The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way. At a distance of about 50 kiloparsecs (≈163,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (~16 kpc) and the possible dwarf irregular galaxy known as the Canis Major Overdensity. Based on readily visible stars and a mass of approximately 10 billion solar masses, the diameter of the LMC is about 14,000 light-years (4.3 kpc), making it roughly one one-hundredth as massive as the Milky Way. This makes the LMC 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 a barred dwarf spiral galaxy before its spiral arms were disrupted, likely by tidal interactions from the Small Magellanic Cloud (SMC), and the Milky Way's gravity.
With a declination of about -70°, the LMC is visible as a faint "cloud" only in the southern celestial hemisphere and from latitudes south of 20° N, straddling the border between the constellations of Dorado and Mensa, and appears longer than 20 times the Moon's diameter (about 10° across) from dark sites away from light pollution.
The Milky Way and the LMC are expected to collide in approximately 2.4 billion years.
|Large Magellanic Cloud|
The Large Magellanic Cloud
|Observation data (J2000 epoch)|
|Right ascension||05h 23m 34.5s|
|Declination||−69° 45′ 22″|
|Distance||163.0 kly (49.97 kpc)|
|Apparent magnitude (V)||0.9|
|Size||14,000 ly in diameter|
|Apparent size (V)||10.75° × 9.17°|
|LMC, ESO 56- G 115, PGC 17223, Nubecula Major|
Although both clouds have been easily visible for southern nighttime observers well back into prehistory, 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"), in his Book of Fixed Stars around 964 AD.
The next recorded observation was in 1503–4 by Amerigo Vespucci in a letter about his third voyage. In this letter he mentions "three Canopes [sic], two bright and one obscure"; "bright" refers to the two Magellanic Clouds, and "obscure" refers to the Coalsack.
The Large Magellanic Cloud has a prominent central bar and a spiral arm. The central bar 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 that the LMC has 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 portion of the LMC lie closer to the Milky Way than Cepheids in the southwest portion. More recently, this inclined geometry for field stars in the LMC has been confirmed via observations of Cepheids, core helium-burning red clump stars and the tip of the red giant branch. All three of these 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. 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 number of clusters and showed that the LMC's cluster system is in fact distributed in the same plane as the field stars.
The distance to the LMC has been calculated using a variety of standard candles, with Cepheid variables being one of the most popular. Cepheids have been shown to have a relationship between their absolute luminosity and the period over which their brightness varies. However, Cepheids appear to suffer from a metallicity effect, where Cepheids of different metallicities have different period–luminosity relations. Unfortunately, the Cepheids in the Milky Way typically used to calibrate the period–luminosity relation are more metal rich than those found in the LMC.
Modern 8-meter-class optical telescopes have discovered eclipsing binaries throughout the Local Group. Parameters of these systems can be measured without mass or compositional assumptions. The light echoes of supernova 1987A are also geometric measurements, without any stellar models or assumptions.
In 2006, the Cepheid absolute luminosity was re-calibrated using Cepheid variables in the galaxy Messier 106 that cover a range of metallicities. Using this improved calibration, they find an absolute distance modulus of 18.41, or 48 kpc (~157,000 light-years). This distance has been confirmed by other authors.
By cross-correlating different measurement methods, one can bound the distance; the residual errors are now less than the estimated size parameters of the LMC.
The results of a study using late-type eclipsing binaries to determine the distance more accurately was published in the scientific journal Nature in March 2013. A distance of 49.97 kpc (163,000 light-years) with an accuracy of 2.2% was obtained.
Like many irregular galaxies, the LMC is rich in gas and dust, and it is currently undergoing vigorous star formation activity. It is home to the Tarantula Nebula, the most active star-forming region in the Local Group.
The LMC has a wide range of galactic objects and phenomena that make it aptly known as an "astronomical treasure-house, a great celestial laboratory for the study of the growth and evolution of the stars," as described by Robert Burnham Jr. Surveys of the galaxy have found roughly 60 globular clusters, 400 planetary nebulae, and 700 open clusters, along with hundreds of thousands of giant and supergiant stars. Supernova 1987a—the nearest supernova in recent years—was also located in the Large Magellanic Cloud. The Lionel-Murphy SNR (N86) nitrogen-abundant supernova remnant was named by astronomers at the Australian National University's Mount Stromlo Observatory, in acknowledgement of Australian High Court Justice Lionel Murphy's interest in science and because of SNR N86's perceived resemblance to his large nose.
There is a bridge of gas connecting the Small Magellanic Cloud (SMC) with the LMC, which is evidence of tidal interaction between the galaxies. The Magellanic Clouds have a common envelope of neutral hydrogen indicating they have been gravitationally bound for a long time. This bridge of gas is a star-forming site.
No X-rays above background were observed from the Magellanic Clouds during the September 20, 1966, Nike-Tomahawk flight. A second Nike-Tomahawk rocket was launched from Johnston Atoll on September 22, 1966, at 17:13 UTC and reached an apogee of 160 km (99 mi), with spin-stabilization at 5.6 rps. The LMC was not detected in the X-ray range 8–80 keV.
Another Nike-Tomahawk was launched from Johnston Atoll at 11:32 UTC on October 29, 1968, to scan the LMC for X-rays. The first discrete X-ray source in Dorado was at RA 05h 20m Dec −69°, and it was the Large Magellanic Cloud. This X-ray source extended over about 12° and is consistent with the Cloud. Its emission rate between 1.5–10.5 keV for a distance of 50 kpc is 4 x 1038 ergs/s. An X-ray astronomy instrument was carried aboard a Thor missile launched from Johnston Atoll on September 24, 1970, at 12:54 UTC and altitudes above 300 km (186 mi), to search for the Small Magellanic Cloud and to extend previous observations of the LMC. The source in the LMC appeared extended and contained the star ε Dor. The X-ray luminosity (Lx) over the range 1.5–12 keV was 6 × 1031 W (6 × 1038 erg/s).
The Large Magellanic Cloud (LMC) appears in the constellations Mensa and Dorado. LMC X-1 (the first X-ray source in the LMC) is at RA 05h 40m 05s Dec −69° 45′ 51″, and is a high mass X-ray binary source (HMXB). Of the first five luminous LMC X-ray binaries: LMC X-1, X-2, X-3, X-4, and A 0538–66 (detected by Ariel 5 at A 0538–66); LMC X-2 is the only one that is a bright low-mass X-ray binary system (LMXB) in the LMC.
DEM L316 in the Large Magellanic Cloud consists of two supernova remnants. Chandra X-ray spectra show that the hot gas shell on the upper left contains a high abundance of iron. This implies that the upper-left SNR is the product of a Type Ia supernova. The much lower iron abundance in the lower SNR indicates a Type II supernova.
Barred irregular galaxy
A barred irregular galaxy is an irregular version of a barred spiral galaxy. Examples include the Large Magellanic Cloud and NGC 6822. Some barred irregular galaxies (like the Large Magellanic Cloud) may be dwarf spiral galaxies, which have been distorted into an irregular shape by tidal interactions with a more massive neighbor.List of largest stars
Below is an ordered list of the largest stars currently known by radius. The unit of measurement used is the radius of the Sun (approximately 695,700 km; 432,288 mi).
The exact order of this list is very incomplete, as great uncertainties currently remain, especially when deriving various important parameters used in calculations, such as stellar luminosity and effective temperature. Often stellar radii can only be expressed as an average or within a large range of values. Values for stellar radii vary significantly in sources and throughout the literature, mostly as the boundary of the very tenuous atmosphere (opacity) greatly differs depending on the wavelength of light in which the star is observed.
Radii of several stars can be directly obtained by stellar interferometry. Other methods can use lunar occultations or from eclipsing binaries, which can be used to test other indirect methods of finding true stellar size. Only a few useful supergiant stars can be occulted by the Moon, including Antares and Aldebaran. Examples of eclipsing binaries include Epsilon Aurigae, VV Cephei, and HR 5171.NGC 1712
NGC 1712, also known as GC 942, JH 2685, and Dunlop 112 is an open cluster in the constellation of Dorado. It is relatively small, and is located inside the Large Magellanic Cloud. NGC 1712 was originally discovered in 1826 by James Dunlop, although Herschel rediscovered it in 1834. Nine variable stars have been discovered in it so far, with three suspected to be binary systems.NGC 1783
NGC 1783 (also known as ESO 85-SC29) is a globular cluster within the Dorado constellation and part of the Large Magellanic Cloud, a satellite dwarf galaxy of the Milky Way. It is one of the brightest globular clusters in the LMC as viewed from Earth. It was discovered in 1835 by John Herschel. The compiler of the New General Catalogue, John Louis Emil Dreyer, described this cluster as "considerably bright, large, round, very gradually pretty much brighter middle, mottled but not resolved."NGC 1818
NGC 1818 is a young globular cluster in the Large Magellanic Cloud. It was discovered by astronomer James Dunlop in 1826.NGC 1847
NGC 1847 is a young, massive star cluster in the bar of the Large Magellanic Cloud in the constellation Dorado. It was discovered in 1835 by John Herschel with an 18.7-inch reflecting telescope.NGC 1850
NGC 1850 is a double cluster and a super star cluster in the Dorado constellation, located in the Large Magellanic Cloud at the distance of 168,000 ly (51,510 pc). It was discovered by James Dunlop in 1826. It is an unusual cluster of stars because the distribution of its stars is like a globular cluster, but unlike the globular clusters of the Milky Way it is composed of young stars. The only similar object in the Milky Way is Westerlund 1.NGC 1852
NGC 1852 is a star cluster in the Large Magellanic Cloud in the constellation Dorado. It was discovered in 1826 by James Dunlop with a 9-inch reflecting telescope.NGC 1860
NGC 1860 is an open cluster in the Large Magellanic Cloud in the constellation Dorado. It was discovered in 1836 by John Herschel with an 18.7-inch reflecting telescope.NGC 1868
NGC 1868 is a globular cluster in the Large Magellanic Cloud in the constellation Dorado. It was discovered by John Herschel in 1834.NGC 1872
NGC 1872 is an open cluster within the Large Magellanic Cloud in the constellation Dorado. It was discovered by James Dunlop in 1826.NGC 1872 has characteristics of both globular clusters and open clusters - it is visually as rich as a typical globular but is much younger, and, like many open clusters, has bluer stars. Such intermediate clusters are common in the Large Magellanic Cloud.NGC 1903
NGC 1903 is a star cluster in the Large Magellanic Cloud in the constellation Dorado. It was discovered in 1834 by John Herschel with an 18.7-inch reflecting telescope.NGC 1935
NGC 1935 (also known as ESO 56-EN110 and IC 2126) is an emission nebula which is part of the larger LMC-N44 nebula in the Dorado constellation. NGC 1935 is also located in the Large Magellanic Cloud. It was discovered by John Herschel in 1834 which was added to the Catalogue of Nebulae and Clusters of Stars as NGC 1935 and was observed by Williamina Fleming in 1901 and was later added to the Index Catalogue as IC 2126.NGC 1969
NGC 1969 (also known as ESO 56-SC124) is an open star cluster in the Dorado constellation and is part of the Large Magellanic Cloud. It was discovered by James Dunlop on September 24, 1826. Its apparent size is 0.8 arc minutes.NGC 1994
NGC 1994 (also known as ESO 56-SC136) is an open cluster in the Dorado constellation which is located in the Large Magellanic Cloud. It was discovered by John Herschel on 16 December 1835. It has an apparent magnitude is 9.8 and its size is 0.60 arc minutes.NGC 1997
NGC 1997 (also known as ESO 86-SC1) is an open cluster located in the Dorado constellation which is part of the Large Magellanic Cloud. It was discovered by John Herschel on November 30, 1834. Its apparent magnitude is 13.43 and its size is 1.80 arc minutes.NGC 2027
NGC 2027 (also known as ESO 86-SC13) is a 12th magnitude open cluster located in the Dorado constellation which is also part of the Large Magellanic Cloud and was discovered by James Dunlop on November 6 1826. Its apparent size is 11.9 by 0.7 arc minutes.NGC 2070
NGC 2070 is a large open cluster and candidate super star cluster located on the south-east corner of the Large Magellanic Cloud. It is located at the centre of the Tarantula Nebula and produces most of the energy that makes it visible. Its central condensation is the star cluster R136, one of the most energetic star clusters known. It holds a number of massive stars, including the most massive star known, R136a1, at 315 M☉ and 8.7 million L☉.NGC 2241
NGC 2241 is an open cluster in the constellation Dorado. Located in the Large Magellanic Cloud, it was discovered by John Herschel on January 31, 1835.