Large Magellanic Cloud

The Large Magellanic Cloud (LMC), also known as PGC 17223 and historically as Nubecula Major, is a barred Magellanic spiral galaxy (SB(s)m) and a satellite galaxy of the Milky Way. Located in the constellations of Dorado and Mensa at about 162,980 light-years (49,970 parsecs) away,   the Large Magellanic Cloud is the second-closest galaxy to us, after the Sagittarius Dwarf Spheroidal Galaxy (third-closest if including the disputed Canis Major Overdensity). Careful observations of stars indicate that the LMC is approximately 10 billion solar masses in mass. Being about 140,000 light-years in diameter, it is the fourth-largest object in the Local Group of galaxies, after the Andromeda Galaxy, the Milky Way, and the Triangulum Galaxy.

The LMC is one of few galaxies that can be seen with the naked eye. It is visible as a faint "cloud" and is only visible to the Earth's southern hemisphere. The galaxy is both in the constellations of Dorado and Mensa. Only visible in certain viewing conditions at places far away from light pollution, the galaxy has an apparent length of about 10° to the naked eye or about 20 times the Moon's diameter. It is one of two Magellanic Clouds, the other one being the Small Magellanic Cloud (SMC). The coordinates for this object in the night sky are 05h 23m 34.5s, −69° 45′ 22″.

The galaxy is predicted to collide with the Milky Way in about 2.4 billion years, which would smash gas clouds together and trigger star formation a little.

Observation
Since both of the Magellanic Clouds are easily visible, large and bright, southern nighttime observers can be traced well back into prehistory. The first possible mention of the Magellanic Clouds was by the Persian astronomer Abdul Rahman al-Sufi (عبدالرحمن الصوفی), also known as Azophi, in his book titled "Book of Fixed Stars" (كتاب صور الكواكب) around 964. He called it "Al-Bakr". However, it could be a misunderstanding of a reference to some stars south of Canopus which he had not seen. The first confirmed, recorded observation of the Magellanic Clouds was by the Italian merchant Amerigo Vespucci in a letter about his third voyage between 1503 to 1504. In his letter, he mentioned "three Canopes, two bright and one obscure". In this context, Amerigo's bright "Canopes" are thought to be the Magellanic Clouds, and "obscure" probably refers to the Coalsack Nebula.

In 1519, Ferdinand Magellan sighted the LMC on his discovery expedition and he recorded his sightings. His writings brought the LMC into common Western knowledge. The galaxy is now named after him, the Magellanic Clouds.

Size and mass
Based on the angular dimensions of 10.75° × 9.17° and the distance of about 162,980 ly, the size of the LMC is approximately 14,000 ly (4,292.42 pc). It is the larger of the two Magellanic Clouds.

By calculating the approximate number of stars in the LMC, the galaxy has a stellar mass of about 2.7 billion solar masses. In 2014, van der Marel and Kallivayalil published the results of the measurements of the LMC's mass and had given relatively modest estimates of 20 billion. However, wide-field surveys have revealed a wealth of debris in the outskirts of the LMC, indicating that the LMC may be significantly more massive. Several distinct lines of reasoning have suggested an LMC mass between 100 to 250 billion.

Movement
In 2006, measurements from the Hubble Space Telescope (HST) suggested that both Large and Small Magellanic Clouds may be moving too quickly to be orbiting the Milky Way. A few years later, in 2014, measurements from the Hubble Space Telescope determined that the LMC has a rotation period of 250 million years.

The LMC is predicted to collide with the Milky Way in approximately 2.4 billion years, which would smash huge gas clouds together and trigger star formation a little.

Distance
Distance to the LMC has been calculated using standard candles, such as Cepheid variables, which are among the most popular ways to calculate extragalactic distances. Other methods which can be used to calculate the distance to the LMC are eclipsing binaries and the light echoes of supernova 1987A. These are geometric measurements, without any stellar models, mass, or compositional assumptions.

In 2006, the Cepheid luminosity was revised using Cepheid variables in the galaxy Messier 106, covering a range of stellar metallicities. Using this improved calibration, astronomers found the LMC's distance modulus of 18.41 or 160,000 ly (48,000 pc). Other authors have also confirmed this distance.

In March 2013, a study using late-type eclipsing binaries to determine the distance more accurately was published in the scientific journal Nature. Pietrzyński et al. obtained a distance of 49,970 pc (about 162,980 light-years) with an accuracy of 2.2%.

Morphology
The LMC is a barred Magellanic spiral. The galaxy is classified as an SB(s)m galaxy in the de Vaucouleurs–Sandage extended classification system of spiral galaxies. It is also classified as an irregular galaxy due to its chaotic appearance and warped shape.

Tidal interaction between the LMC and the Milky Way during the last 9 billion years has transformed the initially thin, unbarred LMC disk into a thick, barred disk with a hot stellar halo. The off-center stellar bar indicates that it was probably once a barred spiral galaxy before the Milky Way disrupted its spiral arms again. The central bar appears to be warped, and the east and west ends are closer to the Milky Way than the middle part. The shape of the LMC was long thought to be fully face-on, and the entire galaxy could be assumed to lie at a single distance from the Solar System. However, in 1986, Caldwell and Coulson discovered that Cepheid variable stars in the northeast portion of the galaxy are nearer the Milky Way than those in the southwest. From 2001 to 2002, other authors confirmed this inclined geometry. All observations found that the galaxy is inclined by about 35°, which is in contrast to a face-on galaxy which would have an inclination of 0°. Using the kinematics of carbon stars, van der Marel et al. concluded that the LMC's disk is both thick and flared. The distribution of star clusters in the galaxy appears to lie on a single plane, though, as Schommer et al. measured. They measured velocities for about 80 star clusters and found that the LMC's cluster system has motions consistent with the clusters moving in a disk-like distribution. These results were later 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.

Deep-sky objects
Like many irregular and spiral galaxies, the LMC is rich in gas and dust and is currently undergoing a lot of star formation activity. It also contains some of the most active and the largest star-forming regions and H II gas clouds in the Local Group, such as the Tarantula Nebula (30 Doradus), N11, and NGC 2020. Besides containing a lot of star-forming regions, the LMC also contains a considerable number of globular clusters, open clusters, and planetary nebulae, so much so that Robert Burnham Jr. once said that the LMC is an "astronomical treasure-house, a great celestial laboratory for the study of the growth and evolution of the stars". Through galaxy surveys, astronomers have found about 60 globular clusters, 400 planetary nebulae, and 700 open clusters, along with hundreds of thousands of giant and supergiant stars like R136a1. The closest known supernova also occurred in the LMC—the SN 1987A.

Between the LMC and the SMC is a bridge of neutral hydrogen gas named the Magellanic Bridge (MBR), which connects the two galaxies together. The existence of the bridge reveals tidal interactions between the two. It is a star-forming region, though not as active as those in the LMC. Other than the MBR, there is also the Magellanic Stream, a stream of high-velocity clouds of gas extending from the Magellanic Clouds over the Galactic south pole of the Milky Way.

X-ray sources
On September 20, 1966, the Nike-Tomahawk rocket was launched from the Johnston Atoll in the USA, and it didn't detect any X-rays from either of the Magellanic Cloud. The LMC was not detected in the X-ray range of 8–80 kilo-electronvolts (keV). Another rocket was also launched from the same atoll on October 29, 1968, and scanned the LMC for X-rays. This time, it detected a discrete X-ray source in the LMC, and it was the LMC itself. The X-ray source extended over about 12° and is consistent with the LMC (about 11°). The emission rate of X-ray between the 1.5–10.5 keV range for a distance of 163,000 ly (50,000 pc) is 4 × 1038 ergs/s. On September 24, 1970, on the same atoll, the Thor ballistic missile was launched to altitudes above 300 km to extend observations of the LMC. This time, the X-ray source appeared extended by a few arcmins, and now the star Epsilon Doradus (it is a foreground star; not related to the LMC) is contained within the border of the X-ray source. The X-ray emission rate over the range 1.5–10.5 keV was 6 × 1038 ergs/s.

The first discovered X-ray source within the galaxy itself is the LMC X-1, a high-mass X-ray binary star system. Other luminous X-ray binaries in the galaxy are LMC X-2, X-3, X-4, and A 0538–66. Other than X-ray binaries, supernova remnants are also sometimes X-ray sources. For example, the DEM L316 is a complex of two supernova remnants and is the result of Type Ia and Type II supernova. Besides that, pulsars also give off X-rays. For instance, SNR 0538-69.1, a 16 ms X-ray pulsar.

Redshifts
The tables below contain quantities derived by the preferred redshift ($$z$$) of 0.00093 with the Hubble's constant ($$H_0$$) of 67.8 km/sec/Mpc, density ($$\Omega$$) of matter being 0.308 and density of vacuum being 0.692.

SED plot
The following is graph that shows the SED (spectral energy distribution) plot for LMC:

Formation
The LMC is thought to have formed about the same time as the Milky Way, about 13.6 billion years ago or 200 million years after the Big Bang. It was probably initially formed as a thin, unbarred spiral galaxy before tidal interactions with the Milky Way during the last 9 billion years caused its structure to be warped into a thick, barred spiral galaxy. The interaction also gave the LMC a hot stellar halo. More tidal interactions with the Milky Way caused the galaxy's spiral arms to morph into the familiar shape that we see today.

According to a paper published in 2021 by Mazzi et al., the most intense period of star formation happened between about 4 and 0.5 billion years ago, when dust and gas in the LMC turned into stars at rates of about 0.3 times the mass of the sun per year. Although the researchers’ conclusions matched with previous works, they found that the star formation rates were lower when the galaxy was still young. This discovery is essential in understanding the formation of stars more profoundly and their formation in the Local Group.

From Earth
The LMC is only visible in the Southern Hemisphere of the Earth. They’re not visible north of about 17° north latitude. Anyone in the Southern Hemisphere can see the LMC any night of the year because they’re south circumpolar. In other words, they’re close enough to the South Celestial Pole that they never set.

The LMC is easier to spot than the SMC, but they both require dark skies far away from light pollution. The LMC shines at magnitude 0.13. A star of that magnitude would appear very bright because of its pinpoint source of light, but for the galaxy, its diffuse, spread-out light means it appears as a hazy smudge on the sky like a cloud.

Surrounding sky
The picture below is an image of the sky surrounding the LMC, taken from the Aladin Sky Atlas.