Large Magellanic Galaxy

The largest satellite galaxy in the Milky Way

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synonym Large Magellanic Cloud (Galaxy) generally refers to the Large Magellanic Galaxy

Large Magellanic Galaxy（ Large Magellanic Cloud， Abbreviation LMC ； Also known as Big Magellanic Cloud Barley cloud^[1] ）, Yes Local galaxy group Medium famous Extragalactic galaxy One of Dwarf galaxy 。 It is Galaxy numerous Satellite galaxy The one with the largest mass in the Swordfish and Mountain bench Junction, about 160000 Light year^[3] , about 1/20 of the diameter of the Milky Way, fixed star The number is about 1/10 of the Milky Way (about 10 billion).

Large Magellan Galaxy yes Local galaxy group The fourth largest galaxy in the Triangle galaxy （M33）、 Galaxy And Andromeda galaxy （ M31 ）。

Chinese name: Large Magellanic Galaxy
Foreign name: Large Magellanic Cloud
Alias: Large Magellanic Cloud
Classification: SB(s)m
Quality: About 1 ✕ 10 ten M⊙^[3]
Apparent magnitude: 0.9 etc

Rotation period: About 250 M yr
Right ascension: 05:23:34.5s
Declination: -69°45′22″^[2]
Distance from ground: About 163000 light years
Apparent diameter: 10.75°×9.17°
Redshift: 278±3 km/s^[2]

catalog

four shape
five distance
six observation

seven Record

Morphology and observation history

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The shape of the Large Magellanic Galaxy is similar Irregular galaxy , but it seems that there are some Helical structure Marks. Some speculate that the Large Magellanic Galaxy was Barred spiral galaxy , influenced by the galactic Gravitational disturbance It becomes an irregular galaxy, so it still remains in the center Stub Structure of. stay NASA Of Extragalactic galaxy In the database according to Hubble sequence It is classified as "Irr/SB (s) m".

stay southern hemisphere The Large Magellanic Galaxy is a dark celestial bodies , on Mountain bench and Swordfish Between the boundaries of two constellations. Its name comes from the navigator Ferdinand Magellan , observed its relationship with Magellanic galaxy （SMC）。 In fact, as early as about 964 AD, Persia astronomer Abdul Rahman Sufi Already in his book《 Book of Stars 》(Book of Fixed Stars).

position

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Magellanic cloud position relative to the Milky Way

GMW ——Large Magellanic Galaxy（ LMC ）
KMW —— Magellanic galaxy （SMC）
GSP —— Galactic coordinate system
MSI —— Magellanic Stream
three —— tarantula nebula （NGC 2070）
W ——SMC wing^[15]

Note: The green arrow at the bottom left of the figure indicates Magellan Cloud be relative to Galactic center Of Direction of movement 。

features

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The Milky Way, the Large Magellanic Galaxy and the Small Magellanic Galaxy seen in the southern hemisphere are on the right

Like many irregular galaxies, the Large Magellanic Galaxy is rich in gas and Interstellar matter , and is experiencing obvious Star formation activity^[4] 。 This massive star formation phenomenon may be due to the fact that the Large Magellanic Galaxy is affected by the Milky Way Tidal force Impact. In addition, the tidal force of the Milky Way also stripped some stars and interstellar matter from the Large Magellanic Galaxy, forming a long Magellanic Stream 。

60 have been found in the Large Magellanic Galaxy Globular cluster , 400 Planetary nebula And 700 Open cluster And hundreds of thousands of superstars and Supergiant 。 It has a stick shaped core composed of old red stars, surrounded by younger blue stars.

shape

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The Large Magellanic Galaxy is usually regarded as an irregular galaxy, but it shows signs of rod structure, so it was once reclassified as a Magellanic dwarf spiral galaxy 。

There is a remarkable Central rod and Spiral arm^[5] 。 The central bar seems to be slightly twisted, and the east and west ends are closer to the Milky Way than the center^[6] 。 utilize Hubble Space Telescope And measured its Rotation period About 250 million years.

For a long time, the Large Magellanic Galaxy has been considered as a "two-dimensional plane" galaxy with a single distance from the Milky Way. But, Cordway and Cowson discovered the Cepheid variable Closer to the Milky Way than Cepheid variables in the southwest^[7] 。 Through observation Other Cepheid variables in the field, red clusters of core burning helium and Red Giant The observation of branches and others confirmed this geometric tilt.^[8-10] The tilt obtained from these papers is about 35 °, and the tilt of the galaxy facing the Milky Way is set as 0 °. utilize Carbon star kinematics Further research shows that the disk structure of the Large Magellanic Galaxy is composed of two thick slices and outward tilt^[10-11] 。 About the Large Magellanic Galaxy cluster Shoemaker et al. measured the velocities of about 80 star clusters, and found that the group kinematics in the Large Magellanic Galaxy is consistent with the cluster motion of disk like distribution^[12] 。 These results have also been confirmed by Cordway et al., who calculated the distance of some star clusters in the Large Magellanic Galaxy, showing that their distribution is the same as the plane of the star field.^[13]

distance

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The distance of the Large Magellanic Galaxy has been measured for many years, and the values have changed greatly. The main difficulty is that as an extragalactic Measuring distance Standard candle Of Cepheid variable and RR Lyrae variable , Intragalactic parallax It has not been calibrated accurately; Another reason is that the Amount of metal Low right luminous efficiency The impact of is not yet known.

In the past few years, the distance has been confirmed within the range of 155000~165000 light years Distance modulus Of Estimated value It's 18.56, about 51.5 kiloseconds 。^[14]

observation

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In August 2022, researchers from the National Astronomical Observatory of the Chinese Academy of Sciences released the first batch of celestial body widths observed by EP-WXT pathfinder field X-ray Images and Energy spectrum 。 The instrument also observed the Adjacent galaxy ——Large Magellanic Cloud, one observation can cover the entire Large Magellanic Cloud galaxy.^[16]

Record

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Large Magellanic Cloud Distance Galactic center 160000 light years, with a diameter of about 20000 light years, and a mass equivalent to 10 billion sunlight , (Guinness World Records for the Largest Satellite Galaxy ）。^[17]

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