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
constellationsDorado 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.[14]
The LMC is predicted to merge with the Milky Way in approximately 2.4 billion years.[15]
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.[17][18] However, this seems to be a misunderstanding of a reference to some stars south of
Canopus which he admits he has not seen.[19][20]
The first confirmed recorded observation was in 1503–1504 by
Amerigo Vespucci in a letter about his third voyage. He mentioned "three Canopes [sic], two bright and one obscure"; "bright" refers to the two
Magellanic Clouds, and "obscure" refers to the
Coalsack.[21]
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.[18]
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.[22]
The Large Magellanic Cloud has a prominent central bar and
spiral arm.[24] The central bar seems to be warped so that the east and west ends are nearer the Milky Way than the middle.[25] In 2014, measurements from the Hubble Space Telescope made it possible to determine a rotation period of 250 million years.[26]
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[27] 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,[28] by core helium-burning red clump stars,[29] and by the tip of the red giant branch.[30] 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[30] and flared,[31][32] likely due to interactions with the SMC.[32] Regarding the distribution of
star clusters in the LMC,
Schommer et al.[33] 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.,[34] 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
Distance to the LMC has been calculated using
standard candles;
Cepheid variables are one of the most popular. These have been shown to have a relationship between their absolute luminosity and the period over which their brightness varies. However the variable of metallicity may also need to be taken as a component of this as consensus is this likely affects their
period-luminosity relations. Unfortunately, those in the Milky Way typically used to calibrate the relation are more metal-rich than those found in the LMC.[35]
In 2006, the Cepheid absolute luminosity was re-calibrated using Cepheid variables in the galaxy
Messier 106 that cover a range of metallicities.[8] Using this improved calibration, they find an absolute
distance modulus of , or 48 kpc (160,000 light-years). This distance has been confirmed by other authors.[9][10]
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.[2]
Features
Like many
irregular galaxies, the LMC is rich in gas and dust, and is currently undergoing vigorous
star formation activity.[37] It holds the
Tarantula Nebula, the most active star-forming region in the Local Group.
A
bridge of gas connects the Small Magellanic Cloud (SMC) with the LMC, which evinces tidal interaction between the galaxies.[42] The Magellanic Clouds have a common envelope of neutral hydrogen, indicating that they have been gravitationally bound for a long time. This bridge of gas is a star-forming site.[43]
X-ray sources
No X-rays above background were detected from either cloud during the September 20, 1966,
Nike-Tomahawk rocket flight nor that of two days later.[44] The second took off from
Johnston Atoll at 17:13 UTC and reached an apogee of 160 km (99 mi), with spin-stabilization at 5.6 rps.[45] The LMC was not detected in the X-ray range 8–80 keV.[45]
Another was launched from same atoll at 11:32 UTC on October 29, 1968, to scan the LMC for X-rays.[46] The first discrete X-ray source in
Dorado was at
RA05h 20mDec −69°,[46][47] and it was the Large Magellanic Cloud.[48] 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 4×1038ergs/s.[46] An
X-ray astronomy instrument was carried aboard a
Thor missile launched from the same atoll on September 24, 1970, at 12:54 UTC and altitudes above 300 km (190 mi), to search for the
Small Magellanic Cloud and to extend observation of the LMC.[49] The source in the LMC appeared extended and contained star
ε Dor. The X-ray luminosity (Lx) over the range 1.5–12 keV was 6×1031W (6×1038 erg/s).[49]
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
RA05h 40m 05sDec −69° 45′ 51″, and is a high-mass X-ray binary (star system) source (
HMXB).[50] 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 one that is a bright low-mass X-ray binary system (
LMXB) in the LMC.[51]
DEM L316 in the Cloud consists of two supernova remnants.[52]Chandra X-ray spectra show that the hot gas shell on the upper left has an abundance of iron. This implies that the upper-left
SNR is the product of a
Type Ia supernova; much lower such abundance in the lower remnant belies a
Type II supernova.[52]
A 16 ms X-ray pulsar is associated with SNR 0538-69.1.[53] SNR 0540-697 was resolved using
ROSAT.[54]
Gallery
Part of the SMASH dataset showing a wide-angle view of the Large Magellanic Cloud[55]
Large Magellanic Cloud as photographed by an amateur astronomer. Unrelated stars have been edited out.
Large Magellanic Cloud rendered from Gaia EDR3
Large Magellanic Cloud rendered from Gaia EDR3 without foreground stars
Revisiting a Celestial Fireworks Display Shreds, from the
Wide Field Planetary Camera 2. The delicate sheets and intricate filaments are debris from the cataclysmic death of a massive star that once lived in the LMC.[56]
DEM L316A is located some 160,000 light-years away in the Large Magellanic Cloud[57]
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