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22 Maggio 2023: A lot can change in more than two decades — just take a look at these pictures of ESO’s Very Large Telescope (VLT)! On the left we see the VLT when it was still under construction atop Cerro Paranal in Chile, while on the right we see it in all its glory as it stands today. Before building the telescopes themselves the mountain had to be lowered by 28 metres to create the telescope platform, which meant removing some 350 000 cubic metres of rock. Then in 1998 the Unit Telescope UT1 (Antu), the leftmost telescope and the furthest along in its construction in the “then” picture, captured its first image of the cosmos — 25 years ago this week. Today, the VLT consists of four Unit Telescopes with main mirrors of 8.2 metres diameter and four movable 1.8-metre diameter Auxiliary Telescopes. After a quarter of a century of observations, ...

15 Maggio 2023: Have you ever seen a sunset so red? Probably not, since the cause of this reddened twilight sky is something quite dramatic: a volcanic eruption. This Picture of the Week was captured at ESO’s Paranal Observatory in Chile; under the Milky Way, on the top of the dark silhouette of Cerro Paranal, ESO’s Very Large Telescope looks upwards to the sky. On 15 January 2022, the submarine volcano Hunga Tonga–Hunga Ha‘apai erupted in the southern Pacific Ocean. This eruption created shock waves that rippled through the atmosphere, reaching places far from the volcano itself. At ESO’s Paranal and La Silla observatories in Chile, more than 10 000 kilometres away, weather stations detected these atmospheric disturbances. The eruption also launched an ash plume 57 kilometres tall, releasing massive quantities of particles into the atmosphere, including water vapour and dust. Sunlight is scattered and reddened by these tiny dust particles, and this ...

08 Maggio 2023: The telescope peeking out from its dome is the 1.52-metre telescope at La Silla Observatory. Being over 55 years old, the 1.52-metre is one of the oldest telescopes at ESO and it has participated in laying the foundation for many areas of astronomical research. Being a special telescope in many ways, it also has a twin, the 1.52-metre telescope at the Observatoire de Haute Provence in France. Both telescopes were specifically designed to do stellar spectroscopy and astrophotography, and the 1.52-m in La Silla involved no less than five instruments, including the B&C spectrograph. This instrument captured the spectrum of the Hale-Bopp comet as it passed by in 1995, one of the first recorded spectrums of a comet. After over 30 years of service, the 1.52-m at La Silla was decommissioned in 2002. Still sitting in its dome, it peers out over the vast Atacama Desert, and we get to ...

01 Maggio 2023: In this colorful Picture of the Week we see a portion of the Gum 10 nebula through the eyes of ESO’s Very Large Telescope in Chile. Gum 10 was discovered by the Australian astronomer Colin Stanley Gum, who in 1955 published a catalogue with more than 80 similar diffuse nebulae. The energetic ultraviolet radiation from the hot blue stars in Gum 10 ionise the gas in the nebula, stripping electrons away from their atoms. When these electrons combine again with the atoms, they emit light at very specific colours or wavelengths. The red shade in this image comes from hydrogen, the most abundant element in the Universe. The dark areas are dense clouds of dust that partially block our view of the objects behind them. This image, taken with the FORS2 instrument, was created as part of the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, ...

24 Aprile 2023: This Picture of the Week shows a newly-formed planet with a mass similar to Jupiter’s orbiting the star HD 169142. The star has a disc around it, and as the protoplanet moves it carves a circular gap in the disc, as seen in the first image. But how was this planet found? Astronomers observed the system over several years with the SPHERE instrument at ESO’s Very Large Telescope in Chile. A new re-analysis of this data, led by Iain Hammond from Monash University in Australia, confirmed the presence of this protoplanet, which moves around the star at a distance somewhat larger than that between Neptune and the Sun. They also identified a spiral wake that the protoplanet leaves behind as it rearranges part of the material in the disc, much like a boat can create a wake as it moves through water. A protoplanet forms during the early stages of ...

17 Aprile 2023: This Picture of the Week shows the young stellar object 244-440 in the Orion Nebula observed with ESO’s Very Large Telescope (VLT) –– the sharpest image ever taken of this object. That wiggly magenta structure is a jet of matter launched close to the star, but why does it have that shape? Very young stars are often surrounded by discs of material falling towards the star. Some of this material can be expelled into powerful jets perpendicularly to the disc. The S-shaped jet of 244-440 suggests that what lurks at the center of this object isn’t one but two stars orbiting each other. This orbital motion periodically changes the orientation of the jet, similar to a water sprinkler. Another possibility is that the strong radiation from the other stars in the Orion cloud could be altering the shape of the jet. These observations, presented in a new paper led by ...

10 Aprile 2023: Don’t worry, no planets were harmed in the making of this Picture of the Week! The powerful laser beams seen here are installed in one of the four 8.2-m telescopes of ESO’s Very Large Telescope (VLT) in Chile. They allow astronomers to obtain very sharp images of the cosmos by correcting the blur caused by turbulence in the atmosphere, but how? The lasers are tuned to a very specific colour that excites sodium atoms floating 90 km above the ground, making them glow. This creates artificial “stars” high up in the sky, whose rapid twinkling is monitored in real time by special sensors. Then, instructions are sent to the telescope’s deformable secondary mirror, which quickly reshapes itself to counteract the atmospheric distortion. And all of this happens at millisecond speeds! This technique, known as adaptive optics, can also use real stars as a reference to measure the turbulence. But there ...

03 Aprile 2023: From the long eastward shadows of the telescopes in this Picture of the Week we can see that it’s almost the beginning of a long night shift of stargazing for the telescopes at ESO’s La Silla Observatory. In the foreground of this picture is the BlackGEM array, designed to hunt for the visible light of gravitational wave sources. If you then follow the road up to the summit of La Silla you will pass several ESO telescopes including the 1-metre Schmidt telescope and the New Technology Telescope, until you finally reach the 3.6-metre telescope at the top, home to the HARPS planet hunter. La Silla mountain is ideally situated for an observatory as its isolated location means there is very little light pollution. It is also in Chile’s extremely dry Atacama desert at an altitude of 2400 metres, meaning there’s hardly ever a cloud in the sky and almost every ...

29 Marzo 2023: The circled spot in this Picture of the Week has almost disappeared. What happened? This sequence of images, taken in optical light with ESO’s Very Large Telescope, shows the gamma-ray burst GRB 221009A fading away. Gamma-ray bursts are the most luminous phenomena that we know of in the universe, and GRB 221009A is the brightest one yet as seen from Earth. The burst was detected in October 2022 by several gamma-ray space telescopes, such as NASA's Swift and Fermi and ESA’s INTEGRAL. Then, a few hours after the initial detection, ESO’s X-shooter instrument at the VLT took a spectrum, which provided the first distance measurement to the explosion of approximately 2400 million light years. Thanks to this distance measurement, a team of astronomers led by Daniele Bjørn Malesani (Radboud University, the Netherlands; DAWN/Niels Bohr Institute, Denmark) ruled out an origin in the Milky Way, although the burst is still much ...

20 Marzo 2023: This Picture of the Week shows a beautiful meeting between the Swedish–ESO Submillimetre Telescope (SEST) and the Milky Way, apparently almost touching each other. This shot was taken at ESO’s La Silla Observatory, located on the outskirts of the Chilean Atacama Desert, at an altitude of 2400 metres. Light and darkness shape the Milky Way as it stretches across the night sky. The dark patches are dust clouds blocking the light behind them, coming from millions of stars in the central region of our galaxy. SEST was built on behalf of the Swedish Natural Science Research Council (NFR) and ESO in 1987. It is a 15-m radio telescope, and it was the only large sub-millimetre telescope in the southern hemisphere at the time of first light. In 2003, the telescope was decommissioned as it was superseded by the Atacama Pathfinder EXperiment telescope (APEX) and the Atacama Large Millimeter/submillimeter Array (ALMA) ...

13 Marzo 2023: This picture of the week shows the Sun’s path on the sky as seen from ESO’s Paranal Observatory in Chile. The picture was taken with a pinhole camera with an exposure of 8 months, from 17 April to 11 December 2018. The tall structure in the foreground is the “seeing monitor”, which measures the blur/twinkling of the stars due to the atmospheric turbulence. In the background we can see several domes; the ones to the centre-left are part of the Very Large Telescope, and the rightmost one is the VLT Survey Telescope. But what are those bright coloured lines behind them? They are created by the Sun as it moves in the sky throughout the day, leaving an imprint on the sheet of photographic paper placed inside the pinhole camera. The camera was facing west, so here we see hundreds of sunsets. But as the Earth moves around the Sun, ...

06 Marzo 2023: In this Picture of the Week, we take a deep plunge into the ocean of stars in the IC4701 nebula. This nebula is located in the Sagittarius constellation, and it is twice as wide as the full Moon in the sky. The energetic light from newly-born stars ionizes the hydrogen gas in the nebula, causing it to emit the intense reddish hue seen in this picture. The dark clouds in this image contain large amounts of interstellar dust, too dense for the light of the background stars to pierce through it. The IC4701 nebula is part of a rich and vast complex of dust and gas within which new stars spring to life. When stars are born, most of them are cooler, redder, and less massive than our own Sun. Hotter, more massive stars are much rarer, and they quickly burn through all their fuel and die. This makes these ...

27 Febbraio 2023: In this Picture of the Week, Venus is shining brightly over ESO’s La Silla Observatory in Chile. The picture was taken just before dawn, towards the East, and also features the diffuse zodiacal light –– sunlight scattered by dust particles in the Solar System. The three domes to the left of the road are the BlackGEM telescopes, built by Radboud University, the Netherlands Research School for Astronomy (NOVA), and KU Leuven. BlackGEM will search for the afterglow of some of the most dramatic events in the Universe, such as the collision of black holes and neutron stars. The ripples in space and time generated by these violent events can be detected by the LIGO and Virgo observatories. Thanks to their large field of view, the BlackGEM telescopes can locate the source of visible light from the afterglow of these events, and thereby pinpoint where the collision took place. This allows ...

20 Febbraio 2023: No, you’re not seeing double: this Picture of the Week shows two images of a Jupiter-like planet that orbits the star AF Leporis. The planet has been imaged by two independent groups of astronomers using the SPHERE instrument on ESO’s Very Large Telescope (VLT) in Chile. But why did they target this particular star? The two groups, led by Dino Mesa (INAF, Italy) and Robert De Rosa (ESO, Chile), studied star catalogues from the European Space Agency’s Hipparcos and Gaia satellites. Over the years, these two space missions have accurately pinpointed the position and motion of stars in our galaxy using astrometry. Planets exert a gravitational tug on their host stars, perturbing their trajectory on the sky. The two teams found that the star AF Leporis exhibited such a disturbed trajectory, a telltale sign that a planet could be hiding there. As the two groups took a closer look at ...

13 Febbraio 2023: The Atacama Desert of Chile is one of the driest places on Earth, with extremely reliable weather, making it an excellent site to explore the Universe. So it’s not strange that this is the place ESO has chosen to place the flagship facilities for European ground-based astronomy. At 2635 meters above sea level in the Atacama Desert, we find ESO’s Paranal Observatory, seen on the far mountain top in this image. It hosts several world-class telescopes like the Very Large Telescope (VLT), and the Visible and Infrared Survey Telescope for Astronomy (VISTA), the latter located on its own peak, seen here to the right of the main one. But the desert is good for other astronomy related sciences as well: Mars explorations! The red and rocky environment around Paranal has a strong resemblance to Mars, making it a perfect site for the European Space Agency (ESA) to test their Mars ...

06 Febbraio 2023: Fall deeper into the entrancing NGC 4303, a spiral galaxy located approximately 55 million light-years from Earth in the constellation Virgo. This image combines data taken at radio and visible wavelengths, and is helping astronomers understand how stars form in galaxies. The hypnotising golden glow drawing you into the image corresponds to clouds of molecular gas, the raw material out of which stars form. The data was taken with the Atacama Large Millimeter/submillimeter Array (ALMA), co-operated by ESO in the Chilean Andes. The blueish regions in the background, on the other hand, were imaged with the Multi-Unit Spectroscopic Explorer (MUSE) instrument on ESO’s Very Large Telescope (VLT), also in Chile, and they reveal already formed stars. By comparing the distribution of gas and stars astronomers are able to study what triggers, enhances or hampers the birth of new stars. This image is part of the Physics at High Angular resolution ...

30 Gennaio 2023: This Picture of the Week shows the grand skies of the Chajnantor plateau in the Chilean Atacama desert. The rare sight of clouds in this typically dry and arid region creates a dramatic display of reds and blues, as well as a sun pillar –– an optical phenomenon caused by ice crystals in the atmosphere –– that emanates from the Sun in line with a telescope. This large antenna is a part of the Atacama Large Millimeter/submillimeter Array (ALMA), which is co-owned by ESO. ALMA is one of the most powerful observatories in the world for radio astronomy. Its collection of 66 antennae — like the one pictured above — has been responsible for many incredible ground-breaking discoveries, including contributing to the creation of the first image of a black hole.

23 Gennaio 2023: In this Picture of the Week, a three hour long photographic sequence shows the path of a lunar eclipse over ESO’s Very Large Telescope (VLT) at Paranal, Chile. This eclipse, which took place on 20-21 January 2019, was visible from the Americas. As the Moon moves into the Earth’s shadow, it becomes darker and acquires a red hue. This reddening, which is due to sunlight being scattered by Earth’s atmosphere before reaching the Moon, can be seen in the middle of the trail. This trail, and those of the stars in the background, are due to the Earth’s rotation and are a ubiquitous feature in long exposure photographs of the night sky. The stars above ESO’s telescopes can be seen clearly because of the high altitude at the Paranal mountain and the lack of light pollution from human settlements. But the bright lunar light can still disturb astronomical observations done ...

16 Gennaio 2023: Since 1979, the 1.54-metre Danish telescope at ESO’s La Silla observatory has been unveiling intricate details about our home galaxy. Stretching over the telescope in this image is the Milky Way and its galactic heart, lighting up the night sky in the Chilean desert. The Danish 1.54-m was used in a 15-year long survey published in 2004 to study 14,000 stars in our galaxy, providing the first clues to the turbulent and violent history of the Milky Way. The survey measured the motions of these stars and their distances, as well as their ages and chemical composition. This allowed the creation of a historical map of the Milky Way which revealed a far more complex history of the galaxy than previously expected. The Milky way cruises the Chilean night sky and looks peaceful in this image, but the survey found traces of a much more dynamic activity in the past. ...

10 Gennaio 2023: In this Picture of the Week we peer closer into the galaxy UGC 4211, where astronomers have discovered two supermassive black holes on the verge of merging, separated by just 750 lightyears — the closest to have been found to date using multiple wavelengths and less than half of the previous record. They used ESO’s Very Large Telescope (VLT), the Atacama Large Millimeter/submillimeter Array (ALMA), of which ESO is a partner, and other telescopes to detect the bright light produced as the black holes engulf material in their vicinity. Both of the images shown here were made using data from the MUSE instrument on ESO’s VLT in Chile. The left image shows a classical view of this galaxy, with dust lanes obscuring starlight. The image on the right shows emission from oxygen, nitrogen and hydrogen in blue, green and red respectively. Red indicates areas of star formation, and the bright ...