of the strongest X-ray sources seen from Earth, producing a peak X-ray flux of 2.3 Wm-2Hz-1. Cygnus X-1 was the first X-ray source widely considered to be a black hole candidate and is amongst the most studied astronomical objects in its class. It is now estimated to have a mass about 8.7 times the mass of the Sun and has been shown to be too compact to be any known kind of normal star or other likely object besides a black hole. If so, the radius of its event horizon is probably about 26 km.
I felt that the "It was one of the first X-ray sources found" was outweighed by the "Cygnus X-1 was the first X-ray source widely considered to be a black hole candidate", so I snipped out the former for purposes of flow and brevity. Hope that's okay. I also listed a maximum flux rating with the understanding that it can be expanded upon in detail down in the article body.
Will this work?—RJH (talk) 18:42, 16 May 2008 (UTC)
thread_title: Proposed lead

message: The link to the main article the "Stephen Hawking and Kip Thorne" goes to  "Thorne-Hawking-Preskill bet"
As far I can tell, it doesn't seem to be the same bet.
I removed the link.  —Preceding unsigned comment added by Curtis95112 (talk • contribs) 10:39, 26 June 2008 (UTC)
thread_title: Incorrect Link

message: Is the caption of this image correct? This  gives the impression that it is an actual Hubble telescope image, rather than a drawing.
--PeR (talk) 15:07, 26 June 2008 (UTC)
replies: text: It's artwork that originated from the ESA/Hubble groups. There are only a handful of stellar disks that have been resolved by Hubble. (Betelgeuse for example.)—RJH (talk) 15:12, 26 June 2008 (UTC)
replies: text: Is this really an accurate model?  I can't understand why the surface of the blue giant would be nice and round except for one huge horn pointing up, when that end really isn't much closer to the hole than the areas near it. Wnt (talk) 18:24, 26 June 2008 (UTC)
replies: text: Hard to say.  The standard picture for Roche lobe overflow accretion would be for the donor to have a convex teardrop shape with the point directed close to the recipient, and maybe a sharper photospheric edge.  That would be "right" for a low-mass, older star trying to expand to become a red giant but overflowing through the L1 Lagrange point.  But HD 226868 is a massive young O/B star, and these usually have a powerful stellar wind (in all directions I suppose), a part of which then accretes from the part of the wind that can be caught by the compact source.  HD 226868 seems more massive than the BH, so its Roche lobe should be the larger, and the L1 point ought then to be closer to the BH than to the center of the star.  See Wolf-Rayet star for an actual image of an extreme case of a massive wind--very messy.  The artist may be trying to capture an intermediate case, or maybe just equivocating between the two to cover the bases of uncertainty. Wwheaton (talk) 19:17, 26 June 2008 (UTC)

text: If you ignore the stellar wind, then the core stellar body seems to shows the proper oblate shape. Not sure if it's precisely correct though. Per the article, the stellar wind is focused, so there is some overlap. So it seems roughly correct. Section 4.1 of Miller et al (2005), has a diagram of the wind geometry. There was an outline of the star's gravity-distorted profile in one of the sources, but I can't seem to dig that up right now. Anyway, my $.02 worth.—RJH (talk) 20:14, 27 June 2008 (UTC)
replies: text: I don't really understand how the "messy" structures form, and I'm not sure why stellar wind material would have a shape different from what a larger star would take on.  Meanwhile, I've looked through several Google Image results for "Roche lobe", and there seems to be quite a range of artistic opinion about the shape of the "horn".  Many show it as convex, sometimes even to the point of being rounded; others show it as a precise cone; a few show it like this, appearing to rise up in a slender filament with a concave surface.   NASA has a picture with a convex (but irregular) horn.   To do some very crude "OR" I made up a spreadsheet with the formula "=1000/(SQRT(($A11-7.5)^2+(L$22-7.5)^2))+1000/(SQRT(($A11+7.5)^2+(L$22+7.5)^2))" and rows of numbers to the left and bottom, which tells me that for equal masses, the gravitational potential at the central point is slightly higher than at any point along a straight diagonal line (i.e. a row or column of the spreadsheet), which I take to mean the horn should be very slightly convex ... it isn't much of a physics simulation though, since it omits the mass concentration of the horn itself or the effect of rotation. Wnt (talk) 13:33, 29 June 2008 (UTC)
replies: text: It's the best picture we've got for right now. Perhaps a future computer simulation will be an enhancement. But for the moment I think it gets the general layout across, and it's acceptible for it's aesthetic value as well.—RJH (talk) 15:04, 30 June 2008 (UTC)
thread_title:  Artist's impression? 

message: Noting this edit, are we sure that the dimensions are now correct? W/m^2/Hz isn't total flux but it could well be correct, and I don't have the source available to me right away. -Stlemur (talk) 16:34, 26 June 2008 (UTC)
thread_title:  Flux 

message: I just asked for a semi-protect, as there have been 9 instances of identical redirect (as of 18:27) but by different IPs.  I am not sure if this is appropriate, as there has been lots of IP interest from other IPs today due to front-page location.  (Congratulations to RJHall!)  Wwheaton (talk) 18:50, 26 June 2008 (UTC)
replies: text: Request declined due to front page status, but I see CluBot handles this pretty well. Wwheaton (talk) 19:21, 26 June 2008 (UTC)
thread_title: [[HAGGAR?]] vandalism from multiple IPs

message: Hello - great article, but I can't find anywhere that makes it clear if this is a galactic or extra galactic object.  While it gives the distance, this wouldn't mean much to most people. 
PhilCC (talk) 19:15, 26 June 2008 (UTC)
replies: text: It's only 6,000 ly distant; well within the Milky Way. By comparison, the nearby LMC is 160,000 ly distant.—RJH (talk) 20:05, 27 June 2008 (UTC)
replies: text: I tried to answer this question, but I'm a little dissatisfied.  I have a poor source that says it's in the Sagittarius Arm, and a good one that shows it along the Orion Spur but does not say that it's actually in it.  The galactic coordinates I found, according to the new artwork for the Milky Way with two main arms, seem to point to it being firmly in our little Orion Spur.  I don't really know the good ways to search astronomical literature and have been using web searches, so no doubt an expert will surpass me here - I should learn how to do this properly. Wnt (talk) 15:07, 29 June 2008 (UTC)
replies: text: I'm not sure I understand why the location in the galaxy is really of significance. Is the idea to pinpoint the location of every Milky Way object to a particular arm or spur? If so, what is the purpose? Thanks.—RJH (talk) 15:33, 29 June 2008 (UTC)
replies: text: Well, if the article were about a city you'd say what state it's in.  And giving it a location helps to explain why it is a special object of study, and helps distinguish it from  the sort of black hole you find at the center of a galaxy. Wnt (talk) 16:12, 29 June 2008 (UTC)
replies: text: Would you tell the reader that a city is on the planet Earth? I don't think that is really necessary. In any event, this article is not about black holes in general; that subject is covered great detail elsewhere.—RJH (talk) 15:01, 30 June 2008 (UTC)
replies: text: Well, I'd tell the reader a city was on Earth if it could be somewhere else!  I honestly believe, at least in the U.S., that the average reader has absolutely no idea whether this black hole is any nearer or further from the Earth than a quasar.  I think that specifying that the hole is somewhere pretty close to our own little neighborhood of the Milky Way helps to drive home the idea that the Earth swirls around with some pretty strange things.  But really, my underlying motivation is that visualizing a topic of study as a place with objects in particular locations is a well-known mnemonic device.  As the structure of the Milky Way and positions of objects within it become more clearly established, learning objects as members of specific arms and spurs will be a handy way to keep track of what well-known objects are here, how far they are from the center (and thus how metal rich, for example, thought that doesn't apply to this particular case!). Wnt (talk) 11:23, 5 July 2008 (UTC)
replies: text: Well, you'd tell somebody the location of a city on Earth because it is navigable. The same can not be said of Cygnus X-1. To give the location of a celestial on a particular spiral arm is only useful if the arm has a specific relevance to the subject. This article is not about the Milky Way or the structure of our galaxy, so the detail is way off topic.—RJH (talk) 16:18, 6 July 2008 (UTC)

text: I have changed the first sentence of the lead paragraph to delete a redundant "strong" (also in next sentence) and inserted "celebrated galactic" to indicate its iconic status (among us space freaks...) and local nature.  But really, I think no more about its location is required.  The term "galactic" may not mean much to a true novice at first look, but it is made clear from the rest of the article, where the identification with a star system, OB association, and nearby distance (6,000 lt-y, 1/16 the size of the Milky Way) all indicate its status as galactic.  Regions within the Galaxy are not precisely mapped out (eg, astronomers would not say "Cygnus sector", though Captain Kirk may in a few centuries), mainly because distances cannot be precisely measured for objects that are more than a couple of thousand light years away.  This latter limitation is changing rapidly nowadays, and probably in a century we will have a radically improved map of the 3D structure of the Galaxy. Wwheaton (talk) 20:18, 5 July 2008 (UTC)
replies: text: In my opinion, it would not hurt to have a top-down image of the milky way and mark the locations of this and our solar system.  Obviously the image would not be precise, since we can only draw artistic approximations, but it would help the ordinary person (such as myself) understand roughly the location of this object in relation to ourself and the surrounding galaxy.  This is really no different than why you would draw a image of our solar system for an article on Mars.  You can't actually navigate there, but it helps people to understand what is meant by orbit information to see a picture approximating it. Ddcorkum (talk) 06:01, 19 December 2009 (UTC)
replies: text:  I'm sure you're right. However, the map maker would need to be careful not to be accused of WP:OR.—RJH (talk) 21:43, 19 December 2009 (UTC)
thread_title: LOCATION

message: Why is this "celebrated"? In what way and by whom? According to the MW dictionary, the word means "known and praised widely," so who praises this astronomical object? -Miskaton (talk) 20:39, 11 August 2008 (UTC)
replies: text: It used to say "strong", but that is a little vague. I'm assuming celebrated was chosen as it is synonymous with famous.—RJH (talk) 22:33, 11 August 2008 (UTC)
replies: text:  I changed it to well known. celebrated was a little strange. 189.104.118.146 (talk) 22:50, 11 August 2008 (UTC)
thread_title:  "celebrated"? 

message: The following article discusses the slow rotation of Cyg X-1 and the implications for its formation. (I'm assuming they mean the rotation rate of the black hole, although it's somewhat ambiguous.)
:
I checked the listed references but I couldn't find the information about the rotation rate and supernova implications. (Probably I'm just missing it or not interpreting it properly.)—RJH (talk) 17:41, 1 September 2009 (UTC)
replies: text: I think (just from reading the abstract of the ApJ article) that this may refer to the rotation speed of the supergiant HDE 226868, not the BH companion.  It seems that they are modeling the stellar wind flow near the star.  I do not have access to the full text from this computer, however, so I cannot be certain. Wwheaton (talk) 18:42, 2 September 2009 (UTC)
replies: text:  I guess I missed it the first time through, but the last sentence refers to the rotation rate of the black hole. Sorry, my goof.—RJH (talk) 19:51, 3 September 2009 (UTC)
replies: text: I'm not sure you goofed, it isn't really clear from the abstract.  I am actually in doubt about how one defines the rotation rate of a BH, since it has no surface.  Possibly the "circumference of the event horizon" (? defined how?) divided by c, but this is beyond my knowledge.  If I have time (unlikely) I'll try to do a bit more investigating. Yours in ignorance, Wwheaton (talk) 00:01, 4 September 2009 (UTC)
replies: text:  Maybe they're somehow measuring the rate of frame dragging?—RJH (talk) 18:58, 4 September 2009 (UTC)
thread_title:  Rotation 

message: The following 2009 source has some updated values for the primary:
:
It sounds like many of these parameters are still fairly uncertain. Should we go with these updates for the infobox, or stick with the current numbers and wait until they are further refined? Thank you.—RJH (talk) 21:53, 26 July 2010 (UTC)
thread_title:  Article updates 

message: The article states that "the no hair theorem guarantees that black holes do not have magnetic poles".  However, the no hair theorem actually says that black holes are completely specified by mass, charge, and angular momentum.  If the black hole has charge and angular momentum, that defines a magnetic pole--it's enough to write the entire Faraday tensor, which includes both electric and magnetic fields.Mpalenik (talk) 22:25, 9 January 2017 (UTC)
thread_title:  No hair theorem 

message: Hello fellow Wikipedians,
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thread_title:  External links modified 

message: Tonight's NOVA episode showed Kip Thorne holding and talking about the original document for his bet with Hawking, which he said was made in 1974. The document was handwritten by Thorne, signed by both men, stamped with both British and US postage, and finally bears Hawking's later fingerprint with the words "Conceded Stephen Hawking June 1990." The witness statement at the bottom of the document--which could only have been added at or after the time the bet was made--states "Witnessed this tenth day of December 1974". The witness signatures include one that is completely illegible, one that reads approximately "Anna Zythar", and one that is almost certainly Werner Israel's.
A low-quality scan of the same document can be seen online at http://www.star.le.ac.uk/~sav2/blackholes/xrays/Hawking_Thorne_wager.jpg .
So I'm inclined to change the year of the bet in this article and in the Thorne–Hawking–Preskill bet article (where I've also posted a note like this on the talk page) in spite of the fact that Hawking, much later, clearly said "we made the bet in 1975." Any objections? 98.247.224.9 (talk) 06:46, 11 January 2018 (UTC)
thread_title:  1974, not 1975 

message: The infobox seems to be a confusing mixture of information about the X-ray source and information about the star.  The magnitude given is that of the star, the mass is the X-ray source, and so on.  I can't even figure out which object some of the data pertains to.  There are two separate objects, so perhaps there should be two separate infoboxes. 2601:C6:4100:F980:C0E3:A7E3:4822:8573 (talk) 17:16, 23 October 2020 (UTC)
thread_title:  Infobox confusion 

message: Miller-Jones et al. (2021) give a larger distance measurement of  thus a greater black hole mass of : 
"Cygnus X-1 contains a 21–solar mass black hole—Implications for massive star winds" Nrco0e (talk · contribs) 19:36, 19 February 2021 (UTC)
thread_title:  New mass measurement 

message: Hey. I'm in the process of translating this page for the Hebrew Wikipedia as part of a university course, and I'm going over some sources regarding the Astrometry of Cygnus X-1. This page cites the proper motion values as 
RA: −3.37[1] mas/yr
Dec.: −7.15[1] mas/yr
With both values seemingly coming from source [1], "Validation of the new Hipparcos reduction- Floor van Leeuwen". Now, I looked over this source and couldn't find any data regarding the proper motion values (or anything else, for that matter) for Cygnus X-1 under any of its aliases. I might be reading the data wrong- It should be noted that I'm no expert in astronomy, just an amateur- But a simple attempt at matching numbers and names results in no matches.
There's also source [2], which claims different values for the proper motion, at -3.882 -6.171 [0.048 0.054 90] mas/yr. This discrepancy, in my view, is problematic.
What do you think? Should the info and sources in this page be changed? OmerDavidSegal (talk) 11:59, 1 April 2021 (UTC)
thread_title:  Astrometry data and sources [1],[2]