30 October 2016 | Stars and Gas in the LMC

 

A familiar sight to amateur astronomers in the southern hemisphere, the Large Magellanic Cloud (LMC) along with the Small Magellanic Cloud (SMC) are satellite galaxies of the Milky Way that are easily visible in the night sky.

This deep telescopic 3 frame mosaic spanning 6×2 degrees focuses on the central part of the LMC and shows its stellar disk in immaculate clarity as it was taken from a remote observatory located under extremely dark skies in the Atacama Desert in Chile.

Named after the explorer Ferdinand Magellan who made their presence in the sky first known to Europe and the northern hemisphere in general, the Magellanic Clouds were already known to people living in the southern hemisphere and factor into the myths and legends of various civilizations including the Australian Aborigines. The esteemed Persian astronomer al-Sufi made the first recorded mention of the LMC in the Book of Fixed Stars, which was published in 964 AD.

The LMC was originally believed to be an irregular galaxy but deep observations have established it as the prototype of a class of galaxy known as Magellanic barred spirals. The LMC is estimated to be between 160,000 and 180,000 light years away making it one of the nearest galaxies to us. Its relative proximity allows the full splendour of its cosmic treasures to be observed and studied in clear detail by both amateur and professional astronomers! It is a treasure trove of hundreds of clusters and nebulae with many targets that can be observed by visual observers and concurrently provides a huge wealth of imaging targets for amateur astrophotographers.

Whilst the majority of the LMC is located within the confines of the constellation of Dorado, the southern part of it occupies the constellation Mensa. In addition to this, some of the outlying clusters belonging to it can be found in the neighboring constellations of Hydrus, Reticulum and Pictor.

The rich dense starfields of the LMC are studded with multiple ruby red emission nebulae and HII regions. The largest and most prominent of these is known as the Tarantula Nebula and officially catalogued as NGC 2070. With a gargantuan size of more than 1000 light years, this iconic nebula is bright enough to be glimpsed with the eye under dark skies despite being located in another galaxy! It is of such enormity that if it were located at the distance of the nearby Orion Nebula, it would occupy an area equivalent to half the sky! Other notable nebulae include the round bubble NGC 1966 at top centre and the superbubble N186 near the bottom right corner.

Many gemstones of sparkling clusters and starclouds coruscate along the glittery silvery fabric of the starfields in the LMC with their blue colour an indicator of their youth. The cluster system of the LMC is of great interest to professional astronomers as they are representative of all stages of evolution. In fact, the LMC contains different types of objects that have no counterpart in the Milky Way! Some of these are a class of young blue clusters known as “blue globular clusters” as the globular cluster population of the Milky Way is of an old age of billions of years. Examples of this type of cluster have been observed in other galaxies.

The LMC is home to thousands of clusters and OB associations with more being discovered all the time. Prominent clusters visible in this image include the young 15 million year old open cluster NGC 2100 to the left of the Tarantula Nebula and visible near the top right corner is the globular cluster NGC 1850, which is surrounded by a red filamentary HII region. Other iridescent examples include a pair towards the bottom of the image south of the Tarantula Nebula, these are NGC 2058 (the upper one) and NGC 2065 (the lower of the two).

Mouseover the image for a spectacular view of the ionized hydrogen gas with an exposure time of almost 20 hours! Taken with a Ha filter, it reveals a great deal of filamentary structures and superbubbles and generally much more fainter nebulosity is revealed in abundance in comparison with the RGB image. In addition to Ha, the vast collection of nebulae in the LMC also exhibit significant OIII emission. The ionized gas visible hints at a substantial amount of star formation taking place in this galaxy presumably triggered by interactions with its neighbour, the Small Magellanic Cloud. Conversely, the LMC is a hive of stardeath with a colourful collection of supernova remnants as well as a large population of Wolf Rayet stars and a number of associated Wolf Rayet nebulae discovered in the past few decades.

Many of the nebulae in the LMC are included in the Henize nebula catalogue published by the astronomer Karl Henize in 1956. Subsequent mapping of the nebular medium of the LMC resulted in the publication of the DEM nebula catalogue by the astronomers R. Davies, K. Elliott and J. Meaburn in 1976. More recently in the 21st century, the Magellanic Cloud Emission Line Survey (MCELS) has uncovered even fainter nebulae. Adding to the confusion of cataloguing and identifying the splendiferous treasure trove of cosmic jewels in the LMC, all three catalogues have equivalent listings of nebulae in the SMC! A Ha mosaic by John Gleason that shows a larger area of the LMC can be viewed here.

Following the first detailed mapping of the ionized ISM of the LMC in the 1970’s, many revelations regarding the large scale structure of the gas had arisen. The most major of these were the discovery of the majority of the star formation and gas being organized in huge large scale structures, which were later dubbed supergiant shells with sizes of thousands of light years! Their formation is believed to be linked to the activity of fast stellar winds and multiple supernova explosions of massive stars located in clusters and OB associations. The Tarantula Nebula is situated within ribbons of gas that comprises a supergiant shell known as LMC 2, which exhibits the brightest and most coherent filamentary structure of the nine known supergiant shells in the LMC and also has a huge size of approximately 3000 light years.

Besides the well known Tarantula Nebula, the LMC contains hundreds of other interesting targets that are worthy of imaging by both amateur astrophotographers and professional observatories. As well as being explored photographically, the beauty of the LMC can be appreciated by visual observers with a delectable assortment of sparkly clusters and starclouds and observing the various Magellanic jewels is likely to result in the release of serotonin and endorphins being triggered in the brain! For people in the southern hemisphere who don’t own or have access to a telescope, the LMC can be seen with the unaided eye as a misty cloudy patch in the night sky. Looking up at the night sky is greatly encouraged and a sense of wonder and magic of the universe should be kept alive in the heart!

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