خانه / Science / Astronomy / Large Magellanic Clouds

Large Magellanic Clouds

Large Magellanic Cloud-8sec

Large Magellanic Clouds

The Large Magellanic Cloud (LMC) is a satellite dwarf galaxy of the Milky Way that is among the closest galaxies to Earth. At about 163,000 light-years from Earth, the dwarf galaxy looks like a faint cloud in Southern Hemisphere skies. It lies on the border of the constellations Dorado and Mensa.

Both the LMC and its companion, the Small Magellanic Cloud, are named after Ferdinand Magellan . While astronomers in the Southern Hemisphere saw them before Magellan’s round-the-world voyage in 1519, NASA said, the explorer and his crew were the first to bring that knowledge to the Western world.

Magellan died during that voyage in the Philippines, but his crew provided documentation of the discovery upon their return to Europe.

Its shape suggests a transitional form between a small spiral galaxy and an irregular galaxy. About 30,000 light years across in the longest dimension, it appears from Earth more than 20 times the width of a full moon.

Estimates vary from a few billion to perhaps 10 billion stars in this galaxy, at best no more than about one-tenth the mass of the Milky Way.

The center of the LMC is approximately RA: 5h 23m 35s, dec: -69°45’22”

Once cosmic distances were better understood through tools such as using “standard candles” (objects with known luminosities, such as certain types of variable stars), the LMC was considered the closest galactic object to Earth until 1994, when astronomers found the Sagittarius Dwarf Elliptical Galaxy, NASA said. Another discovery in 2003 — the Canis Major Dwarf Galaxy — turned out to be even closer.

From tropical latitudes in the Northern Hemisphere, where it still can be observed, the LMC is best seen in the evening from December to April. When the constellation Orion reaches its highest point in the sky, so does the Large Magellanic Cloud. But even at 15 degrees north latitude (the latitude of Central America), the LMC never gets far above the southern horizon.

Besides its proximity to Earth, the LMC is a location for starbirth. Within its borders, several observatories from NASA and others have captured vast amounts of gas coming together to create young stars.

A 2012 composite image of the Tarantula Nebula – more properly known as 30 Doradus – revealed violence and radiation through the eyes of the Hubble, Chandra and Spitzer space telescopes. “At the center of 30 Doradus, thousands of massive stars are blowing off material and producing intense radiation along with powerful winds,” NASA wrote at the time.

“The Chandra X-ray Observatory detects gas that has been heated to millions of degrees by these stellar winds and also by supernova explosions. These X-rays … come from shock fronts-similar to sonic booms-formed by this high-energy stellar activity.”

A smaller star-forming region within the LMC is in a spot known as LHA 120-N 11 . The LMC in general is an excellent spot to look for stars being born, NASA said in a statement accompanying an image of that region.

“It lies in a fortuitous location in the sky, far enough from the plane of the Milky Way that it is neither outshone by too many nearby stars, nor obscured by the dust in the Milky Way’s center,” NASA stated. It is also close enough to study in detail (less than a 10th of the distance to the Andromeda Galaxy, the closest spiral galaxy), and lies almost face-on to us, giving us a bird’s eye view.”

The LMC’s relatively close location to Earth also affords astronomers the chance to study it in more detail, with the aim of using that understanding to extrapolate to how other galaxies behave. One example is through its rotation , which was picked up by the Hubble Space Telescope in results released in February 2014.

“Studying this nearby galaxy by tracking the stars’ movements gives us a better understanding of the internal structure of disk galaxies,” said Nitya Kallivayalil, a researcher at the University of Virginia who participated in the research, in a statement. “Knowing a galaxy’s rotation rate offers insight into how a galaxy formed, and it can be used to calculate its mass.”

The researchers discovered that the LMC makes a rotation every 250 million years. They found this by using Hubble to track the motion of stars in the galaxies sideways with respect to the plane of the sky. While this technique has been used for more nearby objects before, this effort represented the first time it was used for a galaxy.

History and myth of the Large Magellanic Cloud. Being so far south on the sky’s dome, the Large Magellanic Cloud was not known in classical northern mythology at all. Understandably, it factors better for observers in the Southern Hemisphere. The nearby constellation, Mensa (“Table”), originally was named after South Africa’s Table Mountain, and a story from that country equates the Large Magellanic Cloud with a puff of smoke from a pipe-smoking contest held on the mountain. Australian Aboriginal storytellers relate that the LMC is the campsite of an old man, whereas the Small Magellanic Cloud (SMC) is the campsite of his wife. The couple, known jointly as Jukara, had grown too old to feed themselves, so other star beings bring them fish from the sky river we know as the Milky Way.



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