Starship Asterisk*

Many stars and galaxies lie on a dark background, in a variety of colours but mostly shades of orange. Some galaxies are large enough to make out spiral arms. Along the bottom of the frame is a large, detailed spiral galaxy seen at an oblique angle, with another galaxy about one-quarter the size just beneath it. Both have a brightly glowing core, and areas of star formation which light up their spiral arms

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Image Credit: ESA/Webb, NASA & CSA, A. Martel

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A crowded field of galaxies throngs this Picture of the Month from the NASA/ESA/CSA James Webb Space Telescope, along with bright stars crowned with Webb’s signature six-pointed diffraction spikes. The large spiral galaxy at the base of this image is accompanied by a profusion of smaller, more distant galaxies which range from fully-fledged spirals to mere bright smudges. Named LEDA 2046648, it is situated a little over a billion light-years from Earth, in the constellation Hercules.

One of Webb’s principle science goals is to observe distant — and hence ancient — galaxies to understand the details of their formation, evolution, and composition. Webb’s keen infrared vision helps the telescope peer back in time, as the light from older, more distant galaxies is redshifted towards infrared wavelengths. Comparing these galactic fossils to modern galaxies will help astronomers understand how galaxies grew to form the structures we see in the universe today. Webb will also probe the chemical composition of thousands of galaxies to shed light on how heavy elements were formed and built up as galaxies evolved.

To take full advantage of Webb’s potential for galaxy archeology, astronomers and engineers must first calibrate the telescope’s instruments and systems. Each of Webb’s instruments contains a labyrinthine array of mirrors and other optical elements that redirect and focus starlight gathered by Webb’s main mirror. This particular observation was part of the commissioning campaign for Webb’s Near-InfraRed Imager and Slitless Spectrograph (NIRISS). As well as performing science in its own right, NIRISS supports parallel observations with Webb’s Near-InfraRed Camera (NIRCam). NIRCam captured this galaxy-studded image while NIRISS was observing the white dwarf WD1657+343, a well-studied star. This allows astronomers to interpret and compare data from the two different instruments, and to characterise the performance of NIRISS.

Wispy, nebulous clouds extend from the lower-left of the image. At the top and right the dark background of space can be seen through the sparse nebula. Along the left and in the corner are many layers of brightly-coloured gas and dark, obscuring dust. A cluster of small, bright blue stars in the same corner expands out across the image. Many much smaller stars cover the background.

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Credit: ESA/Hubble & NASA, C. Murray, E. Sabbi; Acknowledgement: Y.-H. Chu

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A snapshot of the Tarantula Nebula (also known as 30 Doradus) is the most recent Picture of the Week from the NASA/ESA Hubble Space Telescope. The Tarantula Nebula is a large star-forming region of ionised hydrogen gas that lies 161 000 light years from Earth in the Large Magellanic Cloud, and its turbulent clouds of gas and dust can be seen swirling between the region’s bright, newly-formed stars.

The Tarantula Nebula is a familiar site for Hubble. It is the brightest star-forming region in our galactic neighbourhood and home to the hottest, most massive stars known. This makes it a perfect natural laboratory in which to test out theories of star formation and evolution, and a rich variety of Hubble images of this region have been released to the public in recent years. The NASA/ESA/CSA James Webb Space Telescope also recently delved into this region, revealing thousands of never-before-seen young stars.

This new image combines data from two different observing proposals. The first was designed to explore the properties of the dust grains that exist in the void between stars and which make up the dark clouds winding through this image. This proposal, which astronomers named Scylla, complements another Hubble observing proposal called Ulysses and is revealing how interstellar dust interacts with starlight in a variety of environments. This image also incorporates data from an observing programme studying star formation in conditions similar to the early Universe, as well as cataloguing the stars of the Tarantula Nebula for future science with Webb.

C. Duran / ESO / ALMA

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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.

Two very bright stars with cross-shaped diffraction spikes are prominent: the larger is slightly lower-right of centre, the smaller lies towards the upper-left corner. Small red stars with short diffraction spikes are scattered around them. The background is covered nearly completely by gas: smoky, bright blue gas around the larger star in the centre and lower-right, and wispier red gas elsewhere.

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Image Credit: ESA/Hubble & NASA, J. Bally, M. Robberto

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The bright variable star V 372 Orionis takes centre stage in this image from the NASA/ESA Hubble Space Telescope, which has also captured a smaller companion star in the upper left of this image. Both stars lie in the Orion Nebula, a colossal region of star formation roughly 1450 light years from Earth.

V 372 Orionis is a particular type of variable star known as an Orion Variable. These young stars experience some tempestuous moods and growing pains, which are visible to astronomers as irregular variations in luminosity. Orion Variables are often associated with diffuse nebulae, and V 372 Orionis is no exception; the patchy gas and dust of the Orion Nebula pervade this scene.

This image overlays data from two of Hubble’s instruments. Data from the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3) at infrared and visible wavelengths were layered to reveal rich details of this corner of the Orion Nebula. Hubble also left its own subtle signature on this astronomical portrait in the form of the diffraction spikes surrounding the bright stars. These prominent artefacts are created by starlight interacting with Hubble’s inner workings, and as a result they reveal hints of Hubble’s structure. The four spikes surrounding the stars in this image are created by four vanes inside Hubble supporting the telescope’s secondary mirror. The diffraction spikes of the NASA/ESA/CSA James Webb Space Telescope (JWST), on the other hand, are six-pointed as a result of Webb’s hexagonal mirror segments and 3-legged support structure for the secondary mirror.

Image Credit: ESO/J. C. Muñoz-Mateos

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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 in visible light. Astronomers therefore must take into account the position and phase of the Moon when planning and executing observations.

Image Credit: PNO/NOIRLab/NSF/AURA/T. Slovinský

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As the Sun sets and its light scatters through Earth’s atmosphere, the Arizona sky glows in wondrous shades of vivid color. Kitt Peak National Observatory (KPNO), a Program of NSF’s NOIRLab, is the perfect location to enjoy these spectacular sunsets. Arid deserts, like the Arizona-Sonoran Desert where KPNO is located, display a clearer array of colors than areas where rain and humid weather are almost daily features. When heavy particles are present in the atmosphere, like water vapor, they absorb some of the sunlight and desaturate the colors. Through dry desert air, however, sunlight can pass unobstructed as it reaches our eyes. These natural conditions are helped by the clean air and low air pollution that are due to Arizona’s sparse population. For astronomers, the torrid, cleaner air enhances their ability to capture sharper data of the visible sky once the dark sets in.

Image Credit: ESA/Hubble & NASA, R. Tully

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A host of astronomical objects throng this image from the NASA/ESA Hubble Space Telescope. Background galaxies ranging from stately spirals to fuzzy ellipticals are strewn across the image, and bright foreground stars much closer to home are also present, surrounded by diffraction spikes. In the centre of the image, the vague shape of the small galaxy UGC 7983 appears as a hazy cloud of light. UGC 7983 is around 30 million light-years from Earth in the constellation Virgo, and is a dwarf irregular galaxy — a type thought to be similar to the very earliest galaxies in the Universe.

This image also conceals an astronomical interloper. A minor asteroid, only a handful of kilometres across, can be seen streaking across the upper left-hand side of this image. The trail of the asteroid is visible as four streaks of light separated by small gaps. These streaks of light represent the four separate exposures that were combined to create this image, the small gaps between each observation being necessary to change the filters inside Hubble’s Advanced Camera for Surveys (ACS). 

Capturing an asteroid was a fortunate side effect of a larger effort to observe every known galaxy close to the Milky Way. When this project was first proposed, roughly 75% of all the Milky Way’s near galactic neighbours had been imaged by Hubble. A group of astronomers proposed using the gaps between longer Hubble observations to capture images of the remaining 25%. The project was an elegantly efficient way to fill out some gaps not only in Hubble's observing schedule, but also in our knowledge of nearby galaxies.

Image Credit: Zdeněk Bardon/ESO

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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. In particular, collisions with other smaller galaxies brought gigantic gas clouds that made the Milky Way come alive with star-formation and supernova explosions, making it the stunning place that we call home. 

Gemini Observatory/NOIRLab/NSF/AURA/Petr Horálek (Institute of Physics in Opava)

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The extent of our visual field is limited, and can process little information compared to its actual environment. But what would the night sky look like with a much wider field of view, like with a camera?

In this panorama, the Milky Way sets the night ablaze in a bright glowing pillar, dividing the sky in two. On the right, the Gemini South telescope — one half of the International Gemini Observatory, operated by NSF’s NOIRLab — projects its laser guide star into the atmosphere. In the sky above the telescope, from left to right, lie the Small and Large Magellanic Clouds and the star Canopus. On the other end of the image is the SOAR Telescope — part of Cerro Tololo Inter-American Observatory (CTIO), a Program of NOIRLab — with three stars above it forming the semblance of a triangle. The top left vertex is Denebola, the bottom Arcturus, and the top right Spica. There are many more objects in the night sky than these, though it is quite impressive to capture this many with just a panorama. Imagine how much more stunning detail large telescopes like Gemini South and SOAR can discover.

This photo was taken as part of the recent NOIRLab 2022 Photo Expedition to all the NOIRLab sites. A full 360-degree panorama of this image can be viewed here.

Image Credit: ESO/Koss et al.

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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 white central region indicates the presence of two supermassive black holes swallowing material from their surroundings. 

Combining data from the VLT, ALMA and other telescopes, a team led by Michael Koss at Eureka Scientific in the US could identify these two black holes and study them in detail. These black holes likely found each other when their host galaxies collided and merged. Observing this system will help improve our understanding of how galaxies and their supermassive black holes grow as they merge.

• Astrophysical Journal Letters 942(1):L42 (2023 Jan 01) DOI: 10.3847/2041-8213/aca8f0
  arXiv | astro-ph | arXiv:2301.03609 | 09 Jan 2023