Messier 56 (also known asM56 orNGC 6779) is aglobular cluster in theconstellationLyra.[a] It was discovered byCharles Messier in 1779.[b] It is angularly found about midway betweenAlbireo (Beta (β) Cygni) andSulafat (Gamma (γ) Lyrae). In agood night sky it is tricky to find with large (50–80 mm) binoculars, appearing as a slightly fuzzy star.[9] The cluster can be resolved using a telescope with anaperture of 8 in (20 cm) or larger.[10]
M56 is about 32,900 light-years away fromEarth[3] and measures roughly 84 light-years across, containing 230,000[5]solar masses (M☉). It is about 31–32 kly (9.5–9.8 kpc) from theGalactic Center and 4.8 kly (1.5 kpc) above thegalactic plane.[11] This cluster has an estimated age of 13.70 billion years and is following a retrograde orbit through the Milky Way. The properties of this cluster suggest that it may have been acquired during the merger of adwarf galaxy, of whichOmega Centauri forms the surviving nucleus. For Messier 56, the abundance of elements other than hydrogen and helium, what astronomers term themetallicity, has a very low value of [Fe/H] = –2.00dex which is1⁄100 of the abundance in the Sun.[7]
The brighteststars in M56 are of 13thmagnitude, while it contains only about a dozen knownvariable stars, such asV6 (RV Tauri star; period: 90 days) orV1 (Cepheid: 1.510 days);[12] other variable stars are V2 (irregular) and V3 (semiregular). In 2000, a diffuse X-ray emission was tentatively identified coming from the vicinity of the cluster. This is most likelyinterstellar medium that has been heated by the passage of the cluster through the galactic halo. The relative velocity of the cluster is about 177 km s−1, which is sufficient to heat the medium in its wake to a temperature of 940,000 K.[13]
M56 is part of theGaia Sausage, the hypothesised remains of a merged dwarf galaxy.[14]
^Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters",Harvard College Observatory Bulletin,849 (849):11–14,Bibcode:1927BHarO.849...11S.
^abIvanov, Valentin D.; et al. (2000). "Near Infrared Photometry of Galactic Globular Clusters M56 and M15. Extending the Red Giant Branch vs. Metallicity Calibration Towards Metal Poor Systems".arXiv:astro-ph/0002118.
^ab"Messier 56".SEDS Messier Catalog. Retrieved29 April 2022.
^Pietrukowicz, P.; et al. (June 2008), "CURiuos Variables Experiment (CURVE): Variable Stars in the Metal-Poor Globular Cluster M56",Acta Astronomica,58:121–130,arXiv:0806.1515,Bibcode:2008AcA....58..121P
^Hopwood, M. E. L.; et al. (July 2000), "A possible detection of diffuse extended X-ray emission in the environment of the globular cluster NGC 6779",Monthly Notices of the Royal Astronomical Society,316 (1):L5–L8,Bibcode:2000MNRAS.316L...5H,doi:10.1046/j.1365-8711.2000.03717.x
^Specifically in the center-northwest of Lyra which makes it visible from everywhere above about the50th parallel south. However the Sun passes through Sagittarius far to the south (or technically the Earth orbits so as to make the Sun seem to do so) throughout December. This also makes the cluster mostly risen during day, not night, in the nearest months but will never impede pre-dawn and post-sunset views from the upper half of northerly latitudes.
