Talk:Local Group

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Stars

Do we have any idea of how many stars might be in the Local Group? -- Tarquin 07:19, 2 May 2005 (UTC)[reply]

There are about 10^11 stars in the Milky Way (See, for example, Binney & Tremaine, page 1) so figure for the group we're talking around 10^12, within a factor of about 3 or so. Even the number of stars in the Milky way contains a lot of conjecture, so I wouldn't expect a longer search to give a more exact number.--WilyD 8:45, Sept 29 2005 (EST)

Map

Where does the map come from? Who made it? What about taking the 3D map used in the german article?--CWitte 14:43, 9 Jun 2005 (UTC)

I would say the German map is better, but I don't know what other people have to say about that.DaMatriX

The map is from "Atlas of the Universe", without the z=0 plane drawn in. It does not list all the galaxies mentioned in the article. Those very close to the Milky Way await zooming in at the Atlas site, and some don't show at all, like [I]And IV[/I]. I don't find it at all useful. Someone should feed the coordinates into a general purpose (and free) 3D viewing program. —Długosz 14-Sept-2007. —Preceding unsigned comment added by Długosz (talk • contribs) 16:29, 14 September 2007 (UTC)[reply]

(Joseph M. Newcomer) I observe that the name of the Canis minor galaxy is called "Canes" — Preceding unsigned comment added by 71.112.174.11 (talk) 18:11, 19 June 2018 (UTC)[reply]

Merge from List of nearest galaxies

The following discussion is closed. Please do not modify it. Subsequent comments should be made in a new section.

OPPOSE a list is useful by itself, and would clutter the Local Group article. And not everything on the list need be a Local Group member. 132.205.45.110 22:37, 13 January 2006 (UTC)[reply]
OPPOSE "Local Group" is an established astronomical term, with a clear definition of its member galaxies. A list is nice, but only as an additional overview, and might describe either more or less galaxies (depending on the range) than the Local Group. --84.178.157.201 11:19, 18 January 2006 (UTC)[reply]
OPPOSE I agree, it should remain separate. --JorisvS 12:00, 27 May 2006 (UTC)[reply]

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

(Joseph M. Newcomer) I notice the mass of M110 is "9.3 solar masses". Shouldn't that be "9.3 billion solar masses"? — Preceding unsigned comment added by 71.112.174.11 (talk) 18:14, 19 June 2018 (UTC)[reply]

More dwarf galaxies

Two more faint local group dwarfs - [1] - one in Canes Venatici, the other in Bootes. -- ALoan (Talk) 10:59, 10 May 2006 (UTC)[reply]

There's another one to add... Leo T [2] 70.55.86.251 (talk) 08:36, 18 July 2008 (UTC)[reply]

This web page, [3], lists over 50 galaxies (I counted 54). However, the Wikipedia page says that there are only 30 galaxies in the Local Group including dwarf galaxies. Other web sites also say there are at least 45. This needs to be changed. Collinberickson (talk) 00:01, 23 March 2010 (UTC)Collinberickson[reply]

There might be a great many more. See "A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy" [4] I believe that the article was in Nature, nearly 3 years ago. The maps show about 3 dozen. agb

Size and distance

It's a nice, useful list. However, I miss certain things, especially the distance to the Milky Way Galaxy and the size of the Galaxy. It would a better list with this information. --JorisvS 12:02, 27 May 2006 (UTC)[reply]

Care to elaborate? The distance to the Milky way galaxy isn't an obvious number (perhaps zero, up to - 8kpc? maybe). And who cares what size the individual galaxies are? That's why they have individual articles .... isn't it? WilyD 22:43, 7 November 2006 (UTC)[reply]

hi Guys,

Says size of Milki Way is : Diameter: 175±25 kly, mass: (1.3±0.3)×10^12 M☉, number of stars: (2.5±1.5)×10 for Andromeda : at about 125% of the mass of the Milky Way.[2] Diameter: 220 kly, mass: (1.15±0.35)×10^12 M☉, number of stars: ca. 1012

Now seems to me mass of 1.3*10^12 is greater than 1.15*10^12, yet it says Andromeda is 125% of mass??? And why the hec is Milky way so heavy/dense. And Milky way is only 100k ly Across. Source= Elite: Dangerous galaxy map.

Now if Andromeda is 200k ly Across and Milky way is 100k ly across, should be Andromeda is 8x size(mass) of milky way yet that is not the case?

What is going on here with these figures ?

I am not a wikipedia guy btw I never edit, just looking at these figures and they are "off".

gjb786

Around how many stars total?

"Number of stars 200 to 400 billion" That is for the Milky Way; what about for the Local Group? --Emesee (talk) 15:53, 22 June 2008 (UTC)[reply]

See above - should be about a trillion.--Roentgenium111 (talk) 18:38, 9 June 2011 (UTC)[reply]

What is in the center?

Which gravitational force could be in te center? I don't assume these galaxies turn around each other?--80.200.214.233 (talk) 22:57, 10 September 2008 (UTC)[reply]

The mutual attraction of all the galaxies makes the group hold together. IIRC, the "center" is relatively empty at the moment. But the central volume contains the Milky Way, Andromeda and Triangulum. 76.66.193.90 (talk) 10:04, 22 February 2009 (UTC)[reply]

Check out Barycentric coordinates (astronomy) and Center of mass. 99.225.180.228 (talk) 21:34, 16 May 2012 (UTC)[reply]

Actually i think this users question was ment to be "where" is the center? if that is the case i would have to agree with USER ip 99.225.180.228. i learned sometime ago i forgot when but many years ago when i was a kid in the early 1990's that Andromada was the galaxy that actually was moving towards the milky way. if this is true then the center of our known universe would be at a point that in between the two galaxys. Also by the end of the 1990s i learned of triangulum galaxy and that its also nearby. i do know that it takes the solar system about 250 million years to orbit the milky way. in about 1 billion years or 4 galactic revolutions the andromeda and milky way will begin to merge. asuming that this is true whats triangulum going to do in about 1 billion years? also a side question if triangulum is the second most distant major galaxy whats the 3rd distant major galaxy called and where would it be located on the local group map? 76.253.136.175 (talk) 06:19, 3 January 2013 (UTC)[reply]

Aquarius Dwarf

Why is Aquarius Dwarf a probable non-member? --84.43.145.225 (talk) 01:05, 14 June 2009 (UTC)[reply]

Iron content graph

I don't see what connection this graphic has to the rest of the article. Nor do I understand what is being graphed. What is the x-axis? —Preceding unsigned comment added by 76.170.159.92 (talk) 00:07, 4 May 2010 (UTC)[reply]

Local Group in 1971

interestingly... the Local Group was thought to be composed of 7 galaxies in 1971 [5] -- Milky Way, Andromeda, Maffei 1&2, and three others (presumably M33, LMC, SMC) 65.94.47.63 (talk) 10:52, 9 June 2011 (UTC)[reply]

Mass of Local Group?

The estimated mass for the local group is the same figure given as the mass of the Milky Way on its page, around 10^12 M☉. One must be incorrect? — Preceding unsigned comment added by 134.161.8.15 (talk) 21:03, 24 April 2012 (UTC)[reply]

I noticed the same thing (plus the listed mass of the Milky Way plus Andromeda is > the Local Group, which can't be right). In addition, this article claims that we know the mass of the local group much more precisely than the Milky Way article claims we know the its mass. Something has to give. — Preceding unsigned comment added by 131.107.0.81 (talk) 00:27, 5 September 2012 (UTC)[reply]

I think the numbers are close because the Milky Way and the Andromeda Galaxy make up almost the entire mass of the group (i.e. there are many other galaxies, but they are MUCH smaller). The Karachentsev paper (where the local group estimate of 1.29×10^12 solar masses comes from) mentions 5.8×10^11 and 7.1×10^11 solar masses for the Milky Way and Andromeda, respectively. Those estimates are somehow derived from the local group mass estimate, however, instead of a method focused solely on the Milky Way. 128.146.32.139 (talk) 22:26, 3 December 2013 (UTC)[reply]

One recent estimate of the LG mass can be found in the ApJ paper "On the Mass of the Local Group", Gonzalez et al. 2014(http://arxiv.org/abs/1312.2587). MMW,200+MM31,200= 2.40+1.95−1.05×1012M⊙ (90% confidence interval), and the DM mass within 1mpc, MLG(r<1Mpc)=4.2+3.4−2.0×1012M⊙ (90% confidence interval). — Preceding unsigned comment added by 186.103.163.28 (talk) 12:49, 16 December 2014 (UTC)[reply]

Is it true that most of the group's mass is concentrated in Milky Way and Andromeda? If so, how much? 90%? 95%? This is vital information that should be included in the article. It was hard to find information about it outside Wikipedia, and what I did find was full of astronomical jargon and I could not understand it. — Preceding unsigned comment added by Nnnu (talk • contribs) 21:14, 18 March 2018 (UTC)[reply]

@Nnnu. I think it's almost certainly true, because most estimates that exist pin the satellite galaxies as tens or hundreds of times less massive than the Milky Way or Andromeda. However it's difficult to pin down a reliable source of this—all of these mass estimations are very rough, and most of the smaller galaxies in the LG don't have mass estimations for them specifically. One source I've seen is this: http://www.messier.seds.org/more/local.html (though it disagrees with some of the other sources I've seen, so it's hard to know how correct it is).

One notable recent estimate of the Milky Way Galaxy pins it at about 1.5×10^12 solar masses (https://iopscience.iop.org/article/10.3847/1538-4357/ab089f), which makes it about twice as massive as the most recent estimate of Andromeda, about 8×10^11 solar masses. This seems reasonably in-line with what is currently reported (the entire group being "on the order of 2×10^12 solar masses"), though the later part of the article contains notable errors in this regard (Andromeda is clearly not about 125% the mass of the Milky Way, at least not by current estimates).

One caveat: our "best known estimates" changes pretty much every year or two. In short—most of this information is highly uncertain. Regardless, it's probably worth reporting (but of course it must be updated fairly regularly, and it should not be written as if the facts are well-established). The Town Idiot (talk) 06:20, 23 July 2019 (UTC)[reply]

Magellanic spirals

Should we mention that the Large Magellanic Cloud and NGC 3109 are possible Magellanic spirals?©Geni (talk) 16:21, 2 January 2014 (UTC)[reply]

Formation

Some information about the formation of the Local Group in a recent paper.

A Council of Giants Marshall L. McCall 2013 April 29 10.1093/mnras/stu199 http://mnras.oxfordjournals.org/content/early/2014/02/28/mnras.stu199

-- 70.50.151.11 (talk) 12:36, 12 March 2014 (UTC)[reply]

Group or cluster?

Should the article describe the Local group as a galaxy group or a galaxy cluster? I believe the former; the number of members (54) is closer to the accepted definition of a group than the "hundreds or thousands" that are the norm for a cluster. In addition to the Hubble quote already in the article that uses "group", I have other sources that agree with galaxy group, but figure it is preferable to try to gather editor consensus than to start an edit war. UnitedStatesian (talk) 03:27, 31 January 2015 (UTC)[reply]

It is absolutely a group. Do any sources call it a cluster? In fact, if we weren't inside it, it would barely even be called a group: from a significant distance away, it would look like a pair of galaxies (MW and M31), and nearly all the others would be too small to detect. I see that the article also calls it the Local Cluster. That's wrong. There is a Local Supercluster, but that is very different than the Local Group. —Alex (ASHill | talk | contribs) 11:46, 7 February 2015 (UTC)[reply]

Thanks, Alex, and thanks for making the edit. UnitedStatesian (talk) 16:51, 4 March 2015 (UTC)[reply]

Unresolvable clarify tag

The [clarify] tag on the History section in this version is bound to remain for a while as it is the phrasing used in the reference.

"In the 2/3 century since Hubble’s work, the number of known Local Group members has increased from 12 to 36 (see Table 1) by the addition of almost two dozen low-luminosity galaxies"

I'm removing the "almost two dozen" since I'm not really sure how to interpret it and the reference wasn't helpful.

–Erik.Bjareholt (talk) 16:08, 3 October 2016 (UTC)[reply]

gaia data

Article with some info on some of the dwarf galaxies

Gaia Data Release 2. Kinematics of globular clusters and dwarf galaxies around the Milky Way

https://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/201832698

Preprint at:

https://arxiv.org/abs/1804.09381

Wrong galaxy positions of first image

Hi, the first image (File:Local Group and nearest galaxies.jpg) may be very wrong. Because in this image, M31 position is higher than the milky way while LMC and SMC are shown lower than the milky way. We can see the map (https://en.wikipedia.org/wiki/File:Local_Group.svg) or the last big image in this article (https://commons.wikimedia.org/wiki/File:Earth%27s_Location_in_the_Universe.jpg) or,http://www.luratia.com/images/UM-Local-Group.jpg

In these picutres, M31 position is lower than the milky way. So very probably, the first image shows wrong relative position of M31 and the milky way. — Preceding unsigned comment added by Feiximing1983 (talk • contribs) 02:08, 14 June 2018 (UTC)[reply]

Speed of approach

In the introductory paragraph the relative speed of the two groups is given as 123 km/h ,whereas in the collision article (https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision) it is given as 110 km/s , several orders of magnitude different. I looked at the publicly available part of the reference for 123 km/h but it did not cover that (presumably it's in the paywalled part). Can this be resolved? — Preceding unsigned comment added by Old Wolf 2 (talk • contribs) 02:25, 12 April 2019 (UTC)[reply]

Several orders of magnitude? Are you serious? The difference if within the measurement error. Ruslik_Zero 17:56, 23 July 2019 (UTC)[reply]

123 km per hour is indeed several orders of magnitude away from 110 km per sec. But the former is almost certainly wrong: Astronomical speeds are routinely given in km/sec, and they are routinely triple-digit speeds (or more) in those units. 123 km per hour would probably be too small to measure (whereas the true relative of the two galaxies is certainly not too small to measure.) Jmacwiki (talk) 05:33, 25 July 2019 (UTC)[reply]