Talk:Sagittarius A*/Archive 1

Sgr A* vs. Sgr A
The "A*" is probably a matter of notation. The bright stuff at the center has been called "Sagittarius A" for quite some time, and once resolution improved they discovered it had two parts, a hypernova remnant and something else I forget--these are "Sagittarius A East" and "West." Further improved resolution came up with a superpowerful radio point--and, with a point nestled within Sagittarius A, it wouldn't be too much of a stretch to assign it a "*" to indicate this.

This is just conjecture; I'm not an astronomer. --The Centipede — Preceding unsigned comment added by 165.134.186.199 (talk • contribs) 01:24, 13 April 2005 (UTC)


 * I've reverted the changes, and cleaned up the text to make the distinction between Sagittarius A and Sagittarius A* clearer. This article should probably actually be merged with/redirected to the Sagittarius A article, as there isn't much extra information presented here. --Christopher Thomas 02:00, 13 Apr 2005 (UTC)

What's a supermassive blackhole eruption like?
Is this object going to erupt in 10 million years? Xaxafrad 05:51, 11 December 2006 (UTC)
 * Nope. Deleted the nonsense. --IanOsgood 02:20, 13 December 2006 (UTC)

I'd love you to try to justify this statement.
''Later observations determined the mass of the object to be about 3.7 million solar masses within a volume with radius no larger than 6.25 light-hours (45 AU) or about 4.2 billion miles. For comparison, Pluto orbits our Sun at a distance of 5.51 light-hours or 3.7 billion miles.''

''This is compatible with, and strong evidence in support of, the hypothesis that Sagittarius A* is associated with a supermassive black hole. While it is possible for the observed mass within the observed volume limit to be distributed among multiple objects, any such objects would undergo orbital collapse into a single black hole anyway within a few hundred years at most, a negligible amount of time compared with the lifetime of the galaxy.''

45 AU is 180 times more radius than is necessary for 3.7 million solar masses to not need to be a black hole. It doesn't matter if it's one body or many. That is enough space so that it could be any number of stable systems which aren't black holes, and which need never become a black hole. The last sentence of this passage is wrong for many reasons. --76.224.88.42 (talk) 18:07, 20 December 2007 (UTC)


 * You know I thought the same thing when I read this article. I cannot speak for whoever edited this.  However, the general concept is SrgA* is a cluster of bosons, a black hole cluster that's going to be a super-massive black hole in about 100 years, or a super-massive black hole.  As you may or may not know, super-massive black holes have accretion disks (like our sun?), and it is the X-rays reflected and refracted of the accretion disk that we detect. Note that one is able to figure out the maximum size of really bigs objects due to its angular momentum L, speed of light, and the objects mass. The maximum possible size of the INNER radius of this accretion disk is limited by the black hole's aforementioned spin and two other solutions.  I believe these formulas might be the Schwarzschild solution and the Kerr-Newman solution, but I know for sure is that they must be exact solutions in general relativity. Anyways with these to solutions, it turns out that the inner radius is between 6GM/c^2 to GM/c^2 in size depending on the mass of the object. Since the black hole has to fit within this disk, it cannot be bigger than the inner radius. --128.61.72.86 (talk) 21:27, 21 February 2008 (UTC)
 * Also, I DO realize that there are I alot of holes the explination I gave; therefore, I would like to direct you to someone who can give you to a better explanation http://www.physics.arizona.edu/%7Edrb/ David R. Ballantyne]. He is actually the guy whose lecture Note, that his e-mail link is anti-spam (text). I still am not sure how they got 45 AU. Shouldn't it be around 6 times the orbital radius of Mercury? --128.61.72.86 (talk) 21:27, 21 February 2008 (UTC)


 * This isn't quite a scientifical text, but since they have completely different figures from those given here I think it'd be worth to check: ec.europa.eu/research/.. --84.56.201.227 (talk) 01:16, 6 March 2008 (UTC)

Biased Attribution
The first paragraph implies that only in 2002 was it discovered this source is a compact object (ie a black hole). In fact, work has been going on for decades toward this end, this includes work of Genzel, Ghez and other researchers. Sgr A* is in every astronomy textbook as a black hole. As written, the article wrongly attributes full credit for discovery of the black hole to one researcher, and was likely written to promote that researcher's work. Attribution should be secondary to a good description of the object itself. If this is not fleshed out better to include previous research, I will remove the specific attribution, and just say "astronomers have determined" etc. Substar (talk) 15:49, 14 April 2008 (UTC)Substar

Distinction between central black hole and Sagittarius A*
I'm confused. The article for this, and the article for the Galactic Center, both seem to make a distinction between Sagittarius A* and the supermassive black hole at the center of the Milky Way. The way it seems, "Sagittarius A*" is more of a name for the general area, or for the radio and x-ray emmissions of the accretion belt of the black hole, and the reason for the distinction is that we haven't seen the black hole itself.

Why is there the distinction? I always thought of "Sagittarius A*" as the name of the black hole itself. If Sagittarius A* doesn't stand for the black hole, then does the black hole have any sort of name? Should the central black hole have it's own article or anything? I'm just curious. Shnakepup (talk) 16:31, 26 June 2008 (UTC)


 * Sgr A* is the observable, compact (unresolved) radio source. The recent Nature article (Nature 455, p.78-80, 2008) provides some evidence that Sgr A* is smaller than the expected apparent diameter of the event horizon of the black hole. This indicates that Sgr A* is not centered on the black hole, but may be a feature in the innermost region of the accretion flow (there's supposed to be a gaseous disk orbiting the hole, with matter accreting onto the hole from the innermost edge of the disk.. it could e.g. be an orbiting 'hot spot' in the disk). 134.100.120.105 (talk) 11:34, 2 October 2008 (UTC)

Map?
I like to look up into the sky and recognise stories, myths and cosmologies that the heavens provide. It would be nice if someone provided a constellation map of the Sagittarius that showed which visible stars that approximates the centre of our galaxy. —Preceding unsigned comment added by Xact (talk • contribs) 01:31, 23 January 2008 (UTC)

It's pretty much where the steam would be leaving the spout of the teapot. Look on the net for photos of Sagittarius against the Milky Way. The brightest spot near the spout is the centre of the galaxy - and thats where Sgr A* is. —Preceding unsigned comment added by 61.68.176.2 (talk) 11:12, 8 December 2008 (UTC)
 * For example... --IanOsgood (talk) 22:06, 8 December 2008 (UTC)

Age?
Even if it's not a supermassive black hole, has anyone approximated the age of Sagittarius A*? --Yoshiaki Abe (talk) 04:24, 1 September 2008 (UTC)


 * No-one has made any particular claim about its age, as far as I know. But it seems that the black holes formed very early in the universe, and then co-evolved with the material around them: the black holes grew, and the material formed into galaxies. So Sgr A* is about as old as the universe itself, but would've been much much smaller at first.Warrickball (talk) 11:07, 25 December 2008 (UTC)

Event Horizon imaging?
The article cites a VLBI image "the edge of the event horizon". I have been unable to locate any source for such a claim. I do not argue the veracity, I merely wish more detailed information, and hope the source will provide it. I would deeply appreciate any direction.Azutjw (talk) 20:37, 11 November 2008 (UTC)


 * Well, the article refers to Chris Reynolds article in Nature, which itself refers to a paper therein. I've read both, and there has been some misunderstanding by whoever added to the Wiki article that there's a VLBI image of the event horizon.


 * The measurements in the paper (Reynolds' article is more of a comment/analysis) has an angular resolution smaller than the GR-predicted size of the central BH's event horizon, but they still detect a source consistent with a central point. So either Einstein is wrong (which is seldom a good position to take) or Sgr A* is actually slightly off centre from the central black hole. The paper gives reasons for this, but there is certainly no claim that the event horizon has been imaged.


 * I'll clean up that section of the article a bit now to reflect the reality of the observations.
 * Warrickball (talk) 11:07, 25 December 2008 (UTC)

The same findings were published in the September 27 issue of Science News (http://www.sciencenews.org/view/generic/id/36161/title/Milky_Ways_black_hole_seen_in_new_detail), where they clearly state Sagitarrius A* is located off-center from the supermassive black hole. Given this information, I believe sections of this article referring to the theory that Sagitarrius A* is the black hole at the center of our galaxy should be removed to reflect the realities of the latest research. - King's English —Preceding unsigned comment added by Kings english (talk • contribs) 15:33, 27 April 2009 (UTC)
 * From my understanding, the image of the black hole in this article is not from Sagittarius A, rather, a photo from a single telescope that was used to construct the final black hole image of the supermassive black hole in Messier 87. This image really needs a source, or be taken out, but if you go to the original live stream of the unveiling, I believe this is one of the photos that they presented, again, not of Sagittarius A, but of Messier 87's black hole.

There is no evidence to support that it "must be a black hole beyond any reasonable doubt"

 * Reinhard Genzel, team leader of the research said the study has delivered "what is now considered to be the best empirical evidence that super-massive black holes do really exist. The stellar orbits in the galactic centre show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt."

There is no evidence proving that it is a black hole. There is only evidence that it is a supermassive object somewhere nearby but it's size is not known. Also it's mass is only deduced based on movements of other objects and we all know interpretation of such movements is far from straightforward as results contradict general relativity unless speculative dark matter is introduced. All this means that we don't know what it is, it may be a black hole (if they can even exist, singularities are a very strong argument against their existence, especially since cosmic censorship hypothesis has been disproved) or it may be some other exotic object, it may be an object whose nature we are not able to understand yet. We still don't have a theory combining quantum mechanics and general relativity, such a theory once discovered may significantly alter our understanding of cosmology. In any case there is no evidence to support the claim that central mass of Sagittarius A* "must be a black hole, beyond any reasonable doubt" only that it must be a supermassive object and it's certainly not the same thing.Sergiacid (talk) 04:50, 19 May 2009 (UTC)

Mass
This article seems to have fallen victim to one of the more annoying mistakes that can be found on Wikipedia: quoting a source that supposedly buttresses the stated fact, but which in fact does not. I am speaking of how the mass of Sagittarius A* prime has a mass of 3.7 million suns. In fact, both reference #5 and #7 say it is 4.1 million suns. Specifically, Ref. #5, The First Measurement Of Spectral Lines In A Short-Period Star Bound To The Galaxy’s Central Black Hole: A Paradox Of Youth states that its mass is 4.07 ±0.62 million, which they roughed to 4.1 ±0.6 million in the abstract of the paper. Further, Ref. #7, UCLA Galactic Center Group, also says it is 4.1 million solar masses.

I’ve corrected the article accordingly. Greg L (talk) 05:58, 21 May 2009 (UTC)


 * In this case, the existing reference was updated in the background due to better measurements (a fact of life as science advances). Thanks for updating the article. --IanOsgood (talk) 19:12, 21 May 2009 (UTC)


 * I spent more time looking through the article. Down at the bottom is superior 16-year-long measurement with an uncertainty that is an full order of magnitude better, at 4.31 ±0.06 million solar masses: Monitoring stellar orbits around the Massive Black Hole in the Galactic Center by S. Gillessen et al. I updated the value up at the top, near the lead and doubled up on that citation. Greg L (talk) 06:13, 22 May 2009 (UTC)

Solar mass
Now, the BBC series "Horizon" (broadcast November 3rd, 2009) discusses Black Holes, and also notes that Sagittarius A* is (circa) 4.31 million times heavier than the Sun. Basing on this, I have put an approximate median for the Black Hole as:

8,573,021,000,000,000,000,000,000,000,000,000,000,000,000kg

or... 8,573,02136

I calculated this by multiplying 1,989,100,000,000,000,000,000,000,000,000kg (The mass of the sun) by 4,310,000,000.

-- OsirisV (talk) 23:30, 3 November 2009 (UTC)
 * You mean " 8,573,021 &times; 1036 kg ", which is too big by a factor of a million (it should be 8.57 &times; 1036 kg). Anyway, it's more comprehensible if the mass is expressed in solar masses.  Writing it in kilograms is rather like weighing yourself and expressing the result in amu. Spacepotato (talk) 23:05, 5 November 2009 (UTC)

More detail on observations
I added some info from the cited papers about how the observations of S2 (and nearby stars) were made with NIR interferometry. The fact that such observations could be made at all, given the enormous density of stars, gas and dust along the line-of-sight from Earth to the galactic centre is really astounding to me. If anyone is knowledgeable enough to expand on this, in my POV it would be informative to explain just how technically challenging these observations are. Also, I got the impression from the refs that measuring the distance to the galactic centre very accurately, which was also accomplished by these observations, is important in astronomy for the calibration of distance scales, so I added this. Puzl bustr (talk) 21:05, 8 December 2009 (UTC)

Proposed merge with Sagittarius A
Why exactly is the merge being proposed? I'm not saying that it would be a _bad_ thing, I just don't see what's wrong with the current situation.

If a substantial number of lurkers come forward in favour of the merge, I'll be happy to merge it, but I'd prefer not to bother. --Christopher Thomas 05:10, 27 March 2006 (UTC)

Nay.
I came to this article look specifically for information on Sagittarius A*. Merging would be confusing and all together pointless Nintenfreak 21:51, 30 March 2006 (UTC)
 * Agree. They are two different things that have very similar names for historic reasons. Sagittarius A is the central region of our galaxy. Sagittarius A* is the much smaller, detectable shell around the super-massive black hole at its heart. It's like saying we should combine the sun and solar system articles. agr 22:10, 30 March 2006

Nay2
No merge... above arguments say it all. Sagittarius A* is the ultimate hub of our galaxy, and is deserving of a wikipedia survey peg. NevilleDNZ 09:40, 4 April 2006 (UTC)

I say Nay
No merge, A* is a more specific feature Zzzzzzzzzzz 00:13, 13 April 2006 (UTC)

Nay
I also believe that the two articles shouldn't be merged, because Sagittarius A simply refers to the area (and objects within it) where the radio emissions that were detected by the Bell Telephone Laboratories (as shown here) are coming from. Because the objects are so critically different there would be a large amount of confusion between the two. — Preceding unsigned comment added by Smulumudi (talk • contribs) 00:18, 9 June 2011 (UTC)

I've removed the merge templates, as we've had 3 votes against and one abstention since the merge was proposed. --Christopher Thomas 18:43, 14 April 2006 (UTC)

Event horizon radius
Anyone know the radius of the event horizon of such a black hole? Just wondering how close S2 (star) comes. --Doradus (talk) 15:47, 4 April 2008 (UTC)


 * Well, the event horizon of a non-rotating black hole is 2GM/c². A good approximation for that is 3 km per solar mass. So Sgr A*'s event horizon would have a radius of about $$3.7\times10^6\times3\mathrm{ km}\approx11\times10^6\mathrm{ km}$$. Warrickball (talk) 11:07, 25 December 2008 (UTC)


 * New data (from Nature article, 12/2011, see reference below in "dustcloud" section); this is in the text (not abstract) of the article, so available online only to subscribers. They say the dustcloud will pass by the supermassive black hole at a  "...pericentre radius [of] a mere 36 light hours (3,100 Schwarzschild radii)", implying that the Schwarzschild radius of the supermassive black hole (if that's what it really is) at the center of the Milky Way would be 36 light hours / 3100 = ~0.012 light hours = ~12.5 million km.  This number is similar to, but slightly improved from, Warrickball's number (11 million km) above.  (In a non-rotating black hole, the Schwarzschild radius and the event horizon radius are the same, I believe).  Could somebody edit the main article to reflect this?  - lanephil Lanephil (talk) 22:12, 20 December 2011 (UTC)

Problem with x-axis scale in "Galactic centre orbits.svg" graphic?
I just noticed a possible problem with this graphic - which is otherwise great, and many thanks to wikipedian Cmglee for making it. (Full disclosure, I certainly ain't no astronomer :-) so forgive me if I screw this up.).

I think the x-axis scale (Right Ascension, in hours, minutes, and seconds, with the darker scalelines 0.1 seconds and the smallest division 0.02 seconds) and the y-axis scale (Declination, in degrees, minutes, and seconds, with again the darker scalelines 0.1 seconds and the smallest division 0.02 seconds) may be messed up. Having looked up Right Ascension and Declination in (of course) wikipedia, it turns out that Declination is normally scaled in arcseconds (360 degrees in a circle, each divided into 60 arcminutes, each divided into 60 arcseconds - so 360x60x60=1,296,000 arcseconds in a full circle). However, Right Ascension is *not* scaled in arcseconds; instead it is in "seconds of Right Ascension", and 1 second of Right Ascension is actually 15 arcseconds. (From Wikipedia on Right Ascension: "a second of right ascension equal to 15 seconds of arc."). Actually, this makes sense; for Right Ascension, there are 24 hours, each divided into 60 minutes of Right Ascension, each divided into 60 seconds of Right Ascension, so:  24x60x60 = 86,400 seconds of Right Ascension in a full circle. But since 1 second of Right Ascension = 15 arcseconds, then 86,400 x 15 = 1,296,000 arcseconds in a full circle, ok, it all fits. So the graphic x-axis scale is distorted? I see two options:

(a) the y-axis, Declination, is in tenths and hundredths arcseconds, but the x-axis, Right Ascension, is in tenths and hundredths of seconds of Right Ascension, units which are 15-fold bigger. Or, alternatively,

(b) both scales are in arcseconds, and the X-axis is improperly labelled. Arrrrgh.

My guess is (b). This all stems from the confusion that you (or me, a definite amateur) would think a "second" would only have one meaning when working in the equatorial coordinate system on the celestial sphere, but really it has two meanings. Bad choice of terminology, darn those astronomers, but it's no doubt too late to change. Better to discuss Declination in "seconds of arc" or "arcseconds", but Right Ascension in "seconds of Right Ascension", where 1 second of Right Ascension equals 15 arcseconds. Sheesh. So, anyway, I think the graphic needs fixing, but I'm not brave enough to try it myself. I hope Cmglee or somebody can address this. My guess is that the x-axis should be relabelled, and I suspect it should really be "Right Ascension difference (in arcseconds) from RA 17h 45m 40.045s (note, 15 arcseconds = 1 second of Right Ascension)". Similarly, the y-axis might be relabelled "Declination difference (in arcseconds) from Decl -29 deg 0' 27.9"  "  Also, the long-form caption as it appears in the < File:Galactic centre orbits.svg  > page (but not in the main Sagittarius A* article) should also be fixed, assuming I've got all this straight, so as to make the scale on both axes in arcseconds more clear.

By the way, it was *brilliant* to put the small Solar System / Sedna / Eris / Neptune / Pluto down there in the lower righthand corner for scale comparison. To further improve it, perhaps the short form caption in the main page (and the long form caption in the < File:Galactic centre orbits.svg > page should be amended to include something like: "In the small Solar System scaling graphic at the lower right, Pluto's orbit is the smallest near-circle, about 30-49 AU, and the long, very off-center ellipse is Sedna's orbit, with aphelion 937 AU and perihelion 76 AU."

Also, in the long form caption, there is "the scale is assumed to be 7940 AU/arcsecond"; the new Nature paper (see "dustcloud" below) has an improved number, based on a revised distance of 8.33 kpc to Sagittarius A*, and now it should probably be 1 arcsecond = 40 mpc = 1.25 × 10e17 cm = 8,251 AU;  other stuff there would also need to be fixed accordingly. Also in that long form caption, it would be clearer to say that the separation between bold lines (0.1 arcseconds) represent about 825 AU. Let me know if this all makes any sense. Thanks. - lanephil Lanephil (talk) 20:21, 20 December 2011 (UTC)


 * Lanephil has rightly observed that the axis labels are misleading at best. I had initially distinguished them using s and " but thought it makes more sense if both scales were the same. The graph was redrawn from this paper, in which the author used the unit arcsecond. As " is a common abbreviation for arcsecond, I used it to fit the ticks. What do other editors/readers here think?


 * I haven't come across said Nature paper, so if anyone could spare some time, please amend the description, caption and/or image to the latest sources. Ditto for the comparison Solar System. Thanks, cm&#610;&#671;ee'&#964;a&#671;&#954;'ma&#953;&#671; 18:26, 23 December 2011 (UTC)

Something to add - dustcloud to impact Sagittarius A* in 2013
Today in the New York Times it is reported that a dust cloud is headed to impact (or else come really close to) the presumed black hole at the center of Sagittarius A*, with impact (or close approach) to be visible to Earth-based telescopes (infrared telescopes on the ground and in orbit, and X-ray telescopes in orbit) in 2013. See < http://www.nytimes.com/2011/12/20/science/forecast-for-sagittarius-a-black-hole-a-cold-gas-cloud.html?ref=todayspaper  >. See also "A gas cloud on its way towards the supermassive black hole at the Galactic Centre", S. Gillessen et al, Nature, doi:10.1038/nature10652, published online 14 December 2011 [actual hardcopy publication date, volume, page number TBD; < http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10652.html > ]. Could somebody insert a section stating this? It'll be VERY cool to see the pics and videos that come out of that. Thanks. - lanephil Lanephil (talk) 20:32, 20 December 2011 (UTC)


 * a HA, just noticed, there's a great ESO video on this dustcloud, but not linked to this page; instead it's in the < Supermassive black hole > page, at < http://en.wikipedia.org/wiki/File:A_Black_Hole%E2%80%99s_Dinner_is_Fast_Approaching_-_Part_2.ogv >;  the original is at < http://www.eso.org/public/videos/eso1151b/ >.  That link should probably be added to this article, if anybody's in an editing mood.  cheers.  Lanephil (talk) 03:23, 25 December 2011 (UTC)

Tidal Forces?
Article currently has "The radius of the central object must be significantly less than 17 light hours, because otherwise, S2 would either collide with it or be ripped apart by tidal forces". But the radius of a body of a particular mass does not classically affect the tidal field at a particular greater distance - can things be much different here? 94.30.84.71 (talk) 15:55, 27 June 2012 (UTC)

Gas Cloud Passing?
I have read that a gas cloud will pass near Sgr A* in mid-2013 (ERT), and be significantly disrupted. If true, that seems worth mentioning. 94.30.84.71 (talk) 15:58, 27 June 2012 (UTC)

Update mass
The page Supermassive black hole seems to be based on newer research and mentions a mass of 3.6 millions times the mass of the Sun. See also the UCLA article linked from there. --Andrei Badea 10:19, 17 April 2006 (UTC)


 * New data (from Nature article, 12/2011, see reference below in "dustcloud" section). This is buried in the NATURE supplementary info, available online only, to subscribers only I think.  They say the supermassive black hole at the center of the Milky Way has a mass of 4.31 × 10e6 solar masses, i.e. 4.31 million solar masses.  This fits with how the article currently reads.  Cool.  Lanephil (talk) 22:12, 20 December 2011 (UTC)

i have also a problem with this: "The radius of the central object must be significantly less than 17 light hours, because otherwise, S2 would either collide with it or be ripped apart by tidal forces. In fact, recent observations[16] indicate that the radius is no more than 6.25 light-hours, about the diameter of Uranus' orbit, leading to density limit 8.55×10^36 kg / 1.288×10^39 m^3 = 0.0066 kg/m^3"

now, compare that 0.0066 kg/m^3 with earth calculated density 5.515 g/cm^3 ... wow! ordinary earth matter density many times more that a black hole!? we live on a superdense black hole already?Totedati (talk) 08:34, 16 July 2012 (UTC)


 * Not a problem. The mass itself is in the form of a singularity of infinite density. The radius mentioned is that of the event horizon. The average density within this large volume can be surprisingly small; that of water was once given. --IanOsgood (talk) 04:23, 17 July 2012 (UTC)


 * formally true buttttt ... what if is NOT an infinite singularity ( real volume → 0 and density ← ∞ )!? ... we can apply here a common sense logic! because the infinite is forbidden to heavenly spheres of a surreal god, for us, mere mortals, what we have is a real thing which is quantifiable and measurable only by this puffy even horizon radius! only that thing is real, plus many time more gravitational pull! which, i see, can bring to us, using an unhealthy form of logic, the strange conclusion that even if a black hole density is lower that earth density still must be infinitely dense because this is what our equations told us! (LE: which can't be true for any real measurement! we can't measure 0 and ∞! real trajectories of real clumps of matter around that black hole is newer 0 or ∞! no matter how small or big or dense or strange is the measured trajectories!) ... so, why not other way around? an equally sane conclusion can be that between gravitational force field and mass density is an inverse relation! not mass causing the gravitational pull, but the independent gravitational field being the trigger of measurable mass effects sensed by our scientific instruments as clumps of matter! ... this way will be no more a need for strange physical objects like black hole singularities with infinite mass density and infinitesimal spatial volume! Totedati (talk) 00:52, 20 August 2012 (UTC)

Shortest-period orbit
A new star with an even shorter orbit than S0-2: S0-102. 46.126.76.193 (talk) 21:06, 6 October 2012 (UTC)

Yeah! cm&#610;&#671;ee'&#964;a&#671;&#954;, save us! Please add S0-102 to your awesomely pretty chart! Zirconscot (talk) 13:28, 7 October 2012 (UTC)

"The only known type of object which can contain 4.1 million solar masses in a volume that small is a black hole." sentence is very wrong
"A typical neutron star has a mass between 1.35 and about 2.0 solar masses [1][2], with a corresponding radius of about 12 km" from Neutron star. So 4.1 million solar mass of neutron star density would have about 20000km radius, or 1/7 light second of diameter - its 100000 smaller than limit from this articles, like 6.25 light hours ... ? — Preceding unsigned comment added by 89.78.183.53 (talk) 18:50, 17 October 2011 (UTC)
 * No, if a neutron star is too massive, quantum degeneracy pressure can no longer support it and it collapses into a black hole. See Tolman–Oppenheimer–Volkoff limit. The largest observed neutron star is about 2 solar masses. --IanOsgood (talk) 19:47, 17 October 2011 (UTC)
 * But presented reasoning doesn't prove that it's a black hole - it is based on density limit, while there are many known objects of much larger density (neutron star has 10^15 times larger). The limit you are referring to is about physics we don't really understand - are there any experimental evidence about such state of matter? Until they improve radius limit 100000 times, there in fact still remain a possibility that it's just a very large neutron star, untrue? Wrong is also 'known type of object' - if Sagittraius A* is the only really proven to be a black hole, it looks like proving by assuming the thesis - the existence of black holes. 89.78.183.53 (talk) —Preceding undated comment added 20:15, 17 October 2011 (UTC).
 * The issue here is less that we don't understand this, than that *you* don't understand it. You put a large emphasis on density here, but density is not all that relevant for a black hole in the sense that there isn't some constant critical density that results in a black hole. Instead, average density a region can have before it collapses to a black hole decreases with its radius. For example, a glass of water does not collapse into a black hole, but if you had a ball of water 85 AU in radius (with the same density as normal water), it would collapse. Amaurea (talk) 11:42, 25 August 2013 (UTC)
 * If it is not wrong, it is at least misleading - for objectivity there should be at least clearly stated density limit for 4.1 millions of solar masses and 6.2 light hours radius (200 smaller than of earth atmosphere) 89.78.183.53 (talk) 07:12, 19 October 2011 (UTC)

A LOT of problems with this article and this talk page. First as far as I know (not that much, I admit) a black hole is the region around a gravitationally collapsing singularity bordered by its event horizon. Not necesaarily including its ergosphere. Second, it is an assumption that neutron degeenerate matter will collapse into a singularity (upon reaching a certain mass). The discussion about neutrons stars, quark stars, and black holes is highly speculative. SagA* is a REAL world observable, not a theoretical construct, and should be kept logically separate from the speculation (even tho' it is based on our best current science) that it constains a black hole. As far as we know there is nothing to prevent a neutron star from collapsing into a singularity, but until we have a plausible quantum gravitational theory, it is really quite radical to assume there is no other explanation for our observations. Absence of evidence is not evidence of absence. Small, dense, with lensing does not require the conclusion that it is a singularity. The point being there may be additional states of matter beyond neutron/quark densities but less than the infinities of a singularity. Other issues seem secondary. Needs Improvement71.31.149.224 (talk) 23:14, 1 July 2012 (UTC)


 * As of this post, the current version has the mass assertion as "The only widely hypothesized type of object which can contain 4.1 million solar masses in a volume that small is a black hole.", which should be sufficient to keep both the majority (who favor the assumption of a black hole) and the minority (who do not) reasonably satisfied. Braddarb (talk) 13:59, 23 January 2014 (UTC)

New theory - Sagittarius A* may be a worm hole
See https://medium.com/the-physics-arxiv-blog/bb5ae64fa4fa, hat tip http://science.slashdot.org/story/14/05/14/1620225/supermassive-black-hole-at-the-centre-of-galaxy-may-be-wormhole-in-disguise — Preceding unsigned comment added by 151.191.175.205 (talk) 22:05, 14 May 2014 (UTC)
 * Note that anyone can write stories on those two sites under pseudonym. They are essentially blog sites since the articles, in opposite to Wikipedia, can't be edited by anyone. Better source needed please.--BIL (talk) 19:11, 15 May 2014 (UTC)

Why so technical?
Much of what is written in this (and other articles on Wiki) is indecipherable without expert knowledge. What's the point? If people have to take a degree in physics just to read a few paragraphs the article becomes irrelevant except to those already educated in the subject.

I'm not saying remove the techinal detail and jargon but perhaps an encyclopedia should attempt to explain subjects in language accessible to all, not just scientists.

I'm a software engineer, I often have to modify the language I use to avoid the "glazing-over" effect even when talking to people familiar with IT concepts. It takes a little effort but it's worth it to be understood.

Thanks Steve — Preceding unsigned comment added by 2.124.56.236 (talk) 12:04, 22 September 2014 (UTC)


 * Could you please give an example of a paragraph or two that you think are particularly bad? - Parejkoj (talk) 14:31, 22 September 2014 (UTC)

possible error or part that needs clarification
"First noticed as something unusual in images of the centre of our galaxy in 2002,[24] the gas cloud G2, which has a MASS ABOUT 3 TIMES THAT OF THE EARTH, was confirmed to be likely on a course taking it into the accretion zone of Sgr A* in a paper published in Nature in 2012.[25] Predictions of its orbit suggest it will have a closest approach to the black hole (a perinigricon) in mid to late 2013. At this time the gas cloud will be at a distance of just over 3000 times the radius of the event horizon (or ~260 AU, 36 light hours) from the black hole. Opinions differ as to the effect this might have on both G2 and the black hole. G2 appears to already be being disrupted over the past 3 years of observation,[25] and may be completely destroyed by the encounter. If this is the case a significant amount of it may be accreted by Sgr A* which could lead to a significant brightening of X-ray and other emission from the black hole, likely to last over the next several decades. Other astronomers have suggested the gas cloud may be hiding a dim STAR, OR EVEN A STELLAR MASS black hole, which would hold it together against the tidal forces of Sgr A* and the ensemble may pass by without any..."
 * The mass of a dim star or stellar mass black hole would be much more than 3 times that of Earth. If you can fix or clarify this, thanks in advance.Rich (talk) 22:48, 12 January 2013 (UTC)
 * Most likely, the mass of the cloud is not measured directly, but instead inferred from its size and luminosity. If a dim star is hiding in it, then the total mass of the cloud would of course be much greater. Amaurea (talk) 11:49, 25 August 2013 (UTC)


 * new paper suggests a that G2 is the aftermath of of a binary merger
 * http://iopscience.iop.org/2041-8205/796/1/L8/article
 * I can't get past the paywall mind.©Geni (talk) 15:34, 5 November 2014 (UTC)

Question
isn't Sagittarius A* the name of the black hole rather than its location?Huritisho (talk) 08:00, 26 September 2015 (UTC)
 * Sgr A* is the name of the compact radio source, which is thought to be associated with the BH. That's why the article says that Sgr A* is the "location of" the BH. Spacepotato (talk) 22:45, 21 October 2015 (UTC)
 * The black hole is already known to exist. So, is there a name for the BH? Huritisho 22:51, 21 October 2015 (UTC)
 * Although Sgr A* was originally the name of the radio source, people are also using this name to refer to the BH. Apart from that, I don't know of any name for the BH. Spacepotato (talk) 23:11, 21 October 2015 (UTC)
 * Given the designations of the known stars in orbit, the supermassive black hole's designation should probably be Sgr A S0, but as of yet it does not have definite name. Sailorleo (talk) 03:05, 21 December 2015 (UTC)

Parent Star
I'd just like to mention, based on a few calculations... The star that collapsed to form this black hole had a total mass a trillion times the mass of our Sun. Yet, after the supernova, less than one millionth of the mass remained in the black hole, and the rest of the mass, about 10^69 GeV, was thrown out into orbit and formed the Milky Way Galaxy. Clouds of gas and dust cooled and collapsed into new stars and planets, and over billions of years, the black hole took in some of that mass and is now at its current mass, about 10^63 GeV, about a millionth the mass of the galaxy. Let's not forget our galaxy's true parent, the star that died to form this black hole. Zuloo37 (talk) 23:27, 3 December 2014 (UTC)

This is definitely not how the Milky Way was formed...178.15.151.163 (talk) 12:07, 10 February 2016 (UTC)

Supermassive black holes don't form in a single event. ElPeski (talk) 13:09, 25 June 2016 (UTC)

What is the Mass of Sgr A*?
Currently the article provides two contradictory estimates of the mass (4 million solar masses and 1 mil. s.m) while incorrectly claimiing them to be "consistent". Furthermore, the abstract for ftn. 22 actually states about 3.6 M, not 1 M.

Link to abstract of ftn. 22: http://www.aanda.org/articles/aa/abs/2009/28/aa10922-08/aa10922-08.html

Current text below.

Someone who understands astronomy better than me needs to fix this. Yabti (talk) 16:23, 18 January 2016 (UTC)

"The mass of Sagittarius A* has been estimated in two different ways. 1.Two groups—in Germany and the U.S.—monitored the orbits of individual stars very near to the black hole and used Kepler's laws to infer the enclosed mass. The German group found a mass of 4.31 ± 0.38 million solar masses,[2] whereas the American group found 4.1 ± 0.6 million solar masses.[3] Given that this mass is confined inside a 44 million km diameter sphere, this yields a density ten times higher than previous estimates. 2.More recently, measurement of the proper motions of a sample of several thousand stars within approximately one parsec from the black hole, combined with a statistical technique, has yielded both an estimate of the black hole's mass, and also of the distributed mass in this region. The black hole mass was found to be consistent with the values measured from individual orbits; the distributed mass was found to be 1.0 ± 0.5 million solar masses.[22] The latter is believed to be composed of stars and stellar remnants."


 * What you're missing is that the second number, 1.0 ± 0.5, refers to the distributed mass around the black hole, not the black hole itself. Tarl N. (talk) 15:52, 25 June 2016 (UTC)
 * I've copyedited the Sagittarius_A* section and fixed the numbers to match the references cited. I'd appreciate a sanity check. Regards, Tarl N. (talk) 19:13, 26 June 2016 (UTC)

Center of the Milky Way
Would be interesting to indicate the history of the determination of the center of the Milky Way. — Preceding unsigned comment added by Chiloa (talk • contribs) 16:20, 1 June 2017 (UTC)
 * See Milky_Way for details on that determination. Tarl N.  ( discuss ) 23:08, 1 June 2017 (UTC)

Possible intermediate mass black hole near Sgr A*
Science News, original publication. I'm not sure how to include it, but as it is closely connected to the central black hole I think it should get included in the article. --mfb (talk) 20:13, 4 September 2017 (UTC)

Radio Source Sagittarius A*
I was looking at the first paragraph and Wikipedia in general, why is Sagittarius A* always referred to as a radio source first and then further into the article Sagittarius A* is described as a potential black hole? Isn't the evidence at this point overwhelming that it is indeed a black hole? Is this just a case of Wikipedia not being updated yet for the most current information? I've included some good links below that refer to Sagittarius A* as a black hole first a foremost. I originally posted this in the talk section for S-2, but figure it probably will be of more use here.

https://www.nasa.gov/mission_pages/chandra/multimedia/black-hole-SagittariusA.html https://www.britannica.com/topic/Sagittarius-A-black-hole http://chandra.harvard.edu/photo/2015/sgra/ https://news.nationalgeographic.com/2017/04/black-hole-event-horizon-telescope-pictures-genius-science/ https://arxiv.org/pdf/1707.01937

143.165.48.50 (talk) 16:30, 12 March 2018 (UTC)


 * See Section four paragraphs above, where this is discussed. Sgr A* is the radio source; evidence is pretty overwhelming that the compact mass at that location is a multi-million solar mass black hole, but that object has not received a name itself, other than (putative) "Milky Way central black hole". The mass of the object has been measured, and it's dense enough that we don't know what it could be beyond a black hole, but we have not definitively determined that it is a black hole. I recall that we'd have to narrow down the diameter by nearly an order of magnitude to make that determination definitive. Tarl N. ( discuss ) 19:31, 12 March 2018 (UTC)


 * That question was from around 2.5 years ago. Do the above sources hold any weight as to the naming of the object or is that something that can only be done by the IAU? 143.165.48.50 (talk) 13:58, 13 March 2018 (UTC)


 * Did you look at the links I posted? NASA, The Encyclopedia Britannica, National Geographic and a few recent scientific papers all seem to refer to the black hole as Sag A*. Here are two additional links; https://www.e-education.psu.edu/astro801/content/l8_p7.html

https://en.wikipedia.org/wiki/List_of_black_holes (interestingly on Wikipedia's own list of black holes it is named Sagittarius A*) 143.165.48.50 (talk) 14:03, 13 March 2018 (UTC)


 * Sorry my wikipedia formatting is poor 143.165.48.50 (talk) 14:09, 13 March 2018 (UTC)
 * As I said, it's commonly accepted that it's likely the massive object at Sgr A* is a black hole, it has not been proven. People may refer to it as a black hole (because we don't know what it would be if it isn't), but in an encyclopedic article about the object, you can't simply declare it something you haven't shown. In at least one article I read, they made a distinction between the massive object and Sgr A* (as a radio source), indicating they were slightly offset from each other, the radio source probably being in the shell around the dense object. As for Wikipedia's list of black holes, if you look at the text, it basically says "these are things we think might be black holes". Regardless, Wikipedia isn't a reliable source. Tarl N. ( discuss ) 16:28, 13 March 2018 (UTC)
 * By the way, looking more closely at the List of black holes, the putative galactic-massed black holes are not named, instead, the names given (including Sgr A*) are the names of the objects which are believed to contain them. E.g., Messier 31 is the catalog name for the Andromeda Galaxy. Tarl N. ( discuss ) 16:33, 13 March 2018 (UTC)

tension with general relativity
The current version of the article states that "... the radio source of Sagittarius A * is symmetrical.[30] These results are at tension with General Relativity which if no other viable explanation is found within the general relativistic paradigm may demand a new theory of gravitation or modifications to General Relativity itself". However, when checking the scientific article cited, the abstract (and hence the article itself) totally contradicts any tension with General Relativity. In fact, the abstract clearly indicates "We show that multiple disk-dominated models of Sgr A* match our observational constraints, while the two jet-dominated models considered are constrained to small viewing angles". This is, they model the get using General Relativity and find plenty of models. Maybe the sentence about the tension with General Relativity must be deleted. — Preceding unsigned comment added by 2001:F40:902:C02F:7126:81E2:DE37:373B (talk) 18:05, 6 April 2019 (UTC)

Latest observations section has to be updated
Images have been added to the black hole section, but the earlier observations section needs to be updated, as they refer to such observations in the future. I lack the proper knowledge to do a proper fix myself, as it requires more than just a verbe tense change- probably a summary of the papers. --jynus (talk) 20:08, 10 April 2019 (UTC)

The added image is not Sgr A*, but the black hole at the center of M87. See https://iopscience.iop.org/article/10.3847/2041-8213/ab0ec7


 * Indeed it seems like someone added either a simulation of Sag A*, or images of M87 BH to the article, now removed. Probably the commons page should also be edited, if not has been yet to reflect that. A note or comment on the text mentioning the status "images of X were released, but these others are still being processed" may also be useful. --jynus (talk) 20:35, 10 April 2019 (UTC)

Black hole confirmed
On 31 October 2018, a paper was published that confirmed there is a black hole at Sgr A*. Most of the "Central black hole" section states clearly that the existance of the black hole is not certain, but all of those articles are years old. Our knowledge has changed; with new telescopes, new techniques of observation, and direct observation of dust which proves the existence of the black hole. The "Central black hole" section should be revised to remove the outdated statements of uncertainty. I will start my version of this revision in about nine hours because I must go to work now. Nick Beeson (talk) 14:14, 12 November 2018 (UTC)
 * Current status as of this post. I made preliminary edits. I was "bold" in my edits as Wikipedia exhorts editors to be. I tried to keep all still relevent information, while removing all text that suggests it might not be a black hole. I believe that it is clear the most recent paper conclusively puts all doubts to rest. Nick Beeson (talk) 15:32, 12 November 2018 (UTC)
 * Can you point to which paper states definitively that it's a black hole? As best I knew, we believe it's a black hole, but the only thing we know for certain is that it is a gravitationally compact object. Whether that object is actually smaller than the event horizon, as best I know, was not confirmed. Tarl N. ( discuss ) 17:18, 12 November 2018 (UTC)
 * Tarl, I put the references in the article at the end of the paragraph. But here they are. Nick Beeson (talk) 02:09, 11 April 2019 (UTC)

This can't be right?
The article currently says: "In 2016 direct radio images were taken of Sagittarius A* by the Event Horizon Telescope, processed and published on April 10, 2019."

But, those images are of M87*, not Sagittarius A*. I looked at the source cited with this statement, but it makes no mention of images of Sagittarius A*. 82.176.221.176 (talk) —Preceding undated comment added 05:44, 11 April 2019 (UTC)
 * I've amended the wording. According to the already existing source, both were targeted, but only the first has yet been processed, released and papers written about. We will know more about potentual images of Sag A* when (if) released. I also changed the date to 2017, as that was the year for which data was released (probably 2016 was the start of the project in general). --jynus (talk) 06:44, 11 April 2019 (UTC)

The real image from EHT is actually a simulation
At least according to some YouTube comments here: https://www.youtube.com/watch?v=VnsZj9RvhFU&lc=UgzirMx3SeVrODV8Myh4AaABAg ;) --2A02:AA16:3882:3680:7CEF:CC6C:8208:3480 (talk) 20:13, 10 April 2019 (UTC)
 * WP:FRINGE, one presumes. If the best reference is someone talking to a camera and not writing it down, it's not worth the time to even look at. Tarl N. ( discuss ) 21:07, 10 April 2019 (UTC)
 * It's actually a (written) comment from the team that made this simulation. But yeah, not exactly a gold standard information source. Unfortunately, it's the only one I could find at all about this picture. --2A02:AA16:3882:3680:7CEF:CC6C:8208:3480 (talk) 21:49, 10 April 2019 (UTC)
 * We need a WP:RS on that, and it sounds like is claiming to be WP:PRIMARY. Either way, it doesn't apply to Sgr A*, since the image from EHT wasn't of SGR A*. Tarl N. ( discuss ) 01:59, 11 April 2019 (UTC)
 * Ah, I see what's going on. You're referring to an image someone put on there which was mis-labeled and deleted almost immediately. There has been no release of an EHT image of Sgr A*, so any claim of an image from them of Sgr A* was obviously incorrect. Tarl N. ( discuss ) 02:03, 11 April 2019 (UTC)
 * Yes, exactly :) The image is still on Commons, though nominated for deletion: https://commons.wikimedia.org/wiki/File:Sagittarius_A*_black_hole.png --2A02:AA16:3882:3680:7CEF:CC6C:8208:3480 (talk) 09:01, 11 April 2019 (UTC)
 * Many images we see are utterly real portraits of actually objects but are only viewable because of computer processing, e.g. every image in Wikipedia. The image of the black hole is utterly real, but was recorded in radio wavelengths, which are millions of times longer than what the eye can see. Thus the image was computer processed into something we can see. Astronomy has been doing this for 70 years, and only now in the "gotcha" world of the WWW is anyone crying, "Fake, that is a simulation." It is not a simulation. It is mearly image processing of the standard form to allow us to see what is there in radio-wavelengths. Nick Beeson (talk) 02:17, 11 April 2019 (UTC)
 * True! Altough I was refering to a picture that was an *actual simulation*, i.e. not based on any measurements. As Tarl noted, it has already been removed again from the article. Sorry for the confusion --2A02:AA16:3882:3680:7CEF:CC6C:8208:3480 (talk) 09:01, 11 April 2019 (UTC)

Latest mass and distance estimates - July 2019
This recent article updates the mass estimate for the SMBH to (3.964±0.047±0.026) solar masses and the distance to 7946±50±32 parsec.

Published: Relativistic redshift of the star S0-2 orbiting the Galactic center supermassive black hole or freely available pre-print.

Could someone familiar with editing and citing in Wikipedia incorporate this.

Thanks, George Dishman (talk) 07:59, 1 September 2019 (UTC)
 * oRLY “3.9…” solar masses? This wikipedia is in English, . Four solar masses is a small stellar-mass black hole. Incnis Mrsi (talk) 09:48, 1 September 2019 (UTC)

Is the huge table really necessary?
I think it's against WP:INDISCRIMINATE to have the huge list in Sagittarius A*. I'll remove it in a couple of days unless anyone objects. Sam-2727 (talk) 00:44, 5 October 2019 (UTC)
 * Did you prefer the previous table, or would you have deleted that one too? Amaurea (talk) 05:11, 5 October 2019 (UTC)
 * I agree, that table is not necessary here at all. Honestly, I don't think there's much purpose to having any table there. I think we should have some text about the stars that have been used to infer SgrA*'s mass, but no table (or just a handful of them at most). - Parejkoj (talk) 21:07, 5 October 2019 (UTC)
 * Currently the disambiguation for the term "S stars", which can refer to the central cluster of stars orbiting Sagittarius A*, redirects to this page. How about moving this table to a new article dedicated to S-stars, making the disambiguation page link there, and then briefly describing their role in studying Sagittarius A* on this page, with a link to the S-star page for details? Amaurea (talk) 23:55, 5 October 2019 (UTC)
 * The previous table was in the article for 8 years, surviving through almost 1000 edits. It showed just how close the stars S2 and S14 get to the black hole and contained the information necessary to infer the surprising speeds these stars reach - several percent of the speed of light (10x faster than the Hypervelocity star US 708 which is often cited as the fastest known star). I found myself referring back to it several times over the years, and found it sufficiently useful that I wanted to contribute an improved version back to Wikipedia. So I finally went through the effort to contact the astronomers behind the numbers in the table to point me to updated numbers, which I then used to make an updated table with improved precision and more consistent data units. I therefore disagree strongly with Sam-2727 and Parejkoj's assertion that the table is pointless. However, a case could be made for moving it to a page specifically about the S-stars. Amaurea (talk) 00:37, 6 October 2019 (UTC)
 * A comment on this: it looks oversized. The basic point is that most of the stars in the table have periods well over 100 years, so only a small fraction of an orbit has been measured and those provide little constraint on the BH. Most of the useful information comes from the handful of "best" stars which have either completed a full orbit, or had a close peri-hole passage, since 1992. Suggest keep a top-10 table here and dump the rest into a separate page. TychosElk (talk) 21:14, 18 October 2019 (UTC)
 * I understand that the table is "useful" (for specific applications that is), but there are many useful data tables that I could put on wikipedia using that argument. I don't think wikipedia's purpose is to provide esoteric datatables. It is notable that these stars are moving very fast, but then why not just say that instead of providing the datatable? If one really wants to use the datatable, then you can simply refer to the source it comes from. Sam-2727 (talk) 16:18, 2 November 2019 (UTC)

Completing the chart
S0–102 should be in this chart. What name should it have ?

S0? or something else? --Io Herodotus (talk) 14:25, 16 January 2020 (UTC)


 * I agree that this is confusing. There are sadly two different naming schemes for these stars, used by two different groups that monitor them. In the scheme used in the current table, which is that used by the group with the most up-to-date numbers I could find, that star is called S55. We should find some way to fix this confusion, since some articles like the one you link to use the S0- naming system, while others, like S2 (star), use the S naming system. Maybe the table should have a column for alternate names, if we can find them. By the way, I undid your revision to the table because it broke the table layout, introducing two almost-empty rows. However, the star S62 looks very relevant for the table - we should add it if we find the rest of the information, and if not, it should at the very least be mentioned in the text before the table, considering that it's got the smallest semimajor axis of all of them. Amaurea (talk) 03:26, 20 January 2020 (UTC)
 * The link to S62 was removed, I put it back hoping someone will translate it.
 * I have tried to do something, that needs to be completed. I believe this chart should show the closest known stars of Sagittarius A*. S55 is the same object as SO-102, the orbital period is not the same as the one given above, probably because of the precession. --Io Herodotus (talk) 11:25, 20 January 2020 (UTC)
 * Thanks for adding the id2 column.
 * This paper from 2016 is the source for the orbital period of 12.8 years for S55. It has an uncertainty of 0.1 years. The wikipedia page for S0-102 gives an orbital period of 11.5±0.3 years based on a 2012 article. The two periods are inconsistent, even taking into account the uncertainty. However, since the 12.8 year measurement is more recent and more precise, I suggest that we use that number. While it's possible to have two numbers in the same cell in the table, it makes it hard to interpret in terms of the other columns. For example, the next column in the table gives the uncertainty for the period, but it's not clear which of the numbers in the period column that number applies to. Having multiple numbers per column can also mess up sorting of the table. I'll remove the older number from the table cell, but how about we list both of them in the actual S0-102 page (which I think should be moved to S55, but oh well)? Amaurea (talk) 13:01, 20 January 2020 (UTC)

diameter
". . . this yields a diameter of 60 million kilometres." — Is this saying that the diameter of the black hole at the center of the Milky Way galaxy is 60 million kilometres? Google tells me something about 23.6 million kilometers. I don't really know this topic at all, by the way. I just don't understand what is what and if there is a disagrement of information or. . . what all. — Preceding unsigned comment added by Kibbled Jive Elk Zoo (talk • contribs) 12:41, 7 October 2020 (UTC)

Proof
Please do not change the introduction to add doubt about the black hole; doing so is publishing original research. If you harbor doubts, then publish a paper in a reputable science journal, and get someone else to add your doubts with reference to that paper.

There use to be doubt, but time and data move on. This issue is entirely settled. If you do not agree, I repeat, find a counter-paper, published after the 2018 paper by Abuter, et al. Since Abuter was published no paper has been published in a reputable science journal that expresses any doubt. In fact, many papers have been published since Abuter that explicitly speak about the Sagittarius A* black hole, many in the title, and no one has challenged this in print. Nick Beeson (talk) 13:35, 19 August 2020 (UTC)
 * I'd suggest that wording this as proof is incorrect, at least as I understand the term. Note that the reference you cite does not use the word "proof". We certainly have consensus (nothing else we know matches the parameters), but as best I know, we do not have a solid reference proving that the 4-million solar mass is a black hole. Note that matching some predictions for a black hole does not itself prove it is a black hole - after all, my TV matches some predictions for black magic, but that does not prove the existence of black magic. It's pedantry, but in an encyclopedia, important pedantry to avoid naming a "proof" when that doesn't exist. Tarl N. ( discuss ) 19:30, 19 August 2020 (UTC)
 * Agreed. For example, para 2 sentence 1 says "have been used to prove the presence of", but the cited source says "has found the strongest evidence yet". I would change the first sentence in para 2 to "Observations have...provided evidence for..." and the second sentence to "Evidence that..." (or "Further evidence that..." or even "Strong evidence that..."). Schazjmd   (talk)  19:48, 19 August 2020 (UTC)
 * I restored the original text until we come to a consensus on the proper phraseology. The original text, while somewhat wordy, I think correctly summarizes the current state of knowledge: Observations of a number of stars orbiting around Sagittarius A*, most notably the star S2, have been used to provide evidence for the presence of, and produce data about, the Milky Way's hypothesized central supermassive black hole, and have led scientists to conclude that Sagittarius A* is beyond any reasonable doubt the site of that black hole. Do we want to trim that down, or just leave it as is? <b style="color:green">Tarl N.</b> ( discuss ) 19:56, 19 August 2020 (UTC)
 * I would split it up. Observations of a number of stars orbiting around Sagittarius A*, most notably the star S2, have been used to provide evidence for the presence of, and produce data about, the Milky Way's hypothesized central supermassive black hole. Scientists have concluded that Sagittarius A* is beyond any reasonable doubt the site of that black hole. Schazjmd   (talk)  20:03, 19 August 2020 (UTC)
 * How about: Observations of a number of stars orbiting around Sagittarius A*, most notably the star S2, have been used to determine the mass and upper limits on the radius for the object. and Based on mass and increasingly precise radius limits, astronomers have concluded beyond reasonable doubt that Sgr A* is the Milky Way's central supermassive black hole. It's more definitive, matching the current consensus in Astronomy, while avoiding the claim of proof. <b style="color:green">Tarl N.</b> ( discuss ) 20:46, 19 August 2020 (UTC)
 * Works for me. We should give time to weigh in.  Schazjmd   (talk)  21:19, 19 August 2020 (UTC)
 * I like the suggestion of Tarl N. Let us please use it. It expresses my thoughts on the topic better than I did. Nick Beeson (talk) 22:35, 20 August 2020 (UTC)
 * I also agree with 's wording. - FlightTime  ( open channel ) 22:44, 20 August 2020 (UTC)

Sounds like consensus. Updated the lede accordingly. <b style="color:green">Tarl N.</b> ( discuss ) 16:12, 21 August 2020 (UTC)

Well I should have waited one month. Yesterday the Nobel Prize in Physics was awarded to Andrea Ghez and Reinhard Genzel specifically for demonstrating that Sagittarius A* is a black hole. Twenty hours later I came here to this article, and now the consensus result of this talk-subsection has been voided and all qulifiers-of-doubt, that Sagittarius A* is a black hole, have been removed from this article. I was correct in stating, 48 days ago, that "This issue is entirely settled."Nick Beeson (talk) 13:52, 7 October 2020 (UTC)
 * The key point you seem to be missing is the difference between "consensus" and "proof". Right now, most astrophysicists will agree that Sgr A* marks the location of a supermassive black hole, but that is NOT proof. <b style="color:green">Tarl N.</b> ( discuss ) 22:01, 7 October 2020 (UTC)

Sagittarius A* is the center of galaxy?
In this and a number of articles, for example "Supermassive black hole", it is written "the Milky Way galaxy has a supermassive black hole at its center" or similar. Can we conclude that the black hole is the center of the Milky Way. The center of the galaxy should be defined as the point which everything rotates around, and that has to be the black hole, or?--BIL (talk) 10:55, 11 October 2020 (UTC)
 * That would require defining "center". Center of mass, geometric center, ...? Either way, requiring research which does not exist yet.
 * Saying "it is at the center" is slightly different than saying "it is the center" - E.g., in the Solar System, the center of the Solar system is sometimes considered to be the Sun, sometimes considered to be the barycenter, which is slightly offset from the sun. We'd have a similar problem with the milky way, as well as the geometric center issue, but we simply don't have the information to describe either. <b style="color:green">Tarl N.</b> ( discuss ) 20:20, 15 October 2020 (UTC)

Orbiting stars table
There's been some back-and-forth on the huge table in the Orbiting Stars section. Might I suggest that table (and associated text) could move into its own article (e.g., Sagittarius A* cluster), leaving only a few example stars in this article? <b style="color:green">Tarl N.</b> ( discuss ) 02:36, 14 October 2020 (UTC)
 * I agree that the table doesn't add a lot to this article. Certainly, we do not need more than one or two of them, if we want any at all. - Parejkoj (talk) 17:25, 15 October 2020 (UTC)
 * Agree its misplaced here, though valuable, so in favour of creating a dedicated article with expanded context. Ceoil  (talk) 22:48, 17 October 2020 (UTC)
 * Ok, I'll do that tomorrow. <b style="color:green">Tarl N.</b> ( discuss ) 01:34, 18 October 2020 (UTC)
 * That's great. Ceoil  (talk) 02:33, 18 October 2020 (UTC)
 * Initial trim and movement done. Still doing significant work on Sagittarius A* cluster, and will fill in the values for S4714 here momentarily. <b style="color:green">Tarl N.</b> ( discuss ) 01:46, 19 October 2020 (UTC)
 * In filling out the data for S4714, Peißker et.al. give the semi-major axis as 4.079 mpc. On page 5, below table 1, they provide a conversion of $$0.04 pc \approx 1000 mas$$, so I converted the 4.079 mpc to 0.102 arcseconds to fit the table. <b style="color:green">Tarl N.</b> ( discuss ) 02:12, 19 October 2020 (UTC)

As a side note, we should probably update the 2011-era diagram of the star cluster orbits - those stars are no longer the most interesting. I chose the stars to remain in the local table based on presence in that diagram, but it's fairly obsolete. The "S62 and S4711..." article above has a current diagram on page 6, but I'm not sure of the ins-and-outs of making a new diagram based on that. Even trying to upload a screen shot for discussion defeated me (I tried "fair use", and it refused to allow fair use on a talk page). <b style="color:green">Tarl N.</b> ( discuss ) 02:43, 19 October 2020 (UTC)

I'm removing a dubious citation
I'm about to remove this citation: ref> ref> I think it's dubious. I got very excited by the title, as that would be one heck of an achievement. So I sat down to read the paper... It's got a decent intro ... and mentions a long string of correct keywords. But they are just that ... strings of keywords, followed by their textbook definition. Like ... gamma matrices ... is the author really unaware of spin connections which is what he seems to be struggling to explain? Or vielbeins, which is what he seems to want to make use of? We've got articles in WP on this stuff. It's just not that hard or complicated. Beyond the bare-bones definitions, nothing in that paper is articulated. The eqns aren't connected to each other. I agree that the paper lists mostly all of the appropriate, plausible ingredients that one might need for a "covariant canonical quantization", but the paper doesn't actually do that. It' doesn't do what the title (and abstract) claim. By the last 1/3rd of the paper ... about entropy and bits, the stuff about Sag A* seems .. utterly implausible. If I've missed something here, and someone could explain it, I'd love that (not joking; I know this material.) 67.198.37.16 (talk) 00:06, 15 November 2020 (UTC)

Sagittarius A* Mass & Spin
I added... "Supermassive black holes are characterized by just two numbers: mass and spin, but have a critical influence on the formation and evolution of galaxies. The spin of Sagittarius A*, a 4-million-solar-mass black hole at the center of our Milky Way Galaxy...'For our study we used the recently-discovered S-stars to show that the spin of Sagittarius A* must be smaller than 10% of its maximal value, corresponding to a black hole spinning at the speed of light,' (~30,000 km per second/~18,628.2 miles per sec)" - Harvard University Professor Avi Loeb<ref]Astrophysical Letters</ref] and http://www.sci-news.com/astronomy/sagittarius-a-spin-08993.html#:~:text=The%20spin%20of%20Sagittarius%20A%2A%2C%20a%204-million-solar-mass%20black,the%20distribution%20of%20the%20S-stars%20in%20its%20vicinity. 2601:589:4801:5660:E8CC:F2F6:C703:980C (talk) 01:36, 12 June 2021 (UTC)


 * I removed your edit. The edit you made states that the spin is 30,000 km/s, while the source states it is less than 10% of c (that the speed could NOT be that high, not that it IS that high). As an aside, spin of an object is usually not measured in linear distance per time - that article is simply using that measure as an upper limit because of the physical constraint of light-speed. Lastly, if you need to use two different forms for a single measurement, please use the convert template. The general convention is to say something like 30,000 km/s, resulting in "30,000 km/s". <b style="color:green">Tarl N.</b> ( discuss ) 04:53, 12 June 2021 (UTC)

Date of Cluster Chart
The article text referencing the date of the chart showing the cluster of stars around SgrA* indicates 2011, but the chart itself indicates 2005 on the footnote. I am easily confused, but from what date is the data on the chart - are the orbits and coordinates shown on it from 2005 or 2011? Tesseract501 (talk) 05:47, 30 November 2021 (UTC)
 * You might want to check out Sagittarius_A*_cluster, a more complete chart with more details on what data arrived from which sources. <b style="color:green">Tarl N.</b> ( discuss ) 06:09, 30 November 2021 (UTC)

G2
G2 appears not to be a dust cloud but consists likely of three protostars (age less than 1 My) within a dust cloud. For this reason G2 was not destroyed at its approach to Sgr A*.
 * https://iopscience.iop.org/article/10.3847/1538-4357/ac23df

--Ernsts (talk) 17:10, 14 December 2021 (UTC)

2017 vs 2022 image
There's already confusion in the edit history about this, which I noticed because I wanted to go in and correct the date on the picture before I realised I was wrong. Both the image capture and image release date are mentioned in the article but it's not in context of each other. Could somebody re-write the final paragraph in the lede so it's not confusing to people reading that and looking at the picture on the right and being very confused? Same goes for the final paragraph in the first section of the page. I'd edit it myself but I don't understand the technical details and so lack the knowledge to phrase it correctly.

137.111.13.103 (talk) 01:59, 13 May 2022 (UTC)


 * Someone has fixed this now, thanks! 137.111.13.103 (talk) 07:18, 13 May 2022 (UTC)

photograph or image?
The last paragraph of the introduction says " ... released a photograph of Sagittarius A* ...". Wouldn't "image" be more accurate than "photograph"? Bubba73 You talkin' to me? 03:36, 14 May 2022 (UTC)


 * @Bubba73, you are right. I have changed it. StarryGrandma (talk) 13:50, 14 May 2022 (UTC)
 * The image was created through aperture synthesis. A reference that explains how this is done for Sag A* is: — Preceding unsigned comment added by StarryGrandma (talk • contribs) 15:01, 14 May 2022 (UTC)

The discovery was considered "exciting".
Can someone please clarify whether the excitement mentioned in the lede, in the above statement, means that the discovery was "exciting" to astronomers and the general public, i.e. wonderful, brilliant news, or whether "exciting" is a technical term related to the term "excited state"? - BobKilcoyne (talk) 00:27, 14 May 2022 (UTC)


 * From the history section of article- "The name Sgr A* was coined by Brown in a 1982 paper because the radio source was "exciting", and excited states of atoms are denoted with asterisks.[35][36]
 * I know one editor tried to remove this from lede but was promptly reverted. While there's eyes on it, might be a good time to discuss Slywriter (talk) 01:00, 14 May 2022 (UTC)
 * As a member of the general public, I read this as Brown was making a pun or joke by doing this. But now I am wondering if that's not the case? Lessthanideal (talk) 23:40, 14 May 2022 (UTC)
 * I assumed that was a given. Astronomers are prone to this sort of fun when picking names for objects.  Lithopsian (talk) 13:29, 15 May 2022 (UTC)
 * Just a note that I found File:SgrA2018.gif awesome! — Paleo  Neonate  – 16:01, 15 May 2022 (UTC)

Semi-protected edit request on 15 May 2022
Please change the sentence at the beginning of the section "Observation and description":

"On May 12, 2022, the Event Horizon Telescope, for the first time, released a photograph of Sagittarius A*, based on direct radio images which were taken in 2017, and confirming the object to contain a black hole."

to

"On May 12, 2022, the Event Horizon Telescope Collaboration, for the first time, released a photograph of Sagittarius A*, based on direct radio images taken in 2017, and confirming the object to contain a black hole."

Reasoning: A telescope cannot release a photo, astronomers can. The sentence can be simplified, by removing the phrase "which were". 109.241.162.167 (talk) 18:59, 15 May 2022 (UTC)
 * ✅. You are correct, I have changed it. And it is not a photograph, nor is it based on direct radio images. Thanks for this request. StarryGrandma (talk)

"For the first time"
The first sentence of the article body begins "On May 12, 2022, the Event Horizon Telescope Collaboration, for the first time, released an image of Sagittarius A* ...". I can't parse what "for the first time" is supposed to mean in this sentence. I think, based on my general knowledge rather than based on the sentence itself, that it's supposed to mean this is the first image ever produced of Sgr A* by anyone. But it reads more like it's saying this is the first time that this collaboration has released an image of Sgr A*, or possibly that it's the first time that this collaboration has released an image of any black hole, or even that it's the first time they've released any image. I'm not sure what's intended, so I'd ask that someone who knows what is intended here fix the wording to be less ambiguous. CodeTalker (talk) 17:47, 16 May 2022 (UTC)
 * I've been watching the changes and had the same confusion about "first time". Maybe we could reword? On May 12, 2022, the first image of Sagittarius A* was released by the Event Horizon Telescope Collaboration. The image, which is based on radio interferometer data taken in 2017, confirms that the object contains a black hole. Schazjmd   (talk)  17:53, 16 May 2022 (UTC)
 * Sounds good and clearer to me. StarryGrandma (talk) 19:28, 16 May 2022 (UTC)
 * Done. CodeTalker (talk) 15:20, 21 May 2022 (UTC)

"Conversion from micro arc seconds to meters"
Sgr A* is 26,000 light-years from earth, and a circumference of a circle with that radius is 2pix26,000 light-years = 163,363 light years (ly). A light year is 2.998x10^8 m/s x 365.24 days/year x 24 hours/day x 3600 s/hour = 9.461x10^15 m. An arc-degree is 1/360 of the circumference, and a micro-arc-second is (1/3600)x10^-6 of that, resulting in a diameter of 163,363 ly x 9.461x10^15 m/ly x 51.8 x 10^-6/(360x3600) = 6.18x10^10 m, not 5.18x10^10 m. This also results in 38.4 million miles, not 32.2 million miles. — Preceding unsigned comment added by Delbert7 (talk • contribs) 14:08, 10 February 2023 (UTC)

Featured picture scheduled for POTD
Hello! This is to let editors know that File:EHT Saggitarius A black hole.tif, a featured picture used in this article, has been selected as the English Wikipedia's picture of the day (POTD) for May 12, 2023. A preview of the POTD is displayed below and can be edited at Template:POTD/2023-05-12. For the greater benefit of readers, any potential improvements or maintenance that could benefit the quality of this article should be done before its scheduled appearance on the Main Page. If you have any concerns, please place a message at Wikipedia talk:Picture of the day. Thank you! --Ahecht (<span style="color:#FFF;background:#04A;display:inline-block;padding:1px;vertical-align:-.3em;font:bold 50%/1 sans-serif;text-align:center">TALK PAGE ) 16:04, 25 February 2023 (UTC)

Split proposal for Sagittarius A*
This section of the article is disproportionately long compared to other objects orbiting Sagittarius A*, so I'd recommond splitting this content to a new article on top of the redirect G2 gas cloud. –<b style="color:#77b">Laundry</b><b style="color:#fb0">Pizza</b><b style="color:#b00">03</b> ( d c̄ ) 09:55, 4 April 2023 (UTC)
 * Agree. Good idea. 67.198.37.16 (talk) 03:39, 4 June 2023 (UTC)


 * Support, since the section is pretty long.
 * 117daveawesome (talk) 13:11, 30 September 2023 (UTC)
 * Split. The section is somewhat long (like previously stated)
 * Atlantlc27Lol (talk) 14:16, 31 December 2023 (UTC)