The Large Magellanic Cloud

The Large Magellanic Cloud (LMC) is a dwarf irregular galaxy located on the border between the constellations Dorado and Mensa.

The galaxy is believed to be a satellite of the Milky Way and a member of the Local Group of galaxies, which includes about 30 galaxies that are loosely bound together by their gravitation.

The Large Magellanic cloud lies an an approximate distance of 163,000 light years, or just under 50 kiloparsecs from Earth. Covering several degrees of the sky, the Large Magellanic Cloud is quite large in size, as its name indicates, and easy to find without binoculars for observers in the southern hemisphere.

It is the fourth largest galaxy in the Local Group, after Andromeda Galaxy, the Milky Way, and Triangulum Galaxy. The LMC is also one of very few galaxies that are visible to the naked eye.

The galaxy appears as a faint cloud more than 20 times the width of the full Moon. The visible part of the Large Magellanic Cloud is about 17,000 light years across.

Along with the Small Magellanic Cloud (SMC), the LMC appears like a piece of the Milky Way that has broken off, when in fact both Magellanic Clouds are separate small galaxies.

Both Magellanic Clouds are companions to our galaxy. The Large Magellanic Cloud is orbiting the Milky Way and is gravitationally bound to it. It is the third nearest galaxy to the Milky Way, with only the Sagittarius Dwarf Spheroidal galaxy in Sagittarius constellation  and the Canis Major Dwarf Galaxy in Canis Major lying closer, at 16 and 12.9 kiloparsecs, respectively. (The status of the Canis Major Dwarf as a galaxy is under dispute.)

The Large Magellanic Cloud is often listed as an irregular type galaxy because of its appearance, which is likely the result of the galaxy’s tidal interactions with the Milky Way and the Small Magellanic Cloud (SMC), located in Tucana constellation. The LMC has a prominent bar in its central region, which indicates that it may have previously been a barred spiral galaxy.

The Magellanic Clouds are connected by a bridge of gas, which is a region of active star formation between the two galaxies. The bridge indicates that the Magellanic Clouds are tidally interacting. The galaxies also have have a common envelope of neutral hydrogen, which means that they have been gravitationally bound to each other for a very long time. The Small Magellanic Cloud is more distant from us, lying at a distance of about 200,000 light years from Earth.

The Large Magellanic Cloud (14,000 light years across) has twice the diameter of the Small Magellanic Cloud (7,000 light years), but is signficantly smaller than the Milky Way (100,000 light years).

Finding the Large Magellanic Cloud is not difficult for observers in the southern hemisphere. For those living below latitude 20°S, the galaxy is circumpolar, which means that it can be seen every night throughout the year if the sky is clear. The LMC is located about 22 degrees from the South Celestial Pole and stretches across an area approximately 9 by 11 degrees on the border between Dorado and Mensa.

The easiest way to find the galaxy is by drawing an imaginary line from Sirius past the right side of Canopus and follow the line to the LMC.

In northern latitudes, the Large Magellanic Cloud can be seen south of latitude 20°N. The galaxy is not easy to observe because even when it does appear above the southern horizon, it only appears very low in the sky. The LMC is best seen in the evenings from December to April, when the constellation Orion also reaches its highest point in the sky.

FACTS

The Large Magellanic Cloud has a mass roughly 10 billion times that of the Sun, which makes the galaxy a hundred times less massive than the Milky Way.

The LMC has an estimated rotation rate of 250 million years. Astronomers calculated this by tracking the motion of the stars within the galaxy sideways with respect to the plane of the sky. This was the first time this type of measuring was used for a galaxy.

With a diameter spanning approximately 14,000 light years, the LMC is the fourth largest galaxy in the Local Group, smaller in size only than the Andromeda Galaxy  (Messier 31), the Milky Way, and the Triangulum Galaxy (Messier 33).

A hypothetical observer looking at the Milky Way from a planet within the Large Magellanic Cloud would be treated to quite a spectacle. With an apparent magnitude of -2.0, the Milky Way would appear more than 14 times brighter than the LMC appears to us, and would span roughly 36° of the sky, which is more than 70 full Moons in width.

The Large Magellanic Cloud was considered to be the nearest external galaxy to our own until 1994, when astronomers discovered the Sagittarius Dwarf Elliptical Galaxy, which is only 80,000 light years distant.

The Magellanic Clouds have both been greatly distorted as a result of tidal interaction with our galaxy, the Milky Way. The three galaxies are connected by streams of neutral hydrogen. The gravity of the Magellanic Clouds has affected the Milky Way, too, distorting the outer regions of our galaxy’s disk.

The LMC is often classified as a Magellanic-type dwarf spiral galaxy because it has a central bar and a spiral arm, but it is sometimes considered an irregular galaxy because of its unusual shape. The galaxy’s central bar appears warped, with its east and west ends closer to the Milky Way than the middle. The galaxy is inclined at 35°. (A galaxy appearing face-on to an observer on Earth would have an inclination of 0°.) The Small Magellanic Cloud, also an irregular dwarf galaxy, shows signs of a bar structure, too, and is also frequently reclassified as a Magellanic spiral.

The Large and Small Magellanic Clouds are separated by about 21° in the sky. The real distance between the galaxies is approximately 75,000 light years.

The estimated number of stars in the Large Magellanic Cloud is 10 billion, which is roughly a tenth of the Milky Way’s mass.

The Magellanic Clouds were formed roughly at the same time as our galaxy, some 13 billion years ago. The galaxies are believed to have originally formed as barred spirals.

They are currently drawn by the larger Milky Way into its orbit and distorted by the gravitational interactions. What is unusual about these two galaxies is that, unlike most satellites, which are stripped of gas by their larger neighbours, the Magellanic Clouds still appear quite radiant, with enough gas to keep forming new stars.

Astronomers have suggested that the two small galaxies have been spared the effect of the tidal encounter because they are speeding past the Milky Way at an unusually high speed, not really giving the larger galaxy a chance to strip them of their gas supply.

They are thought by some to only have come so close to the Milky Way some 200 million years ago, and that our galaxy has not really affected them as much as previously thought.

Furthermore, recent studies indicate that the Magellanic Clouds have been periodically approaching each other every few billion years and that the starburst activity was sparked by a collision between them. The larger galaxy is believed to have drawn millions of stars from the smaller one.

The Milky Way will probably eventually consume the Magellanic Clouds, but it is difficult to predict when. The two galaxies closer to us than the Magellanic Clouds will likely collide with the Milky Way first.
In spite of being relatively small in size for a galaxy, the Large Magellanic Cloud contains a number of notable deep sky objects.

These include globular and open clusters, planetary nebulae, and diffuse nebulae. The galaxy contains roughly 400 planetary nebulae, 60 globular clusters, and 700 open clusters.

The most famous nebula found in the galaxy is the Tarantula Nebula (NGC 2070), the most active starburst region in the Local Group of galaxies.

The nebula spans about 700 light years and, if it were as close to us as the Orion Nebula, the Tarantula would appear 55 times larger than the full Moon in the sky.

Another notable star-forming region in the LMC is LHA 120-N 11.

The Large Magellanic Cloud was the site of the nearest observed supernova since the invention of the telescope.

First detected on February 24, 1987, SN 1987A was the brightest supernova seen from Earth in over four centuries. It was classified as a peculiar Type II supernova and was one of the most interesting deep sky objects for astronomers and astrophysicists to observe in the late 20th century.

A supernova remnant, SNR N86, also known as the Lionel-Murphy SNR, is a nitrogen-abundant remnant, also found in the Large Magellanic Cloud. The object was named after Australian High Court Justice Lionel Murphy, to acknowledge his interest in science and because it resembled a cartoonist’s drawing of his nose.

One of the clusters in the Large Magellanic Cloud contains R136a1, currently the most massive and most luminous star known. R136a1 has a mass 265 times that of the Sun and a luminosity of 8,700,000 Suns. The star belongs to the super star cluster R136, located near the Tarantula Nebula.

Mythology

The Large Magellanic Cloud is too far south to be associated with any classical northern myths, but has considerable cultural significance in countries in the southern hemisphere.

next to the constellation Mensa, which was named after the Table Mountain in South Africa. (Mensa means “table” in Latin.) In South Africa, the LMC is associated with a puff of smoke from a pipe-smoking contest held on the mountain.

In Australian Aboriginal culture, the Large Magellanic Cloud represents the campsite of an old man, while his wife’s campsite is represented by the Small Magellanic Cloud.

The couple, known by the joint name of Jukara, were said to be too old to feed themselves, so other star beings would bring them fish from the celestial river represented by the Milky Way.

History

The first known mention of the LMC was by the Persian astronomer Al Sufi In his Book of Fixed Stars (964 AD). Al Sufi called the object al-Bakr, which means “the sheep,” in a phrase meaning “the sheep of the southern Arabs.” He mentioned that the LMC could not be seen from Baghdad and northern Arabia, but is visible from Arabia’s southernmost point, the strait of Bab el Mandeb (latitude 12°15′ N).
The first Europeans to observe the Magellanic Clouds were Italian explorers Peter Martyr d’Anghiera and Andrea Corsali in the late 15th century. Antonio Pigafetta, who went on Ferdinand Magellan’s expedition to circumnavigate the world from 1519 to 1522 also noted the objects.

The Portuguese navigator Ferdinand Magellan was the one responsible for bringing the Large Magellanic Cloud into common western knowledge, which is why the galaxy was later named after him. The LMC is mentioned in his writings describing his voyage in 1519. Magellan died during that expedition in the Philippines, but his crew brought the documentation of the discovery back home to Europe.

The two galaxies, however, did not get named after Magellan until much later. Johann Bayer called the galaxies Nubecula Major and Nubecula Minor in his Uranometria (1603), and the French astronomer Lacaille called them le Grand Nuage and le Petit Nuage, meaning “the large cloud” and “the small cloud.”

Amerigo Vespucci mentioned the object in a letter about his third voyage, around 1503-4. In the letter, he describes “three Canopes, two bright and one obscure.” The “obscure” referred to the Coalsack Nebula in the southern constellation Crux and the “bright” to the Magellanic Clouds.

The American astronomer Edwin Hubble was the one to establish the extragalactic nature of the galaxies, which made it clear that the Magellanic Clouds were separate objects.

Large Magellanic Cloud
Constellation: Dorado/Mensa
Type: SB(s)m
Coordinates: 05h 23m 34.5s (right ascension), -69°45’22” (declination)
Distance: 162,980 light years (49.97 kiloparsecs)
Apparent magnitude: 0.9
Apparent dimensions: 10.75° × 9.17°
Diameter: 14,000 light years
Designations: Large Magellanic Cloud, LMC, ESO 56- G 115, PGC 17223, Nubecula Major