Messier 54 (M54) is an extragalactic globular cluster located in the southern constellation Sagittarius. It has an apparent magnitude of 8.37 and lies at a distance of 87,400 light years from Earth. It has the designation NGC 6715 in the New General Catalogue.
The cluster is very easy to find as it lies near Ascella, Zeta Sagittarii, the third brightest star in Sagittarius and one of the stars that form the celestial Teapot. M54 is positioned 0.5 degrees south and 1.5 degrees west of the star. GoStargazing
While M54 is easy to locate, even large amateur telescopes cannot resolve it into individual stars, and binoculars and small telescopes reveal only a round, hazy patch of light. The best time of year to observe the cluster is during the months of June, July and August, but it never rises high above horizon for northern observers.
Messier 54 was the first globular cluster discovered to belong to a different galaxy. It was originally thought to lie at a distance of 50,000 to 65,000 light years from the solar system and be one of the many globulars within the Milky Way. However, in 1994 scientists discovered that M54 most likely belonged to the Sagittarius Dwarf Elliptical Galaxy (SagDEG), one of the satellite galaxies of the Milky Way that will eventually be captured and eaten by our galaxy. Even though it wasn’t recognised as one for 200 years, M54 is considered to be the first extragalactic cluster ever discovered.The estimated age of M54 is 13 billion years. The cluster is moving away from us at about 142 km/s, which is a similar velocity to that of the Sagittarius Dwarf Elliptical Galaxy (130 km/s). The galaxy also lies at a similar distance (80,000 to 90,000 light years).
The cluster is positioned in the centre of the galaxy, which led some to speculate that it may in fact be the galaxy’s core. Others, however, argued that M54 was a real globular cluster and that it was the decay of its orbit that caused the cluster to fall to the galaxy’s central region. The decay of the cluster’s orbit is thought to have been caused by dynamical friction, or gravitational drag, which occurs when a moving body loses momentum and kinetic energy as a result of gravitational interactions with other objects in space.
Messier 54 can be seen in the vicinity of two other bright globular clusters, Messier 69 and Messier 70. It is, however, roughly three times as distant. GoStargazing
In 2009, astronomers discovered evidence of an intermediate-mass black hole in the centre of the cluster. It was the first object of its kind ever detected in a globular cluster. The black hole has an estimated mass of 9,400 solar masses.
Messier 54 was discovered by Charles Messier on July 24, 1778. Messier included the object in his catalogue with the following description: “Very faint nebula, discovered in Sagittarius; its center is brilliant & it contains no star, seen with an achromatic telescope of 3.5 feet [FL]. Its position has been determined from Zeta Sagittarii, of 3rd magnitude.Image Credit ESA/Hubble & NASA
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