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Post Info TOPIC: Tarantula nebula


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30 Doradus Nebula
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hs-2009-32-a-web.jpg
Credit NASA

Just in time for the holidays: a Hubble Space Telescope picture postcard of hundreds of brilliant blue stars wreathed by warm, glowing clouds. The festive portrait is the most detailed view of the largest stellar nursery in our local galactic neighbourhood. The massive, young stellar grouping, called R136, is only a few million years old and resides in the 30 Doradus Nebula, a turbulent star-birth region in the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way. There is no known star-forming region in our galaxy as large or as prolific as 30 Doradus. Many of the diamond-like icy blue stars are among the most massive stars known. Several of them are over 100 times more massive than our Sun. These hefty stars are destined to pop off, like a string of firecrackers, as supernovas in a few million years.
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Posts: 131433
Date:
30 Doradus
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Title: Physical Conditions in the Ionized Gas of 30 Doradus
Authors: R. Indebetouw, G. E. de Messières, S. Madden, C. Engelbracht, J. D. Smith, M. Meixner, B. Brandl, L. J. Smith, F. Boulanger, F. Galliano, K. Gordon, J. L. Hora, M. Sewilo, A. G. G. M. Tielens, M. Werner, M. G. Wolfire

We present a mid-infrared spectroscopic data cube of the central part of 30 Doradus, observed with Spitzer's IRS and MIPS/SED mode. Aromatic dust emission features and emission lines from molecular and atomic hydrogen are detected but not particularly strong. The dominant spectral features are emission lines from moderately ionised species of argon, neon, and sulphur, which are used to determine the physical conditions in the ionised gas. The ionised gas excitation shows strong variations on parsec scales, some of which can plausibly be associated with individual hot stars. We fit the ionic line strengths with photoionisation and shock models, and find that photoionisation dominates in the region. The ionisation parameter U traces the rim of the central bubble, as well as highlighting isolated sources of ionisation, and at least one quiescent clump. The hardness of the ionising radiation field T_rad reveals several "hot spots" that are either the result of individual very hot stars or trace the propagation of the diffuse ionising field through the surrounding neutral cloud. Consistent with other measurements of giant molecular hydrogen regions, log(U) ranges between -3 and -0.75, and T_rad between 30000 and 85000K.

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Title: The chemical composition of NGC 3603, 30 Doradus and N 66 from Spitzer/IRS observations
Authors: V. Lebouteiller, J. Bernard-Salas, B. Brandl, D. Whelan, Y. Wu, V. Charmandaris, D. Devost

We investigate the chemical abundances of NGC 3603 in the Milky Way, of 30 Doradus in the Large Magellanic Cloud, and of N 66 in the Small Magellanic Cloud. The mid-infrared observations with the Infrared Spectrograph onboard the Spitzer Space Telescope allow us to probe spectra toward distinct physical regions within each object, the central ionising cluster, the surrounding ionised gas, photodissociation-regions, and buried stellar clusters. We detect [SIII], [SIV], [ArIII], [NeII], [NeIII], [FeII], and [FeIII] lines and derive the ionic abundances. Based on the ionic abundance ratio (NeIII/H)/(SIII/H), we find that the gas probed in the MIR is characterized by a higher degree of ionization than the gas probed with optical spectra. We compute the elemental abundances of Ne, S, Ar, and Fe. We find that the alpha-elements Ne, S, and Ar scale with each other. Our determinations agree well with the abundances derived from the optical. The Ne/S ratio is higher than the solar proportion between Ne and S and points toward a moderate depletion of sulphur on dust grains. We find remarkably homogeneous neon and sulphur abundances (0.11 dex in 15 positions in 30 Doradus), suggesting a relatively homogenous ISM. Small-scale mixing cannot be ruled out.

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256 Million Pixel Image of Immense Stellar Factory
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A new, stunning image of the cosmic spider, the Tarantula Nebula and its surroundings, finally pays tribute to this amazing, vast and intricately sculpted web of stars and gas. The newly released image, made with ESO's Wide Field Imager on the 2.2-m ESO/MPG Telescope at La Silla, covers 1 square degree on the sky and could therefore contain four times the full Moon.
Known as the Tarantula Nebula for its spidery appearance, the 30 Doradus complex is a monstrous stellar factory. It is the largest emission nebula in the sky, and can be seen far down in the southern sky at a distance of about 170,000 light-years, in the southern constellation Dorado (The Swordfish or the Goldfish). It is part of one of the Milky Way's neighbouring galaxies, the Large Magellanic Cloud.
The Tarantula Nebula is thought to contain more than half a million times the mass of the Sun in gas and this vast, blazing labyrinth hosts some of the most massive stars known. The nebula owes its name to the arrangement of its brightest patches of nebulosity, that somewhat resemble the legs of a spider. They extend from a central 'body' where a cluster of hot stars (designated 'R136') illuminates and shapes the nebula. This name, of the biggest spiders on the Earth, is also very fitting in view of the gigantic proportions of the celestial nebula - it measures nearly 1,000 light-years across and extends over more than one third of a degree: almost, but not quite, the size of the full Moon. If it were in our own Galaxy, at the distance of another stellar nursery, the Orion Nebula (1,500 light-years away), it would cover one quarter of the sky and even be visible in daylight.
Because astronomers believe that most of the stars in the Universe were formed in large and hectic nurseries such as the 30 Doradus region, its study is fundamental. Early this year, astronomers took a new, wide look at the spider and its web of filaments, using the Wide Field Imager on the 2.2-m MPG/ESO telescope located at La Silla, Chile, while studying the dark clouds in the region. Dark clouds are enormous clouds of gas and dust, with a mass surpassing a million times that of the Sun. They are very cold, with temperatures about -260 degrees Celsius, and are difficult to study because of the heavy walls of dust behind which they hide. Their study is however essential, as it is in their freezing wombs that stars are born.

Observing in four different bands, the astronomers made a mosaic of the half-degree field of view of the instrument to obtain an image covering one square degree. With each individual image containing 64 million pixels, the resultant mosaic thus contained 4 times as many, or 256 million pixels! The observations were made in very good image quality, the 'seeing' being typically below 1 arcsecond.

The image is based on data collected through four filters, including two narrow-band filters that trace hydrogen (red) and oxygen (green). The predominance of green in the Tarantula is a result of the younger, hotter stars in this region of the complex.
It would be easy to get lost in the meanderings of the filamentary structures or get stuck in the web of the giant arachnid, as is easily experienced with the zoom-in feature provided on the associated photo page, and it is therefore difficult to mention all the unique objects to be discovered. Deserving closer attention perhaps is the area at the right-hand border of the Tarantula. It contains the remains of a star that exploded and was seen with the unaided eye in February 1987, i.e. almost 20 years ago. Supernova SN 1987A, as it is known, is the brightest supernova since the one observed by the German astronomer Kepler in 1604. The supernova is known to be surrounded by a ring, which can be distinguished in the image.
A little to the left of SN 1987A, another distinctive feature is apparent: the Honeycomb Nebula. This characteristic bubble-like structure results apparently from the interaction of a supernova explosion with an existing giant shell, which was itself generated by the combined action of strong winds from young, massive stars and supernova explosions.

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Posts: 131433
Date:
Tarantula nebula
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Hanging above the Large Magellanic Cloud (LMC) - one of our closest galaxies - in what some describe as a frightening sight, the Tarantula nebula is worth looking at in detail. Also designated 30 Doradus or NGC 2070, the nebula owes its name to the arrangement of its brightest patches of nebulosity that somewhat resemble the legs of a spider. This name, of the biggest spiders on Earth, is also very fitting in view of the gigantic proportions of the celestial nebula - it measures nearly 1,000 light years across!


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Position(2000): RA = 05 : 38.7 Dec = -69 : 06

The Tarantula nebula (NGC 2070) is the largest emission nebula in the sky and also one of the largest known star-forming regions in all the Milky Way's neighbouring galaxies. Located about 168,000 light years away, in the southern constellation Dorado (The Swordfish), it can be seen with the unaided eye.


Tarantula's Central Cluster, R136

This image was obtained with the FORS1 multi-mode instrument on Eso's Very Large Telescope, its structure is fascinatingly complex, with a large number of bright arcs and apparently dark areas in between. Inside the giant emission nebula lies a cluster of young, massive and hot stars, denoted R 136, whose intense radiation and strong winds make the nebula glow, shaping it into the form of a giant arachnid. The cluster is about 2 to 3 million years old, that is, almost from 'yesterday' in the 13.7 billion year history of the Universe.

Several of the brighter members in the immediate surroundings of the dense cluster are among the most massive stars known, with masses well above 50 times the mass of our Sun. The cluster itself contains more than 200 massive stars.


Position (2000): R.A. 5h 38m 27s Dec. -69° 04' 26"

In the upper right of the image, another cluster of bright, massive stars is seen. Known to astronomers as Hodge 301, it is about 20 million years old, or about 10 times older than R136. The more massive stars of Hodge 301 have therefore already exploded as supernovae, blasting material away at tremendous speed and creating a web of entangled filaments. More explosions will come soon - in astronomical terms - as three red supergiants are indeed present in Hodge 301 that will end their life in the gigantic firework of a supernova within the next million years.

While some stars are dying in this spidery cosmic inferno, others are yet to be born. Some structures, seen in the lower part of the image, have the appearance of elephant trunks, not unlike the famous and fertile "Pillars of Creation" at the top of which stars are forming. In fact, it seems that stars form all over the place in this gigantic stellar nursery and in all possible masses, at least down to the mass of our Sun. In some places, in a marvellous recycling process, it is the extreme radiation from the hot and massive stars and the shocks created by the supernova explosions that has compressed the gas to such extent to allow stars to form.

To the right and slightly below the central cluster, a red bubble is visible. The star that blows the material making this bubble is thought to be 20 times more massive, 130 000 times more luminous, 10 times larger and 6 times hotter than our Sun. A possible fainter example of such a bubble is also visible just above the large red bubble in the image.

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