Photo de la semaine

23 octobre 2023: The Great Dimming Event (GDE) of Betelgeuse, where the red supergiant star visibly faded in late 2019 and early 2020, puzzled and fascinated the world as it happened. Some thought that the star, which is coming to the end of its life, was about to explode and go supernova. In this glowing Picture of the Week, astronomers have shed new light on how Betelgeuse became darker, confirming that the GDE wasn’t a precursor to a spectacular supernova after all — sorry! Here we see Betelgeuse as it was in December 2018, February 2020 and December 2020, capturing the famed star before, during, and after the GDE. A team led by Julien Drevon, Florentin Millour and Pierre Cruzalèbes at the Université Côte d’Azur (France) used the MATISSE infrared instrument on ESO’s Very Large Telescope Interferometer (VLTI) to obtain high-resolution images of the star. The top images here show its “surface” or ...

16 octobre 2023: Standing majestically at the top of a hill at ESO’s La Silla Observatory, surveying the watercolour scenery of another sunset in Chile’s Atacama Desert, is the New Technology Telescope (NTT). The star of this Picture of the Week has been ticking along, making discovery after discovery, ever since it was inaugurated in 1989. Its home at La Silla sits at an altitude of 2400 metres and is far from sources of light pollution, giving the NTT uninterrupted views of the Universe. This plucky telescope has a 3.58-metre primary mirror, which it uses to observe the cosmos in optical and near-infrared wavelengths of light. Currently, the NTT is equipped with two instruments: the Son of ISAAC (SOFI) and the ESO Faint Object Spectrograph and Camera 2 (EFOSC2). The former received its unusual name because of its similarity to an instrument on ESO’s Very Large Telescope (VLT, located further north) that went ...

9 octobre 2023: The white pearl on the left side of this Picture of the Week is one of the Exoplanets in Transits and their Atmospheres telescopes — ExTrA for short. Located at ESO’s La Silla Observatory at an altitude of 2375m, ExTrA is a French national project comprising three 60 centimetre telescopes that are working towards one goal: to detect Earth-sized planets in our home galaxy, the Milky Way. ExTrA focuses on planets around very small stars, with a radius down to a tenth of the Sun. It relies on the so-called transit method, looking for slight dips in the light emitted from a star when a planet passes in front of it, like a tiny eclipse. The smaller the star is, the larger the dip an Earth-sized planet will cause. Each telescope observes a target star and four reference ones to calibrate the effects of Earth’s atmosphere. The telescopes can observe ...

2 octobre 2023: There are two different types of nebulae brought to you in this Picture of the Week. Each appears with a distinct colour in the visible sky and are captured here using the wide-field camera OmegaCAM on the VLT Survey Telescope (VST), hosted at ESO’s Paranal Observatory in the Chilean desert. The large, bright emission nebula at the centre, IC1284, is a star-forming region composed primarily of hydrogen. Its rosy glow comes from electrons within the hydrogen atoms: they’re excited by the radiation from young stars, but then they lose energy and emit a specific colour or wavelength of light. One of the filters on OmegaCAM lets through this particular reddish colour, hence the nebula’s look. Meanwhile, another colour filter highlights the blue reflection nebulae NGC6589 and NGC6590 in the lower right corner. The dust in a reflection nebula preferentially scatters shorter, bluer wavelengths of light from nearby stars, which is ...

25 septembre 2023: It’s hard not to get sucked into this Picture of the Week, taken using a long exposure at ESO’s Paranal Observatory in the Chilean Atacama Desert. Above the mountaintop observatory, a spectacular dance is playing out: imaged over several hours, stars appear to make their way in long arcs, called star trails, across the night sky. Paranal is home to one of the world’s most advanced optical telescopes: ESO’s Very Large Telescope, or VLT. This flagship facility actually consists of four Unit Telescopes and four smaller movable Auxiliary Telescopes, like the one in the foreground on the right. But what are those mysterious beams of orange light erupting from one of the Unit Telescopes? Well, they’re for making stars, kind of. The Four Laser Guide Star Facility propagates laser beams[1] into the sky, making sodium atoms in the upper atmosphere glow like artificial stars. Each laser delivers 22 watts of ...

18 septembre 2023: This Picture of the Week shows the unique stellar system HIP 81208, as captured by ESO’s Very Large Telescope (VLT) in Chile. Astronomers thought HIP 81208 was a system consisting of a massive central star (A, the central bright spot), a brown dwarf (B) circling around it, and a low-mass star (C) orbiting further away. However, a new study has revealed a never-before-seen hidden gem: an object (Cb), approximately 15 times more massive than Jupiter, orbiting around the smaller of the two stars (C). The discovery of Cb means that HIP 81208 is a uniquely intriguing system with two stars and two smaller bodies orbiting each one –– in other words, a hierarchical quadruple system. The mass of the newly found Cb object places it right at the border between planets and brown dwarfs –– failed stars that are not massive and hot enough to fuse hydrogen into helium. The ...

11 septembre 2023: There are several galaxies in this Picture of the Week, but the most fascinating is probably the one surrounded by four light-blue dots, resembling a flower with blue petals. But, are these dots real? Yes and no… Taken with ESO’s Very Large Telescope (VLT), this image shows a so-called Einstein Cross. The four ‘petals’ are images of a distant galaxy hidden behind the orange galaxy at the centre. Something very fascinating happens to allow us to detect the light from this hidden object: the galaxy at the centre acts as a gravitational lens, bending the light emitted from the distant galaxy around it. As a result, we see several images of the distant galaxy, distorted and magnified. In the special configuration of these two galaxies, the hidden one appears as four images around the central ‘lens’ galaxy, forming a cross-like (or flower-like) pattern dubbed an Einstein Cross. Gravitational lensing thus ...

4 septembre 2023: It might look like the opening scene from The Lion King, but this stunning Picture of the Week was actually taken in the Chilean Atacama Desert rather than the African savannas. Taking centre stage is ESO’s Extremely Large Telescope (ELT), or part of it, at least. The ELT’s steel dome is about 80 metres tall and one day it will play host to the world’s biggest eye on the sky. When finished, the dome will weigh some 6100 tonnes and be capable of rotating 360 degrees on a set of 36 stationary trolleys. This spectacular photograph of the sunrise over Cerro Armazones, the ELT’s perch, was shot on 29 August from around 23 kilometres away on top of another famous mountain: Cerro Paranal, home to the ELT’s older sibling, ESO’s Very Large Telescope, or VLT. You could say the stars were aligned for this image: since the position of the ...

28 août 2023: The flat panorama of the Chajnantor plateau dominates this Picture of the Week. Situated at an altitude of around 5000 metres in the Chilean Andes, this plateau is one of the driest places on Earth — challenging for humans, but perfect for astronomical observations. This breathtaking landscape is home to the Atacama Pathfinder Experiment (APEX), the white structure down in the centre of the image. Inaugurated in 2005, APEX is a 12-metre diameter radio telescope that studies the cold, dusty and distant Universe, and is operated by ESO on behalf of the Max Planck Institute for Radio Astronomy (MPIfR). Now look ahead, towards the distant brown mountains, and you might be able to make out a bunch of white dots. Those are in fact the 66 high-precision antennas of ALMA, the Atacama Large Millimeter/submillimeter Array, operated by ESO together with its international partners. Like APEX, ALMA’s antennas observe the coldest ...

21 août 2023: Welcome to ESO’s La Silla Observatory, home to several telescopes since the 1960s and the setting of this Picture of the Week. Located 600 km north of Chile’s capital Santiago, La Silla sits at around 2400 meters above sea level. More than just the telescopes live at this idyllic location: the staff who run them do too. Astronomers, engineers and support staff spend shifts of several days working on-site, and the buildings in the foreground allow them to live, work and relax in the harsh conditions of the Atacama desert. The building at the centre contains bedrooms, a canteen, a gym and a cinema room, among other facilities. On the left we can see dormitories where visiting astronomers can rest after a long night observing the cosmos. Meanwhile, the long white building right at the bottom is the New Operations Building, from which the New Technology Telescope (NTT), ESO 3.6-metre ...

14 août 2023: This Picture of the Week — taken with ESO’s Visible and Infrared Survey Telescope (VISTA) at Paranal Observatory in Chile — might look like a scene from a snowy winter's night, but it’s not. It’s an infrared image of NGC 6723, a globular cluster located about 28 000 light years from Earth in the constellation Sagittarius. Globular clusters are spherical-shaped groups of stars, tightly bound together by gravity. Their name is derived from the Latin word globulus, meaning small sphere — somewhat misleading given that NGC 6723, as most globular clusters, contains hundred of thousands to millions of stars. So far, astronomers have found more than 150 globular clusters in our galaxy, the Milky Way, with most of them estimated to be at least 10 billion years old and hosting some of the oldest stars in the galaxy. Globular clusters were key to pinpointing our own location within the Milky ...

7 août 2023: It’s now close to 80 metres high — the mammoth steel structure of the ESO’s Extremely Large Telescope (ELT) dome is taking shape in this Picture of the Week, taken on 2 August 2023 under the light of the full Moon. Right now, engineers and construction workers are assembling the structure of the telescope dome in the Chilean Atacama Desert, with progress visible almost every day. When completed, the ELT will be the world’s biggest eye on the sky for visible and infrared observations. Overall, the ELT project is now more than 50 percent complete. The dome structure visible here will house a pioneering five-mirror optical design, which includes a giant main mirror (M1), 39 metres wide and made up of 798 hexagonal segments. The telescope mirrors and other components are being built by companies in Europe, where work is progressing well too. All of the other systems needed to ...

31 juillet 2023: Can you see ESO’s New Technology Telescope (NTT) peaking out of its enclosure on the right of this Picture of the Week? When this telescope was inaugurated in 1989 it packed innovative technology that laid the foundations for all ground-based telescopes that would follow. The mirrors of professional telescopes are so large and heavy that they bend under their own weight; if left uncorrected, this would yield distorted images. The NTT, which is located at ESO’s La Silla Observatory in Chile, has a flexible main mirror that can change shape during observations. Using a so-called ‘reference star’, the NTT adjusts the mirror's shape to correct these deformations, thus ensuring optimal image quality. This technique, called active optics (not to be confused with adaptive optics) was developed by the late Raymond Wilson at ESO. Today, it is applied to all major modern telescopes, including ESO’s Very Large Telescope (VLT) at Cerro ...

24 juillet 2023: Imaginez que vous regardiez par le judas de votre porte et que vous voyiez ceci ! Cette image de la semaine montre une vue fisheye du télescope de 1,52 mètre de l'Observatoire de La Silla de l'ESO au Chili, l'un de nos premiers télescopes qui connaît aujourd'hui une seconde vie. L'ESO a été fondé en 1962 et, quelques années plus tard, le télescope de 1,52 mètre a été inauguré. Ce télescope était équipé de plusieurs spectrographes tels que Boller & Chivens, ECHELEC et FEROS, qui ont permis d'étudier, entre autres, des comètes spectaculaires, des étoiles aux vents puissants et des exoplanètes fascinantes. Ce télescope pionnier a été mis hors service en 2002, et FEROS a été transféré au télescope MPG/ESO de 2,2 mètres, également à La Silla, où il continue à rechercher de nouveaux mondes lointains. Mais ce n'était pas la fin du télescope de 1,52 mètre. Après un arrêt ...

17 juillet 2023: Can you see the chameleon in this picture? No? Well, it's camouflaged! Yes, we are joking, but this Picture of the Week actually shows the Chamaeleon Cloud, or IC 2631. In the southern hemisphere, this cloud is visible in the sky for most of the year, and in this image, captured by ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA), you can admire it in infrared light. IC 2631 is a reflection nebula made of dust clouds that reflect the light emitted from nearby stars. The nebula is mainly illuminated by one of the youngest, most massive and brightest stars in its neighborhood, HD 97300, visible to the centre-right of the image. The Chamaeleon Cloud is in fact the brightest nebula in the Chamaeleon Complex, a vast region of gas and dust clouds –– much larger than what this image shows –– where numerous newborn and still-forming stars live. ...

10 juillet 2023: This Picture of the Week shows a beautiful flock of sheep, grazing in the Chilean Andes. No, wait, wait, wait. There's no grass to feed on here, and they are at an altitude of around 5000 metres. Ok, no, they are not sheep. Let’s start again. This Picture of the Week shows the beautiful antennas of the Atacama Large Millimeter/submillimeter Array (ALMA), operated by ESO and its international partners in the Chilean Andes. Ok, that’s better! As you can see, ALMA’s 66 white antennas are not the same size: most of them are 12-metre antennas, and only twelve are 7-metre antennas (see the smaller ones over to the left of the ‘flock’?). They work together as an interferometer, acting like a single big telescope. ALMA observes the light emitted from some of the coldest objects in the Universe, such as the most distant galaxies. These antennas can be physically moved ...

3 juillet 2023: Have you ever seen so many telescopes all together? This Picture of the Week was taken at sunset at ESO’s La Silla Observatory, suspended over an ocean of mountains and soft, foggy clouds. Nestled in the Chilean Atacama Desert at an altitude of 2400 metres, La Silla is far from sources of light pollution and has one of the darkest skies on Earth, which explains why it's packed full with telescopes! How many can you spot here? Let’s take a closer look at a few of them. Almost at the centre of the frame, ESO’s 3.6-metre telescope stands out, with the smaller dome of the Coudé Auxiliary Telescope attached to it. The 3.6 m telescope is home to one of the world’s best extrasolar planet hunters, the so-called High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. The antenna to the left side of the picture is the Swedish-ESO Submillimetre Telescope ...

26 juin 2023: Take a look at this aerial photo of the Atacama Pathfinder Experiment, or APEX for short, sat stoically atop the Chajnator plateau in Chile’s Atacama Desert. This remote, dry location, some 5100 metres above sea level, is the perfect location to uncover the secrets of the so-called “cold universe”, the regions in space only a few tens of degrees above absolute zero. APEX is a 12-metre telescope hosted and operated by ESO on behalf of the Max Planck Institute for Radio Astronomy (MPIfR). It observes at millimetre and submillimetre wavelengths — between infrared and radio waves — where vast cold clouds of interstellar dust and gas glow. These clouds act as the birthplace for new stars and would be obscured in the visible light range. Light collected by APEX is then recorded by different instruments. One of these, known as the Large APEX Bolometer Camera (LABOCA), has an array of ...

19 juin 2023: In Chile’s Atacama desert, ESO’s very own colosseum — the Extremely Large Telescope, or ELT –– is being assembled. As this image taken in early June 2023 shows, progress is moving quickly on the construction site, as the steel frame of the telescope’s dome is pieced together. Parts of the steel backbone running around the edge of the building are fitted together at the ELT base camp before being transported to the platform atop Cerro Armazones using specialised transporters. Not an easy feat given that these pre-assembled steel blocks weigh some 70 tonnes! Once they’re on location, the giant steel Lego-like blocks are hoisted up using the gigantic cranes you see here, and mounted on a rail inserted into trolleys. The entire dome, which will weigh 6,100 tonnes, will rotate on these trolleys when the ELT enters operation. If you peer into the distance, to the right of the yellow ...

12 juin 2023: It might look like there’s not a lot going on in this Picture of the Week, but looks can be deceiving. Far off in the distance, huddled together like penguins in an Antarctic storm, sit the 66 high-precision antennas of the Atacama Large Millimeter/submillimeter Array (ALMA). Operated by ESO together with international partners, ALMA is designed to study the light emitted by the coldest objects in the Universe, such as vast cold clouds in interstellar space. Stretching out either side of the antennas is the empty landscape of the Chajnantor plateau. Sitting at 5,000 m above sea level in the Chilean Andes, this remote location is one of the driest places on Earth. It’s this dryness that makes it the perfect place for observing the signals from the cold Universe which would otherwise be heavily absorbed by water vapour in our atmosphere. ALMA is what’s known as an interferometer, meaning ...