Messier 56
A globular cluster in Lyra with a possible dwarf galaxy origin.
Messier 56, cataloged as M56 or NGC 6779, is a globular cluster located in the constellation Lyra. Charles Messier first spotted it in 1779. In the sky, it sits roughly halfway between the stars Albireo (Beta Cygni) and Sulafat (Gamma Lyrae). Under good conditions, it’s a challenge to pick out with large binoculars (50–80 mm), appearing as a slightly hazy star; a telescope with an aperture of at least 8 inches (20 cm) is needed to resolve individual stars.
The cluster lies about 32,900 light-years from Earth and spans roughly 84 light-years across, with a mass of 230,000 times that of the Sun. It’s located around 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 Milky Way’s plane. Estimated to be 13.70 billion years old, M56 follows a retrograde orbit around the galaxy. Its properties hint that it might have been captured when the Milky Way merged with a dwarf galaxy—the same event that left Omega Centauri as the surviving nucleus.
M56 has a very low metallicity, meaning it contains only about 1/100th the abundance of elements heavier than hydrogen and helium found in the Sun, measured at [Fe/H] = –2.00 dex. Its brightest stars shine at 13th magnitude, and it hosts only about a dozen known variable stars, including V6 (an RV Tauri star with a 90-day period), V1 (a Cepheid with a 1.510-day period), V2 (irregular), and V3 (semiregular). In 2000, a faint X-ray emission was tentatively detected near the cluster, likely from interstellar medium heated as the cluster moves through the galactic halo at a relative speed of about 177 km/s, raising the temperature in its wake to roughly 940,000 K.
M56 is considered part of the Gaia Sausage, the hypothesized remains of a merged dwarf galaxy.
- Discovered by
- Charles Messier
- Discovery year
- 1779
- Distance from earth
- 32,900 light-years
- Diameter
- 84 light-years
- Mass
- 230,000 solar masses
- Age
- 13.70 billion years
- Metallicity
- [Fe/H] = –2.00 dex (1/100 of solar abundance)
Lore & Background
Messier 56 was discovered by Charles Messier in 1779. It is angularly found about midway between Albireo (Beta Cygni) and Sulafat (Gamma Lyrae). In a good night sky it is tricky to find with large (50–80 mm) binoculars, appearing as a slightly fuzzy star. The cluster can be resolved using a telescope with an aperture of 8 inches (20 cm) or larger.
M56 is about 32,900 light-years away from Earth and measures roughly 84 light-years across, containing 230,000 solar masses. It is about 31–32 kly from the Galactic Center and 4.8 kly above the galactic plane. 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 a dwarf galaxy, of which Omega Centauri forms the surviving nucleus. Its metallicity is very low at [Fe/H] = –2.00 dex, which is 1/100 of the abundance in the Sun.
The brightest stars in M56 are of 13th magnitude, while it contains only about a dozen known variable stars, such as V6 (RV Tauri star; period: 90 days) or V1 (Cepheid: 1.510 days); 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, most likely interstellar medium heated by the passage of the cluster through the galactic halo. The relative velocity of the cluster is about 177 km/s, sufficient to heat the medium in its wake to a temperature of 940,000 K. M56 is part of the Gaia Sausage, the hypothesised remains of a merged dwarf galaxy.
Reader's Guide
Messier 56 is significant as a globular cluster whose properties—low metallicity, retrograde orbit, and membership in the Gaia Sausage—suggest it was not born in the Milky Way but was acquired during the merger of a dwarf galaxy. This makes it a key object for studying galactic cannibalism and the assembly history of the Milky Way. Its very low metallicity ([Fe/H] = –2.00 dex) indicates it is extremely old and metal-poor, consistent with its estimated age of 13.70 billion years. The cluster's retrograde orbit and its association with the Gaia Sausage, the hypothesised remains of a merged dwarf galaxy, provide evidence for past galactic mergers. The tentative detection of diffuse X-ray emission in 2000, likely from heated interstellar medium in its wake, adds to its interest as a dynamic object moving through the galactic halo. For amateur observers, M56 is a challenging target, appearing as a fuzzy star in large binoculars and requiring an 8-inch telescope to resolve individual stars. Its location midway between Albireo and Sulafat aids in locating it.
Did You Know?
- It has a very low metallicity of [Fe/H] = –2.00 dex, which is 1/100 of the Sun's abundance.
- The cluster follows a retrograde orbit through the Milky Way and is part of the Gaia Sausage.
- A diffuse X-ray emission was tentatively identified from its vicinity in 2000, likely from heated interstellar medium.
Frequently Asked Questions
What is Messier 56?
Messier 56 (also listed as NGC 6779) is a globular cluster located in the constellation Lyra. Charles Messier first recorded it in 1779, and it is estimated to be around 13.7 billion years old.
Where in the sky can I find Messier 56?
M56 sits roughly halfway between Albireo in Cygnus and Sulafat in Lyra. Under dark skies it shows up as a faint, slightly hazy star-like smudge.
How far away is Messier 56 and how big is it?
The cluster is about 32,900 light-years from Earth and spans roughly 84 light-years across. Its total mass works out to approximately 230,000 solar masses.
Can I see Messier 56 with binoculars?
Large binoculars in the 50–80 mm range can pick it out as a dim, fuzzy point under good conditions, but it remains a tough target. Resolving individual member stars calls for a telescope with at least an 8-inch (20 cm) aperture.
What is interesting about Messier 56's origin?
M56 is thought to have a possible dwarf-galaxy origin, meaning it may have formed from or been associated with a smaller galaxy rather than arising purely from the Milky Way's own material. That makes it a useful object for studying early galactic evolution.
More in Messier Objects, Part 2 1-24
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