Press Releases 2004

ESO Press Photos 34a-h/04

10 December 2004

For immediate release

Caught in the Cobweb

Turbulent and Colourful LMC Region Imaged from La Silla

ESO PR Photo 34a/04 Area around Ring-shaped Nebula DEM L 299 in the LMC (ESO/MPG 2.2-m + WFI) [Preview - JPEG: 400 x 466 pix - 240k] [Normal  - JPEG: 800 x 932 pix - 960k] [Large  - JPEG: 4000 x 4661 pix - 16.8M] [FullRes  - JPEG: 8394 x 9782 pix - 56.3M]

Caption: ESO PR Photo 34a/04 shows the turbulent region around the ring-shaped nebula DEM L 299 in the Large Magellanic Cloud, a satellite galaxy of the Milky Way system. It was produced by combining three monochromatic images obtained in December 2001 with the Wide-Field-Imager (WFI) at the ESO/MPG 2.2-m telescope at the La Silla Observatory. A description of various objects seen in this impressive sky field is available in the text; technical information will be found at the end of this Photo Release and some of the individual objects are shown in other photos below. The sky field measures 33.3 x 33.0 arcmin; the original pixel size (in the FullRes version) is 0.238 arcsec. North is up and East is left. The coloured rings seen near some of the brighter stars in the field result from light reflections in the telescope optics.

The Tarantula Nebula is one of the most impressive views in the Southern sky, cf. ESO Press Photos 14a-g/02. Visible to the unaided eye in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way that is located in the direction of the southern constellation Doradus at a distance of about 170,000 light-years, this huge nebula is the prototype of what astronomers refer to as a "Giant HII region". In this complex of glowing gas and very hot and luminous stars, the gas is mainly composed of protons and electrons, which are kept apart by energetic photons emitted by the stars in this area.

The Tarantula Nebula (also designated 30 Doradus) 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") resides that illuminate 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!

While the central regions of 30 Doradus may be compared to a tarantula, the entangled filaments in the outskirts of this nebula - some of which are seen in PR Photo 34a/04 - could well be likened with its cobweb. They testify to an ongoing history of very vigorous activity and make this spectacular sky region a showcase of dramatic effects caused by the tremendous output of energy from the most massive stars known.

Intricate colours

ESO PR Photo 34b/04 Filaments in the Tarantula Nebula in the LMC (ESO/MPG 2.2-m + WFI) [Preview - JPEG: 400 x 420 pix - 216k] [Normal  - JPEG: 800 x 839 pix - 656k] [FullRes  - JPEG: 1628 x 1708 pix - 2.7M]

Caption: ESO PR Photo 34b/04 shows filaments of ionized gas in the proximity of the R136 cluster, which lies beyond the lower left edge of the photo. The different hues are due to different physical conditions that manifest themselves in the spectrum of the light emitted by the gas. Note also the dark lanes running roughly from bottom left to upper right, which are due to filaments of obscuring dust seen in projection against the background of bright nebulosity. The sky field measures 6.5 x 5.7 arcmin. North is up and East is left.

The marvellous richness of the filament colours is due to the varying conditions in the interstellar gas in this region, cf. PR Photo 34b/04. The red in these images is caused by emission of excited hydrogen atoms, the green shades correspond to emission from oxygen atoms from which two electrons ("doubly-ionized oxygen") have been "knocked off" by the energetic radiation of hot stars in the R136 cluster, that is located beyond the lower right corner of this photo. The intensity of this emission increases towards R136, explaining the yellowish colour near the edge of the photo.

A blue colour is contributed by singly-ionized atoms of oxygen. Other atoms like nitrogen and sulfur at different levels of ionization also add to the emission of the nebula at specific wavelengths. The observed colours thus probe the physical condition of the emitting gas and the temperature of the star(s) that excite(s) it. The intricate appearance of the filaments is mostly a consequence of turbulence in the interstellar gas, of the magnetic fields, and of the energy input by the massive stars in the neighbourhood.

Supernovae blow interstellar "bubbles"

ESO PR Photo 34c/04 SNR 0543-689 in the LMC (ESO/MPG 2.2-m + WFI) [Preview - JPEG: 400 x 459 pix - 232k] [FullRes  - JPEG: 906 x 1039 pix - 1.1M]

ESO PR Photo 34d/04 SNR B0544-6910 in the LMC (ESO/MPG 2.2-m + WFI) [Preview - JPEG: 400 x 455 pix - 272k] [FullRes  - JPEG: 941 x 1071 pix - 1.3M]

Caption: ESO PR Photo 34c/04 shows a bright, compact nebula that is located on the North-Western rim of the ringshaped nebula DEM L 299. It is known as SNR 0543-689 and it is the remnant of a more recent supernova explosion. The sky field measures 3.6 x 3.5 arcmin. North is up and East is left. Another, even younger supernova remnant, B0544-6910 is shown in PR 34d/04. This sky field is located near the lower left corner of PR Photo 34a/04 and measures 3.7 x 3.6 arcmin; the orientation is the same.

The large ring-shaped nebula slightly to the lower-left (South-East) of the centre of PR 34a/04 is known as DEM L 299 [1]. Detailed investigations show that it represents an "interstellar bubble" which was "blown" by supernovae explosions, most probably happening millions of years ago, as massive stars near the centre of this structure ended their comparatively short lives in glorious flashes.

A closer inspection shows that another supernova exploded somewhat later near the rim, forming a bright and more compact nebula known as SNR 0543-689 (PR 34c/04). Other supernovae in this general field exploded even more recently, such as the one that created the remnant B0544-6910 (PR 34d/04) only a few tens of thousands of years ago, a blink of an eye by all astronomical standards.

Nebulae with built-in powerhouses

ESO PR Photo 34e/04 The N 164 Nebula in the LMC (ESO/MPG 2.2-m + WFI) [Preview - JPEG: 400 x 447 pix - 248k] [Normal  - JPEG: 800 x 894 pix - 736k] [FullRes  - JPEG: 1744 x 1949 pix - 3.3M]

ESO PR Photo 34f/04 The DEM L 297 Nebula in the LMC (ESO/MPG 2.2-m + WFI) [Preview - JPEG: 400 x 459 pix - 240k] [FullRes  - JPEG: 906 x 1039 pix - 1.2M]

Caption: ESO PR Photo 34e/04 shows N 164, a bright nebula, the glow of which is caused by hot stars inside it. The heating of the gas by these stars increases the pressure and causes such nebulae to expand, pushing outwards against their surroundings. A careful look at this nebula reveals locations where the expansion is encountering resistance by denser clouds of gas, producing bright, thin rims. The sky field measures 3.6 x 3.5 arcmin. North is up and East is left. PR Photo 34f/04 shows DEM L 297, another diffuse nebula that also glows due to stars embedded in it and whose "divided" appearance is due to the presence of obscuring dust lanes. The sky field measures 6.5 x 5.7 arcsec; the orientation is the same.

Not all the nebulae seen in this region are caused by supernovae, however. The glow of N 164 [1], a bright, extended red-yellow nebula just below DEM L 299, is mostly due to its own "private" powerhouse, that consists of several massive stars deeply embedded in its interior (PR Photo 34e/04).

The same holds for DEM L 297, the somewhat smaller and fainter nebula to the right of DEM L 299 (PR Photo 34f/04). It is divided into two half-circle formed segments by a dark lane of interstellar dust in front of it. Indeed, within the Tarantula complex many such dark and dusty clouds are seen in silhouette as they obscure bright nebulosity behind them.

Many stellar clusters

ESO PR Photo 34g/04 NGC 2093 Stellar Cluster in the LMC (ESO/MPG 2.2-m + WFI) [Preview - JPEG: 400 x 432 pix - 256k] [Normal  - JPEG: 800 x 864 pix - 760k] [FullRes  - JPEG: 1422 x 1535 pix - 2.2M]

ESO PR Photo 34h/04 NGC 2108 Stellar Cluster in the LMC (ESO/MPG 2.2-m + WFI) [Preview - JPEG: 400 x 450 pix - 248k] [FullRes  - JPEG: 702 x 789 pix - 680k]

Caption: ESO PR Photo 34g/04 shows the stellar cluster NGC 2093, a comparatively rich aggregate of young stars, a few tens of millions of years old. The hot temperature of the most massive of such young stars is responsible for its predominantly blue colour. The sky field measures 5.6 x 5.1 arcmin. North is up and East is left. ESO PR Photo 34h/04 shows the stellar cluster NGC 2108, a rich "mid-aged" cluster, about 600 million years old. A careful comparison with its neighbour NGC 2093 (PR Photo 34g/04) shows that the brightest stars of NGC 2108 are fainter and whiter than the brightest members of NGC 2093; this indicates that NGC 2108 is older. Note also the distinctly red star to the East (left) of the center of this cluster. This is a member of a stellar class referred to as "Carbon stars", cool giant stars that are characterized by the presence of carbon molecules (C2) in their atmospheres and having extremely red colours. This sky field measures 2.8 x 2.6 arcsec; the orientation is the same.

The outskirts of the Tarantula Nebula are also rich in stellar clusters. One of them, NGC 2093 [1], cf. PR Photo 34g/04, has relatively few stars and is relatively young, just a few tens of millions of years. It appears that its stars have already excavated a sizeable cavity around them that is now relatively void of gas.

An older and much more compact cluster, NGC 2108, is seen near the bottom of PR Photo 34a/04 and reproduced in full in PR Photo 34a/04. It resembles the globular clusters in our own Galaxy, but it formed much more recently, about 600 million years ago. Still, NGC 2108 is much older than the Tarantula complex and it is quite possible that in its "youth" it was the core of another giant HII region that has since dissolved into interstellar space.

The images for this release were produced by two ESO astronomers who are impressed by this sky region. Nausicaa Delmotte did the observations for her thesis and notes that: "many of the nebulae and clusters seen in these photos would stand out prominently if they were located elsewhere in the sky and not this close to the core of the spectacular Tarantula complex.". She is echoed by her colleague, Fernando Comeron: "This amazing concentration of clusters, HII regions, supernova remnants, and extremely hot and luminous stars in a single region makes the Tarantula in the LMC a unique celestial object, unrivalled in our own Galaxy and other nearby galaxies!".

Note

[1]: The designation "DEM L 299" indicates that this object is no. 299 in the list of nebulae in the Large and Small Magellanic Clouds published in 1976 by astronomers R.D.Davies, K.H.Elliott and J.Meaburn. "N" refers to a list of bright nebulae in these galaxies that was compiled in 1956 by K.G.Henize. "NGC" stands for the "New General Catalogue" published in 1888 by J.L.E. Dreyer.

Technical information

The present colour photo of the Northeastern outskirts of the Tarantula nebula in the Large Magellanic Cloud is based on three monochromatic images taken on 6 and 7 December 2001 with the Wide-Field-Imager (WFI) at the ESO/MPG 2.2-m telescope, through an U-band filter (with the forbidden emission line of singly-ionised oxygen, [OII], at wavelength 372.7 nm) and two narrow-band filters centred on the wavelengths of the forbidden line of doubly-ionised oxygen ([OIII], at 500.7 nm) and hydrogen (H-alpha line, at 656.2 nm), respectively. Each single-colour image is in turn composed of four individual frames of 20 minutes of exposure time each. The WFI detector system is composed of eight individual 2k x 4k CCDs with small gaps between them; for this reason, the individual frames in each filter were obtained with the telescope pointing at slightly different positions in the sky, so that the parts of the sky falling in the detector gaps in any given frame are recorded on the others. A problem with one of the detector chips causes double stellar images to appear over a small, narrow strip near the upper left edge of the full field image. The monochromatic images were produced by superimposing the individual frames, correcting for the telescope offsets. Finally, the combined images in each filter were aligned and colour-coded to produce the resulting colour picture. North is up and East is left. The extensive image processing was performed by ESO-astronomers Fernando Comeron and Nausicaa Delmotte.