Large And Small Magellanic Clouds example essay topic

Clouds are usually the last things astronomers want to see in the sky, but for those who observe in the southern hemisphere there is a notable exception to that celestial rule. The Large and Small Magellanic Clouds are among the highlights of the southern night sky. Only within the last century were astronomers able to verify their true nature. Although they seem to be two foggy patches possibly torn from the Milky Way, astronomers believe these are actually small galaxies gravitationally bound to the Milky Way like moons around a giant planet. The two Clouds of Magellan are like binary stars that gravity draws together to form a satellite galaxy. Of all the galaxies in the entire Universe these are the closest to our galactic system.

About 170,000 light-years away from the Milky Way galaxy lie the Large Magellanic Cloud. With only 15 billion young bright stars, it is just one-quarter the size of our own galaxy. During the winter of 1987, a Canadian astronomer, Ian Shelton, spotted the first naked eye supernova since 1604, the result of a massive explosion. No more exciting and scientifically significant event has occurred over the last decade in science than Supernova 1987 A, as it is known. Photographs taken on the night of February 23, 1987, of the Large Magellanic Cloud, a companion galaxy to our own Galaxy, at Canada's southern hemisphere observatory at La Silla, Chile, and at the Siding Springs Observatory in Australia, revealed a 6th-magnitude object where only 12th-magnitude blue supergiant stars had been observed before.

Scientists believe that the progenitor of Supernova 1987 A is a typical blue supergiant of spectral type B 3. Spectra taken in 1977 do not suggest anything unusual happening in the outer layers of the star prior to undergoing the supernova outburst. This is not surprising since the real changes were occurring deep inside in a relatively tiny portion of the star's radius. The Large Cloud is quite important because it is the location of this Supernova 1987 A, the exploded star that for a time shone brightly but that is now dim and dead. Farther away than the Large Cloud, the Small Magellanic Cloud is approximately 200,000 light-years distant. It is roughly a third the size of the Large Cloud, consisting of only 5 billion older stars.

The nebula's were named after Portuguese explorer Ferdinand Magellan, the first person to sail around the world. Although the galaxies were visible long before Magellan's time and he was the first person to record studying them during his lengthy journey, the first detailed study of these galaxies were done by Sir John Herschel in the nineteenth century. While studying Cepheid variable stars in the Small Magellanic Clouds, Henrietta Leavitt discovered, in 1912, the period-luminosity relation. This relation offered a technique for measuring the distances of stars and galaxies.

These galaxies are classified as irregular because they show no definite symmetry or nucleus. With the technology we have available to us, there are other astronomers who believe that these clouds have somewhat of a spiral shape. We do know that the larger of the two, the Large Magellanic Cloud, is located mostly in the constellation Dorado and its angular diameter measures approximately 7^0. The Small Cloud is almost completely in the constellation Tucana and measures approximately 4^0 in diameter. The unique aspect of studying star formation in the Magellanic Clouds is that all the objects within a single galaxy lie at a common distance, so we can study the properties of star-forming cores, outflows, and photo dissociation regions from one cloud to another. In addition, the physical environment in the Magellanic Clouds (metalli city, radiation field, external pressure) is very different from that in the Milky Way.

The high sensitivity will be particularly important in studying outflow sources, which are identified by the presence of low-brightness high-velocity wings to the carbon lines in star-forming cores. The 30 Dora dus region of the Large Magellanic Clouds has recently formed a very dense star cluster similar to a young globular cluster. The diffuse nebulae in both the Large Magellanic Cloud and the Small Magellanic Cloud appear to have few elements heavier than helium. This deficiency is much more pronounced in the Small Magellanic Cloud. Supernova remnants are the primary source of energy within the interstellar medium. The million-degree gas in supernova remnant interiors is the main contributor to the 'hot phase' of the interstellar medium.

The details of supernova remnant expansion and evolution determine how this hot gas is distributed on large scales. The Large Magellanic Cloud provides a large sample (~ 40) of remnants from the supernova in various environments at a distance of 50 kp c. The Small Magellanic Cloud provides another such sample (~ 20), again at a known distance of 60 kp c. Supernova remnants in the Clouds of Magellan are observable with reasonable resolution and sensitivity, without Galactic uncertainties in distance and absorption. This makes these remnants ideal for population studies.

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Pictures web Oxygen Rich Supernova Remnant in the Large Magellanic Cloud. Supernova 1987 A Rings web.