Starship Asterisk*

Image Credit: E. Garcés/ESO. Ack: N. Dubost

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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 sunrise changes throughout the year as the Earth moves around the Sun, there’s only a narrow window of time when the sunrise frames the ELT if observed from Paranal.

What’s more, if you look carefully, you can just about make out two sunspots on the Sun’s surface. These dark, cooler regions are formed by intense magnetic fields. While they may look small from this distance, in reality they’re the size of planets.

A spiral galaxy. It is irregularly-shaped and its spiral arms are difficult to distinguish. The edges are faint and the core has a pale yellow glow. It is dotted with small, wispy, blue regions where stars are forming. A few stars and small galaxies in warm colours are visible around it. (Image Credit: ESA/Hubble & NASA, A. Filippenko)

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The swirls of the galaxy IC 1776 stand in splendid isolation in this image from the NASA/ESA Hubble Space Telescope. This galaxy lies over 150 million light-years from Earth in the constellation Pisces.

IC 1776 recently played host to a catastrophically violent explosion — a supernova — which was discovered in 2015 by the Lick Observatory Supernova Search, a robotic telescope which scours the night sky in search of transient phenomena such as supernovae. A network of automatic robotic telescopes are spread across the globe, operated by both professional and amateur astronomers, and, without human intervention, reveal short-lived astronomical phenomena such as wandering asteroids, gravitational microlensing, or supernovae.

Hubble investigated the aftermath of the supernova SN 2015ap during two different observing programmes, both designed to comb through the debris left by supernovae explosions in order to better understand these energetic events. A variety of telescopes automatically follow up the detection of supernovae to obtain early measurements of these events’ brightnesses and spectra. Complementing these measurements with later observations which reveal the lingering energy of supernovae can shed light on the systems which gave rise to these cosmic cataclysms in the first place.

Image Credit: International Gemini Observatory/NOIRLab/AURA/NSF/A. Hara

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Near the summit of Maunakea, Gemini North — the northern half of the International Gemini Observatory operated by NSF’s NOIRLab — sits high above the clouds of Hawai‘i in the company of other Maunakea observatories. Being at an altitude of approximately 4200 meters (nearly 14,000 feet) above sea level allows the telescope to capture amazing views of the world beyond Earth’s atmosphere. In addition, Gemini North’s location also grants it stable weather and atmospheric conditions for many nights a year, giving a perfectly clear picture of the sky. At such a high elevation, clouds often form below the summit to form a cloud deck. As is the case in this image however, there are times when clouds accumulate higher in the sky above these facilities. Of course, a few high clouds will not stop astronomers from using Gemini North to make the most of their observations!

Image Credit: ESO/A. Cikota et al.

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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 ([urlhttps://www.eso.org/public/teles-instr/paranal-observatory/vlt/]VLT[/url]), 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 allows us to discover hidden galaxies that would be otherwise invisible to us.

The observations of this system were conducted with the Multi Unit Spectroscopic Explorer (MUSE) instrument at ESO’s VLT in Chile. MUSE splits the light coming from every point within the area being observed into a rainbow or spectrum, which provides astronomers with a wealth of information about the objects within the field of view. The results of these observations, presented in a new paper led by Aleksandar Cikota at the Gemini Observatory in Chile, show that the distant galaxy is forming stars at a rapid rate. Since light left the galaxy when the Universe was about 20% of its current age, studying it provides clues about how galaxies formed in the early Universe.

• Astrophysical Journal Letters 953(1):L5 (2023 Aug 10) DOI: 10.3847/2041-8213/ace9da
• arXiv > astro-ph > arXiv:2307.12470 > 24 Jul 2023

A large elliptical galaxy. It appears to be formed of faint, grey, concentric ovals that grow progressively brighter towards the core, where there is a very bright point, and fade away at the edge. Two threads of dark red dust cross the galaxy’s disc, near the centre. The background is black and mostly empty, with only a few point stars and small galaxies. (Image Credit: ESA/Hubble & NASA, R. Sharples, S. Kaviraj, W. Keel)

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This dream-like Picture of the Week features the galaxy known as NGC 3156. It is a lenticular galaxy, meaning that it falls somewhere between an elliptical and a spiral galaxy. It lies about 73 million light-years from Earth, in the minor equatorial constellation Sextans.

Sextans is a small constellation that belongs to the Hercules family of constellations. It itself is a constellation with an astronomical theme, being named for the instrument known as the sextant. Sextants are often thought of as navigational instruments that were invented in the 18th century. However, the sextant as an astronomical tool has been around for much longer than that: Islamic scholars developed astronomical sextants many hundreds of years earlier in order to measure angles in the sky. A particularly striking example is the enormous sextant with a radius of 36 metres that was developed by Ulugh Beg of the Timurid dynasty in the fifteenth century, located in Samarkand in present-day Uzbekistan. These early sextants may have been a development of the quadrant, a measuring device proposed by Ptolemy. A sextant, as the name suggests, is shaped like one-sixth of a circle, approximately the shape of the constellation.

Sextants are no longer in use in modern astronomy, having been replaced by instruments that are capable of measuring the positions of stars and astronomical objects much more accurately and precisely. NGC 3156 has been studied in many ways other than determining its precise position — from its cohort of globular clusters, to its relatively recent star formation, to the stars that are being destroyed by the supermassive black hole at its centre.

Image Credit: Rubin Observatory/NOIRLab/NSF/AURA/P. Horálek (Inst of Physics in Opava)

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The bright band of the Milky Way seems to spill from the open dome of the Rubin Auxiliary Telescope (AuxTel) in this image from the recent NOIRLab 2022 Photo Expedition. As well as the spectacular Milky Way, replete with intricate clouds of gas and dust, an amorphous airglow is visible along both horizons.

The AuxTel will take a variety of measurements and calibrations during the operations of Vera C. Rubin Observatory, a Program of NSF’s NOIRLab. These complementary data will be used to understand atmospheric conditions and make scientific observations more accurate as Rubin Observatory conducts its decade-long sky survey. In contrast to the new Simonyi Survey Telescope of Rubin Observatory, the AuxTel was repurposed for use at the observatory, a donation from astronomer Edgar Smith.

Rubin Observatory is a joint initiative of the National Science Foundation and the US Department of Energy (DOE). Once completed, Rubin will be operated jointly by NSF’s NOIRLab and DOE's SLAC National Accelerator Laboratory to carry out the Legacy Survey of Space and Time.

ESO/A. Chomez et al.

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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 hidden giant Cb was spotted when a team of astronomers, led by A. Chomez of the Paris Observatory, re-analysed archival data from the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument installed on the VLT. While many other instruments use indirect methods to hunt for far-flung worlds, SPHERE uses a technique known as direct imaging: what we see here is an actual image of the system. Indeed, this is the first hierarchical quadruple system to be found using direct imaging, which will prove invaluable to understanding how complex systems like this one form and evolve.

• Astronomy & Astrophysics 676:L10 (Aug 2023) DOI: 10.1051/0004-6361/202347044
• arXiv > astro-ph > arXiv:2307.01195 > 03 Jul 2023