The brightest six members of the cluster are visible in 10×50 binoculars at magnitudes 6.9 and fainter, while fifteen evenly distributed stars are visible with a 25×100 pair.[11] More than two dozen stars are visible in an amateur telescope.[6] The average
extinctionAV due to
interstellar dust along the line of sight from the Earth is 1.20±0.24, with a color excess E(B−V) of 0.38±0.07.[8]
In total, 3,675 stars in the field of NGC 6530 have been catalogued as candidate members, with the likely members being 2,728.[3] As of 2019, 652 stars have been confirmed as members: 333 of these are classical
T Tauri-type
variable stars showing a
near infraredemission excess, while the remainder are weak T Tauri stars showing a photospheric excess.[9] Candidate stars appear in two main groups at the cluster core and the Sagittarius "Hourglass nebula", with other smaller concentrations. Two such minor concentrations are associated with the stars
7 Sgr and HD 164536.[3]
Age estimates for the members shows a spread in values that suggests more than one burst of
star formation. Initial star formation began up to 15 million years ago, but the bulk formed in the last 1–2 million years near the cluster center.[9]Astrometric data suggests the parent
molecular cloud collided with the
galactic plane some four million years ago, which may have triggered the star formation.[3] The dispersion of velocities for a sample of stars in the cluster suggests it may be
gravitationally unbound and there is evidence the star population is expanding, particularly to the north and south.[12]
^Wright, Nicholas J.; et al. (June 2019). "The Gaia-ESO Survey: asymmetric expansion of the Lagoon Nebula cluster NGC 6530 from GES and Gaia DR2". Monthly Notices of the Royal Astronomical Society. 486 (2): 2477–2493.
arXiv:1903.12176.
Bibcode:
2019MNRAS.486.2477W.
doi:
10.1093/mnras/stz870.