Picture of the Week

9 March 2009

First Light for the Active Phasing Experiment — a step towards the E-ELT

The 40-metre-class primary mirror of the European Extremely Large Telescope (E-ELT) will be composed of 984 individual segments, which must be aligned with incredible precision.

The position of the individual hexagonal mirrors needs to be controlled with nanometre precision (1 nanometre is 1 millionth of a mm). This can only be achieved with the help of new technologies and a prototype component for this high-tech alignment of segmented mirrors is seen in this image.

The so-called Active Phasing Experiment achieved its First Light during the night of 6 December 2008 on the visitor focus of Melipal, one of the 8.2 m Unit Telescopes of ESO’s Very Large Telescope at Paranal. Made in collaboration with several European partners, the current active segmented mirror is composed of 61 hexagonal segments.

You can move around the experiment in this Quicktime VTR animation.

2 March 2009

The Sombrero Galaxy

One of most famous spiral galaxies is Messier 104, widely known as the "Sombrero" (the Mexican hat) because of its particular shape. It is located towards the constellation Virgo (the ‘virgin’), at a distance of about 30 million light-years and is the 104th object in the famous catalogue of deep-sky objects by French astronomer Charles Messier (1730 - 1817).

This luminous and massive galaxy has a total mass of about 800 billion suns, and is notable for its dominant nuclear bulge, composed mainly of mature stars, and its nearly edge-on disc composed of stars, gas, and dust. The complexity of this dust is apparent directly in front of the bright nucleus, but is also evident in the dark absorbing lanes throughout the disc. A large number of small, diffuse objects can be seen as a swarm in the halo of Messier 104. Most of these are globular clusters, similar to those found in our own Milky Way, but Messier 104 has a much larger number of them. This galaxy also appears to host a supermassive black hole of about 1 billion solar masses, one of the most massive black holes measured in any nearby galaxy, and 250 times larger than the black hole in the Milky Way. Despite having such a massive black hole at its centre, the galaxy is rather quiet, implying that the black hole is on a very stringent diet.

This image is based on data acquired with the 1.5 m Danish telescope at the ESO La Silla Observatory in Chile, through three filters (B: 120 s, V: 100 s, R: 100 s).

23 February 2009

Startrails over Cerro Paranal in 1987

A view of Paranal from May 1987.

16 February 2009

Cosmic Butterfly

The Bug Nebula, NGC 6302, is one of the brightest and most extreme planetary nebulae known. It is located about 4,000 light-years away, towards the Scorpius constellation (the Scorpion). The nebula is the swansong of a dying solar-like star lying at its centre. At about 250,000 degrees Celsius and smothered in a blanket of hailstones, the star itself has never been observed as it is surrounded by a dense disc of gas and dust, opaque to light. This dense disc may be the origin of the hourglass structure of the nebula.

This colour image, which nicely highlights the complex structure of the nebula, is a composite of three exposures through blue, green and red filters. It was made using the 1.5-metre Danish telescope at the ESO La Silla Observatory, Chile.

9 February 2009

Beautiful Sky over Paranal *

This image, taken an early morning two weeks ago, shows with great clarity the amazing sky over Paranal, the home of ESO’s Very Large Telescope (VLT) in Chile.

The wonderful landscape of the Milky Way hangs in all its glory above three of the four 1.8-metre VLT Auxiliary Telescopes (ATs). They observe simultaneously, using interferometry to get a vision as sharp as if they used a telescope with a diameter equal to the largest distance between the telescopes, in this case, 48 metres. Because the larger 8.2-metre Unit Telescopes of the VLT are usually used individually, the four ATs have been added to the system to make full use of the interferometric laboratory.

Facing the East, the remarkable photo shows the constellations Ophiuchus (the ‘snake-holder’), Sagittarius (the ‘archer’), Scorpius (the ‘scorpion’), and Triangulum Australe (the ‘southern triangle’). The Centre of the Milky Way is just below the centre of the image.

This image is available as a mounted image in the ESOshop.

2 February 2009

Ballet of Interacting Galaxies

The pair of galaxies NGC 1531/2, engaged in a spirited waltz, is located about 70 million light-years away towards the southern constellation Eridanus (The River). The deformed foreground spiral galaxy laced with dust lanes NGC 1532 is so close to its companion — the background galaxy with a bright core just above the centre of NGC 1532 — that it gets distorted: one of its spiral arms is warped and plumes of dust and gas are visible above its disc. The cosmic dance leads to another dramatic effect: a whole new generation of massive stars were born in NGC 1532 because of the interaction. They are visible as the purple objects in the spiral arms.

This exquisite image was made using the 1.5-metre Danish telescope at the ESO La Silla Observatory, Chile. It is based on data obtained through three different filters: B, V and R. The field of view is 12 x 12 arcmin.

26 January 2009

Cleaning a VLT mirror

The 8.2m diameter main mirror of Antu, the first Unit Telescope of ESO's Very Large Telescope, is being cleaned using carbon dioxide snow.

While the telescope enclosure is maintained extremely clean, the mirrors are exposed to the elements during the observations. Consequently, dust from the desert slowly accumulates over the surface of the mirror, making it less reflective over time.

The mirror's surface is so delicate that normal cleaners used for household mirrors are not appropriate for telescopes. Observatories have developed other methods, such as this one using carbon dioxide snow. The tiny CO2 snowflakes in the white plume have a temperature of almost minus 80 degrees Celsius; when they land on the mirror, which is at room temperature, they cause minuscule 'explosions' that detach the dust grains from the surface. The dust then floats away, leaving the mirror clean. The process is nevertheless very delicate: should Alain Gilliotte, the optician performing the cleaning, let the CO2 device touch the mirror, the fragile reflective Aluminium coating would be scratched. Also, hair or cloth lint should stay away from the mirror, which is why the optician is wearing a white suit made of special plastic. 

12 January 2009

The Trapezium Cluster

The Orion Nebula is arguably the finest of all nebulae within the Milky Way visible from the Northern Hemisphere. With a gaseous repository of 10,000 suns, and illuminated by a cluster of hot young stars, the clouds of Messier 42 — as it is also known — glow with fantastic colours and shapes, giving us a bird’s eye view of one of the greatest star forming nurseries in our part of the Milky Way. Messier 42 is a complex of glowing gas, mostly hydrogen but also helium, carbon, nitrogen, and oxygen in decreasing amounts, located 1,500 light-years away. At its very heart, we find the Trapezium, a group of four very hot stars that illuminate the nebula. They are the brightest of an extended cluster of several thousand young stars many of which lie unseen within the opaque gas and dust. Amazingly, whilst the Orion Nebula is easy to identify with the unaided eye, there is apparently no written record of its existence before the 17th century.

This image is based on data acquired with the 1.5 m Danish telescope at the ESO La Silla Observatory in Chile, through three filters (B: 60 s, V: 30 s, R: 21 s). East is at the upper right corner and North is at the lower right. 

15 December 2008

Spiral Galaxy NGC 1232

The striking, large spiral galaxy NGC 1232, and its distorted companion shaped like the greek letter "theta".

The pair is located roughly 70 million light-years away in the constellation Eridanus (The River). Billions of stars and dark dust are caught up in this beautiful gravitational swirl. The blue spiral arms with their many young stars and star-forming regions make a striking contrast with the yellow-reddish core of older stars.

This image is based on data acquired with the 1.5 m Danish telescope at the ESO La Silla Observatory in Chile, through three filters (B: 900 s, V: 400 s, R: 400 s). East is up, North is to the left.

8 December 2008

ESO helps school to get a bus

About a year ago, ESO kindly agreed to donate a surplus van to the Colegio Hellen Keller, a school for children with visual disabilities, located in Santiago, Chile. The school was in desperate need of some form of transport as there were many children who could either not attend school at all, or had to spend the weekdays away from their family, simply because they could not make the daily journey on public transport, due to their disabilities. The initial idea was to donate one of the bus used to carry staff to Paranal. However, it became clear that this big van was not ideal for the school, especially with rising fuel prices. ESO kindly offered to donate the proceeds from the sale of the van instead, which was in excess of 4.000.000 Chilean Pesos (about 5,000 EUR). The school set up a fund to raise the rest of the money needed to purchase a brand new bus and recently took delivery after a lot of hard work from many fundraisers. As you can see from attached photo, the kids were delighted!

1 December 2008

SN2008bk: The last moments of a star

Supernova 2008bk in the spiral galaxy NGC 7793 was discovered at the end of March 2008 by amateur astronomer Berto Monard from South Africa. The galaxy is 13 million light-years away in the direction of Sculptor constellation. This supernova is a typical example of a massive star that exploded at the end of its life. But this time, the astronomers were able not only to see the explosion, but to precisely pinpoint the star that exploded, a rather rare achievement.

This was made possible because the explosion site had been observed several times with the help of ESO's Very Large Telescope, the latest images having been observed only a few months before the explosion with the new HAWK-I instrument.

An European team of astronomers, led by Seppo Mattila of University of Turku, Finland, then observed the explosion site again two months after the supernova's discovery, this time with the VLT's NACO instrument, which uses adaptive optics to resolve the finest details. Adaptive optics is a technique that allows astronomers to overcome the blurring effect of the atmosphere, thereby producing very sharp images. By comparing these sets of images, the team found the doomed star from the early images.

The colours and brightness of the star revealed it to belong to the family of red supergiants — to which the very bright star Betelgeuse also belongs — and that it had initially a mass of about eight to nine times the mass of our Sun.

Just before exploding, it was about 500 times larger than our Sun, meaning that if it were placed where the Sun is, it would engulf all the planets up to the planet Mars.

This is only the fifth time astronomers have been able to directly trace back the star that exploded as a supernova. Of all these red supergiants, four of them have about eight times the mass of our Sun, which is thought to be the minimum mass needed to produce such explosions.

This research appears today in print as a Letter to the Editor of the Astrophysical Journal (ApJ, 2008, vol. 688, L91). The team is composed of S. Mattila (Tuorla Observatory, University of Turku, Finland), S. Smartt and Mark Crockett (Queen's University Belfast, UK), J. Eldridge (University of Cambridge, UK), J. Maund (University of Copenhagen, Denmark), and J. Danziger (Universita di Trieste, Italy). 

The image shows the star before it exploded (left), as observed with ISAAC and FORS on ESO's Very Large Telescope, and after the explosion (right), as seen by the very sharp NACO.

25 November 2008

Sunset over Paranal Panorama *

Le Very Large Telescope (VLT) on the 2600-metre-high Cerro Paranal is ESOs premier site for observations in the visible and infrared light. It is located in the Chilean Atacama desert. All four unit telescopes of 8.2-metre diameter are individually in operation with a large collection of instruments and have already made amazing scientific discoveries.

The VLT offers also the possibility of combining coherently the light from the four UTs to work as an interferometer. The Very Large Telescope Interferometer (VLTI), with its own suite of instruments, ultimately providing imagery at the milli-arcsecond level as well as astrometry at 10 micro-arcsecond precision. In addition to the 8.2-metre diameter telescopes, the VLTI is complemented with four Auxiliary Telescopes (AT) of 1.8-metre diameter to improve its imaging capabilities and enable full nighttime use on a year-round basis.

The enclosure of the yet to come VLT Survey Telescope (2.6-metre diameter) is visible in the centre of the panorama.

11 November 2008

The Carina Nebula

The Carina Nebula is a large bright nebula that surrounds several clusters of stars. It contains two of the most massive and luminous stars in our Milky Way galaxy, Eta Carinae and HD 93129A. Located 7500 light years away, the nebula itself spans some 260 light years across, about 7 times the size of the Orion Nebula, and is shown in all its glory in this mosaic. It is based on images collected with the 1.5-m Danish telescope at ESO's La Silla Observatory.

Being brighter than one million Suns, Eta Carinae (the brightest star in this image) is the most luminous star known in the Galaxy, and has most likely a mass over 100 times that of the Sun. It is the closest example of a luminous blue variable, the last phase in the life of a very massive star before it explodes in a fiery supernova. Eta Carinae is surrounded by an expanding bipolar cloud of dust and gas known as the Homunculus ('little man' in Latin), which astronomers believe was expelled from the star during a great outburst seen in 1843.

4 November 2008

Gone with the Wind

M1-67 is the youngest wind-nebula around a Wolf-Rayet star, called WR124, in our Galaxy. These Wolf-Rayet stars start their lives with dozens of times the mass of our Sun, but loose most of it through a powerful wind, which is ultimately responsible for the formation of the nebula.

Ten years ago, Hubble Space Telescope observations revealed a wealth of small knots and substructures inside the nebula. The same team, led by Cédric Foellmi (ESO), has now used ESO's Very Large Telescope (VLT) to watch how these structures have evolved and what they can teach us about stellar winds, their chemistry, and how they mix with the surrounding interstellar medium, before the star will eventually blow everything away in a fiery supernova explosion.

The image is based on FORS1 data obtained by the Paranal Science team with the VLT through 2 wide (B and V) and 3 narrow-band filters.

30 September 2008

Milky Way above Paranal

A night of work for the Paranal Observatory, in the Chilean Atacama Desert. This picture, taken on 20 September, shows the incredible beauty of the night sky above the most advanced telescope in the world, ESO's Very Large Telescope. The Milky Way is clearly seen in this superb image. 

22 September 2008

Magnificent Spiral Galaxy NGC 7424

Composite colour-coded image of another magnificent spiral galaxy, NGC 7424, at a distance of 40 million light-years. It is based on images obtained with the multi-mode VIMOS instrument on the ESO Very Large Telescope (VLT) in three different wavelength bands. The image covers 6.5 x 7.2 square arcminutes on the sky. North is up and East is to the right.

Read more about this superb object in the ESO Press Release eso0436.

21 August 2008

The Globular Cluster NGC 3201

Colour-composite image of the globular cluster NGC 3201, obtained with the WFI instrument on the ESO/MPG 2.2-m telescope at La Silla. Globular clusters are large aggregates of stars, that can contain up to millions of stars. They are among the oldest objects observed in the Universe and were presumably formed at about the same time as the Milky Way Galaxy, in the early phase after the Big Bang. This particular globular cluster is located about 16 000 light-years away towards the Southern Vela constellation. The data were obtained as part of the ESO Imaging Survey (EIS), a public survey being carried out by ESO and member states, in preparation for the VLT First Light.

The original image and astronomical data can be retrieved from the EIS Pre-Flames Survey Data Release pages, where many other nice images are also available. 

14 August 2008

The centre of the Milky Way

The centre of our Milky Way galaxy is located in the southern constellation Sagittarius (The Archer) and is "only" 26,000 light-years away. On high-resolution images, it is possible to discern thousands of individual stars within the central, one light-year wide region.

Using the motions of these stars to probe the gravitational field, observations over the last decade have shown that a mass of about 3 million times that of the Sun is concentrated within a radius of only 10 light-days of the compact radio and X-ray source SgrA* (Sagittarius A) at the centre of the star cluster. This means that SgrA* is the most likely counterpart of the black hole believed to exist at the centre of our Galaxy.

This image was obtained in mid-2002 with the NACO instrument at the 8.2-m VLT Yepun telescope. It combines frames in three infrared wavebands between 1.6 and 3.5 µm. The compact objects are stars and their colours indicate their temperature (blue ="hot", red ="cool"). There is also diffuse infrared emission from interstellar dust between the stars. 

A newer image of that region has been published in 2008; see image eso0846a.

7 August 2008

Paranal in Atacama desert

Paranal, the site of the VLT, was chosen for its unique characteristics: extreme dryness, very low cloud coverage, high altitude, and distant from any source of pollution. This wide-angle shot of the Atacama desert around Paranal, which shows the VLT and, in foreground, VISTA, summarizes it all. Photo taken in November 2007.

30 July 2008

VLT Video Compilation 2008

The "Very Large Telescope Video Collection 2008" features High Definition video material which was obtained in June 2008. For the first time, ESO distributes HD-footage of the world's most advanced ground-based observing facility and provides free access to video sequences of outstanding technical quality and beauty.

The material has been edited especially for broadcast use, without commentary or music.

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