Messier 56
A low-metallicity globular cluster in Lyra with a retrograde orbit.
Messier 56 (M56, NGC 6779) is a globular cluster located in the constellation Lyra, discovered by Charles Messier in 1779. On the sky, it sits roughly halfway between the stars Albireo (Beta Cygni) and Sulafat (Gamma Lyrae). Under good conditions, it is a challenging target for large binoculars (50–80 mm), appearing as a slightly hazy star, and requires a telescope with an aperture of at least 8 inches (20 cm) to resolve individual stars.
The cluster lies about 32,900 light-years from Earth and spans roughly 84 light-years across, containing about 230,000 times the mass of the Sun. It is located approximately 31–32 thousand light-years (9.5–9.8 kiloparsecs) from the Galactic Center and about 4,800 light-years (1.5 kiloparsecs) above the galactic plane. Its estimated age is 13.70 billion years, and it follows a retrograde orbit through the Milky Way. These properties suggest M56 may have been acquired when the Milky Way merged with a dwarf galaxy, of which the globular cluster Omega Centauri is thought to be the surviving nucleus. The cluster’s metallicity—the abundance of elements heavier than hydrogen and helium—is very low, measured at [Fe/H] = –2.00 dex, meaning it has just 1/100th the iron abundance of the Sun.
The brightest stars in M56 are around 13th magnitude, and only about a dozen variable stars are known within it. These include V6, an RV Tauri star with a period of 90 days; V1, a Cepheid variable with a period of 1.510 days; V2, an irregular variable; and V3, a semiregular variable. In 2000, a faint diffuse X-ray emission was tentatively detected near the cluster, likely from interstellar medium heated by the cluster’s passage through the galactic halo. The cluster moves at a relative velocity of about 177 km/s, enough to heat the material in its wake to roughly 940,000 K. M56 is part of the Gaia Sausage, the hypothesized remains of a merged dwarf galaxy.
Quick Facts
- Epoch
- J2000
- Class
- X
- Constellation
- Lyra
- Ra
- 19 · 16 · 35.57
- Dec
- +30 · 11 · 00.5
- Dist Ly
- 32.9 kly
- Appmag V
- 8.3
- Radius Ly
- 42 ly
- Metal Fe
- –2.00
- Age
- 13.70 Gyr
- Names
- M56, NGC 6779, GCl 110, C 1914+300
Facts from the source article.
Lore & Background
Messier 56 was discovered by Charles Messier in 1779. It is located angularly about midway between Albireo (Beta Cygni) and Sulafat (Gamma Lyrae). Under a good night sky, it is tricky to find with large (50–80 mm) binoculars, appearing as a slightly fuzzy star, and can be resolved using a telescope with an aperture of 8 inches (20 cm) or larger. The cluster is about 32,900 light-years from Earth, measures roughly 84 light-years across, and contains 230,000 solar masses. It is about 31–32 kly from the Galactic Center and 4.8 kly above the galactic plane. Its estimated age is 13.70 billion years, and it follows a retrograde orbit through the Milky Way. The properties suggest it may have been acquired during the merger of a dwarf galaxy, of which Omega Centauri forms the surviving nucleus. Its metallicity is very low, [Fe/H] = –2.00 dex, which is 1/100 of the abundance in the Sun.
Reader's Guide
Messier 56's significance lies in its extreme properties and possible extragalactic origin. Its very low metallicity ([Fe/H] = –2.00 dex) indicates it formed early in the universe, and its retrograde orbit suggests it was not born in the Milky Way but captured from a dwarf galaxy. The cluster is part of the Gaia Sausage, the hypothesised remains of a merged dwarf galaxy. It contains only about a dozen known variable stars, including a RV Tauri star (V6, period 90 days), a Cepheid (V1, period 1.510 days), an irregular variable (V2), and a semiregular variable (V3). In 2000, a diffuse X-ray emission was tentatively identified from its vicinity, likely interstellar medium heated by the cluster's passage through the galactic halo at a relative velocity of about 177 km/s, heating the medium to 940,000 K. These features make M56 a key object for studying galaxy mergers and stellar populations.
Did You Know?
- Messier 56 has a metallicity of [Fe/H] = –2.00 dex, which is 1/100 of the Sun's abundance.
- It follows a retrograde orbit through the Milky Way, suggesting it was acquired from a dwarf galaxy merger.
- A diffuse X-ray emission was tentatively identified in 2000, likely from interstellar medium heated to 940,000 K by the cluster's motion.
More in Globular Clusters 1-24
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