by Ann » Wed Nov 18, 2020 7:54 pm
BDanielMayfield wrote: ↑Wed Nov 18, 2020 6:12 pm
johnnydeep wrote: ↑Wed Nov 18, 2020 3:49 pm
So, the "double cluster" link to Wikipedia -
https://en.wikipedia.org/wiki/Double_Cluster - acts like this is the only double cluster known to exist. Is that true? Google searches for "double star cluster" also seem to imply that there is only one. Do we really not know of any others? And for that matter, considering the proliferation of double, triple, and higher multiple star systems, I would think there should be lots of double and even triple clusters out there.
Based on your search Johnny this probably is the only example of such a pairing in our limited field of view. Other pairs of clusters could certainly exist in parts of the MW that are blocked from our vantage.
But these are
open star clusters, which means that the individual stars are unbound, and so are dispersing over time. Open star clusters are therefore transitory phenomena. And if the stars are unbound gravitationally, I’d guess that these two clusters aren’t bound together either.
Bruce
Interesting observation about the dispersal of open clusters, Bruce. I actually think that h and chi Persei stand a better chance than most open clusters to stay moderately intact for a long time. These clusters are massive as open clusters go, and they are located in the Perseus arm, at a fairly safe distance from the sound and the fury of the inner parts of the Milky Way.
Anyway, I was reminded of a fascinating "double cluster" among globulars, M53 and NGC 5053. Even their designations sound vaguely fraternal. These two globulars are situated quite close to one another in the sky, and there is a bridge of material between them, so there is some interaction going on between them.
Both globulars are extremely metal-poor, especially NGC 5053.
Wikipedia wrote about NGC 5053:
This is a metal-poor cluster, meaning the stars have a low abundance of elements other than hydrogen and helium—what astronomers term metallicity.
As recently as 1995, it was considered the most metal-poor globular cluster in the Milky Way.The chemical abundances of the stars in NGC 5053 are more similar to those in the dwarf galaxy Sagittarius Dwarf Spheroidal Galaxy than to the Milky Way halo. Along with the kinematics of the globular cluster, this suggests that NGC 5053 may have been stripped from the dwarf galaxy.
Wikipedia wrote about M53:
This is considered a metal-poor cluster and at one time was thought to be the most metal-poor cluster in the Milky Way.
So both these clusters are metal-poor, but their metallicity is clearly not the same, so I find it unlikely that they were born out of the same nebula. And I find it very hard to believe that these two clusters have orbited the center of the Milky Way in tandem for as long as they have existed. Because these are a pair of Methuselahs, some 12.67 billion years for M53 and 12.3±0.7 billion years for NGC 5053, according to Wikipedia.
Just think: The two clusters of the Double Cluster of Perseus are believed to be 12.8 million years old.
Well, M53 and NGC 5053 are about a thousand times older.
Ann
By the way, the oldest of the Messier open clusters, M67, is located in or near the Perseus arm of our galaxy, or so I believe. M67 is some ~4 billion years old and located pretty far away from the hustle and bustle of the center of the Galaxy. As are h and chi Persei.
[quote=BDanielMayfield post_id=308184 time=1605723123 user_id=139536]
[quote=johnnydeep post_id=308177 time=1605714581 user_id=132061]
So, the "double cluster" link to Wikipedia - https://en.wikipedia.org/wiki/Double_Cluster - acts like this is the only double cluster known to exist. Is that true? Google searches for "double star cluster" also seem to imply that there is only one. Do we really not know of any others? And for that matter, considering the proliferation of double, triple, and higher multiple star systems, I would think there should be lots of double and even triple clusters out there.
[/quote]
Based on your search Johnny this probably is the only example of such a pairing in our limited field of view. Other pairs of clusters could certainly exist in parts of the MW that are blocked from our vantage.
But these are [u]open[/u] star clusters, which means that the individual stars are unbound, and so are dispersing over time. Open star clusters are therefore transitory phenomena. And if the stars are unbound gravitationally, I’d guess that these two clusters aren’t bound together either.
Bruce
[/quote]
[float=left][img3="Diffuse globular cluster NGC 5053 (left) and rich globular cluster M53 (right). Photo: Bart Delsaert."]https://delsaert.files.wordpress.com/2019/04/m53_lrgb.jpg?w=768&h=768[/img3][/float]
Interesting observation about the dispersal of open clusters, Bruce. I actually think that h and chi Persei stand a better chance than most open clusters to stay moderately intact for a long time. These clusters are massive as open clusters go, and they are located in the Perseus arm, at a fairly safe distance from the sound and the fury of the inner parts of the Milky Way.
Anyway, I was reminded of a fascinating "double cluster" among globulars, M53 and NGC 5053. Even their designations sound vaguely fraternal. These two globulars are situated quite close to one another in the sky, and there is a bridge of material between them, so there is some interaction going on between them.
Both globulars are extremely metal-poor, especially NGC 5053.
[quote][url=https://en.wikipedia.org/wiki/NGC_5053]Wikipedia[/url] wrote about NGC 5053:
This is a metal-poor cluster, meaning the stars have a low abundance of elements other than hydrogen and helium—what astronomers term metallicity. [color=#0040FF][b]As recently as 1995, it was considered the most metal-poor globular cluster in the Milky Way.[/b][/color]The chemical abundances of the stars in NGC 5053 are more similar to those in the dwarf galaxy Sagittarius Dwarf Spheroidal Galaxy than to the Milky Way halo. Along with the kinematics of the globular cluster, this suggests that NGC 5053 may have been stripped from the dwarf galaxy.[/quote]
[quote][url=https://en.wikipedia.org/wiki/Messier_53]Wikipedia[/url] wrote about M53:
This is considered a metal-poor cluster and at one time was thought to be the most metal-poor cluster in the Milky Way.[/quote]
So both these clusters are metal-poor, but their metallicity is clearly not the same, so I find it unlikely that they were born out of the same nebula. And I find it very hard to believe that these two clusters have orbited the center of the Milky Way in tandem for as long as they have existed. Because these are a pair of Methuselahs, some 12.67 billion years for M53 and 12.3±0.7 billion years for NGC 5053, according to Wikipedia.
Just think: The two clusters of the Double Cluster of Perseus are believed to be 12.8 million years old. 👶👶 Well, M53 and NGC 5053 are about a thousand times older. 👴🏻👴🏻
Ann
[float=left][img3="Old open cluster M67. Photo: Bob Franke."]https://lh3.googleusercontent.com/proxy/i2EUSIgxwrX4TOwifMSC25PqTMqTQ6iLrszBPAIvFjimT5Mnv6fnphDhi5d_X8ohnbxnccuztYkwfo4O5Q[/img3][/float]By the way, the oldest of the Messier open clusters, M67, is located in or near the Perseus arm of our galaxy, or so I believe. M67 is some ~4 billion years old and located pretty far away from the hustle and bustle of the center of the Galaxy. As are h and chi Persei.