I How accurate is the distance to M4 and its stars according to different sources?

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The discussion centers on the varying estimates of the distance to Messier 4 (M4) and its stars, with figures ranging from 5,500 to 12,400 light-years. The accuracy of Gaia's measurements of radial distances and peculiar motions of stars within M4 is questioned, particularly regarding their orbits and eccentricities. There is confusion over the classification of PSR B1620−26, with some sources listing it as a member of M4 while others suggest it is a background object, leading to discrepancies in distance measurements. The conversation highlights the need for clarity on Gaia's capabilities in measuring peculiar accelerations in globular clusters. Overall, the inconsistencies in distance estimates raise concerns about the reliability of current data on M4.
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How far is M4? I have seen contradictory numbers for M4 and stars in it.
How precise is Gaia in measuring the radial distances to various stars in M4? Their radial position relative to each other? Their peculiar motions?
What kinds of orbits do stars in the outskirts of M4 follow? High eccentricity orbits that bring them to cluster interior on each periapse, or low eccentricity orbits that stay on the outskirts of cluster all along?
Does Gaia have the precision to measure peculiar accelerations of stars in globular clusters?
 
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snorkack said:
I have seen contradictory numbers for M4 and stars in it.
Where?
 
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malawi_glenn said:
Where?
This:
https://en.wikipedia.org/wiki/Messier_4
offers 7200 ly, (2200 pc) with reference to
https://ui.adsabs.harvard.edu/abs/1985A&A...143...8C
But it also claims PSR B1620−26 as a member (rather than a background object), reference to https://esahubble.org/images/potw1236a/
This:
https://en.wikipedia.org/wiki/PSR_B1620−26
claims the distance to PSR B1620−26 as 3800 pc (12 400 ly), source:
http://exoplanet.eu/catalog/psr_b1620-26_(ab)_b/
This:
https://www.eso.org/public/images/m4/
quotes 5500 ly
5500 ly and 12400 ly is a gross difference. Does Gaia have any comment?
 

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