Large Magellanic Cloud

The Large Magellanic Cloud (LMC) is a dwarf galaxy and satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (163,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (c. 16 kiloparsecs or 52,000 light-years away) and the possible dwarf irregular galaxy called the Canis Major Overdensity. It is about 9.86 kiloparsecs (32,200 light-years) across and has roughly one-hundredth the mass of the Milky Way, making it the fourth-largest galaxy in the Local Group after the Andromeda Galaxy (M31), the Milky Way, and the Triangulum Galaxy (M33). The LMC is classified as a Magellanic spiral. It contains a stellar bar that is geometrically off-center, suggesting that it was once a barred dwarf spiral galaxy before its spiral arms were disrupted, likely by tidal interactions from the nearby Small Magellanic Cloud (SMC) and the Milky Way's gravity. The LMC is predicted to merge with the Milky Way in approximately 2.4 billion years. With a declination of about −70°, the LMC is visible as a faint "cloud" from the Southern Hemisphere of the Earth and from as far north as 20° N. It straddles the constellations Dorado and Mensa and has an apparent length of about 10° to the naked eye, 20 times the Moon's diameter, from dark sites away from light pollution.

History of observation

Both the Large and Small Magellanic Clouds have been easily visible for southern nighttime observers well back into prehistory. It has been claimed that the first known written mention of the Large Magellanic Cloud was by the Persian astronomer 'Abd al-Rahman al-Sufi Shirazi (later known in Europe as "Azophi"), which he referred to as Al Bakr, the White Ox, in his Book of Fixed Stars around 964 AD. However, this seems to be a misunderstanding of a reference to some stars south of Canopus which he admits he had not seen. The first confirmed recorded observation was in a letter written in 1502 by Amerigo Vespucci after his second voyage. He mentioned "three Canopi [sic], two bright and one obscure"; "bright" refers to the two Magellanic Clouds, and "obscure" refers to the Coalsack.

Ferdinand Magellan sighted the LMC on his voyage in 1519 and his writings brought it into common Western knowledge. The galaxy now bears his name. The galaxy and southern end of Dorado are in the current epoch at opposition on about 5 December when thus visible from sunset to sunrise from equatorial points such as Ecuador, the Congos, Uganda, Kenya and Indonesia and for part of the night in nearby months. Above about 28° south, such as most of Australia and South Africa, the galaxy is always sufficiently above the horizon to be considered properly circumpolar, thus during spring and autumn the cloud is also visible much of the night, and the height of winter in June nearly coincides with closest proximity to the Sun's apparent position. Measurements with the Hubble Space Telescope, announced in 2006, suggest the Large and Small Magellanic Clouds may be moving too quickly to be orbiting the Milky Way. Astronomers discovered a new black hole inside the Large Magellanic Cloud in November 2021 using the European Southern Observatory's Very Large Telescope in Chile. Astronomers claim its gravity is influenced by a nearby star, which is about five times the mass of the Sun. In March 2025, the Center for Astrophysics announced strong evidence for a supermassive black hole in the Large Magellanic Cloud, the second-closest besides Sagittarius A*, with an estimated mass 600,000 times that of the Sun.

Geometry

The Large Magellanic Cloud has a prominent central bar and spiral arm. The central bar, with a radius of 6,900 light-years (2.13 kpc) and a position angle of about 121°, seems to be warped so that the east and west ends are nearer the Milky Way than the middle. In 2014, measurements from the Hubble Space Telescope made it possible to determine a rotation period of 250 million years. The LMC was long considered to be a planar galaxy that could be assumed to lie at a single distance from the Solar System. However, in 1986, Caldwell and Coulson found that field Cepheid variables in the northeast lie closer to the Milky Way than those in the southwest. From 2001 to 2002 this inclined geometry was confirmed by the same means, by core helium-burning red clump stars, and by the tip of the red giant branch. All three papers find an inclination of ~35°, where a face-on galaxy has an inclination of 0°. Further work on the structure of the LMC using the kinematics of carbon stars showed that the LMC's disk is both thick and flared, likely due to interactions with the SMC. Regarding the distribution of star clusters in the LMC, Schommer et al. measured velocities for ~80 clusters and found that the LMC's cluster system has kinematics consistent with the clusters moving in a disk-like distribution. These results were confirmed by Grocholski et al., who calculated distances to a sample of clusters and showed that the cluster system is distributed in the same plane as the field stars.

Distance

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