Starship Asterisk*

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

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This image from the NASA/ESA Hubble Space Telescope captures the sparkling globular cluster NGC 6569 in the constellation Sagittarius. Hubble explored the heart of this cluster with both its Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS), revealing a glittering hoard of stars in this astronomical treasure trove.

Globular clusters are stable, tightly bound clusters containing tens of thousands to millions of stars, and are associated with all types of galaxies. The intense gravitational attraction of these closely packed clusters of stars means that globular clusters have a regular spherical shape with a densely populated centre — as can be seen in the heart of this star-studded image.

This observation comes from an investigation of globular clusters which lie close to the centre of the Milky Way. These objects have been avoided in previous surveys, as the dust spread throughout the centre of our galaxy blocks light from these globular clusters and alters the colours of the stars residing in them. The last factor is particularly important for astronomers studying stellar evolution, as the colours of stars can give astronomers insights into their ages, compositions, and temperatures.

The astronomers who proposed these observations combined data from Hubble with data from astronomical archives, allowing them to measure the ages of globular clusters including NGC 6569. Their research also provided insights into the structure and density of globular clusters towards the centre of the Milky Way.

Image Credit: ENEL

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Located on the outskirts of the Chilean Atacama Desert, 600 km north of Santiago and at an altitude of 2400 metres, this seemingly tiny village in the middle of a desert is in fact ESO’s first observatory, the La Silla Observatory.

The many astronomical facilities hosted at La Silla include ESO’s 3.6-metre telescope and ESO’s New Technology Telescope (NTT), as well as several national telescopes, such as ExTrA or the Danish 1.54-metre telescope.

The 3.6-metre telescope started operations in 1977. It is home to the High Accuracy Radial velocity Planet Searcher (HARPS), a powerful exoplanet hunter that discovered Proxima b — an Earth-mass rocky planet orbiting our closest neighbouring star after the Sun.

Inaugurated in 1989, the NTT constituted a major milestone in the field of active optics, a technique that adjusts the shape of a telescope’s mirror against distortions caused by the weight of the mirror itself. Using technology developed at ESO, the NTT was the first telescope in which such corrections were done in real-time during observations.

A village needs power, and La Silla’s photovoltaic plant delivers 1.7 MW using solar panels that stretch over 100 000 square metres in the desert. Thanks to this, all electricity used at the observatory during the day is renewable, preventing the emission of up to 400 tonnes of carbon dioxide equivalent every year. This is part of ESO’s wider efforts to reduce our environmental impact and operate our facilities in a more sustainable way.

Image Credit: ESA/Hubble & NASA, H. Ebeling

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The massive galaxy cluster Abell 1351 is captured in this image by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 and Advanced Camera for Surveys. This galaxy cluster lies in the constellation Ursa Major in the northern hemisphere.

This image is filled with streaks of light, which are actually the images of distant galaxies. The streaks are the result of gravitational lensing, an astrophysical phenomenon that occurs when a massive celestial body such as a galaxy cluster distorts spacetime sufficiently strongly to affect the path of light passing through it — almost as if the light were passing through a gigantic lens. Gravitational lensing comes in two varieties — strong and weak — and both can give astronomers an insight into the distribution of mass within a lensing galaxy cluster such as Abell 1351.

This observation is part of an astronomical album comprising snapshots of some of the most massive galaxy clusters. This menagerie of massive clusters demonstrates interesting astrophysical phenomena such as strong gravitational lensing, as well as showcasing spectacular examples of violent galaxy evolution. To obtain this astronomical album, astronomers proposed a Snapshot Program to be slotted into Hubble’s packed observing schedule. These Snapshot Programs are lists of separate, relatively short exposures which can fit into gaps between longer Hubble observations. Having a large pool of Snapshot candidates to dip into allows Hubble to use every second of observing time possible and to maximise the scientific output of the observatory.

Credit: Gemini Observatory/NOIRLab/NSF/AURA/H. Dottori, R. J. Díaz, G. Gimeno Processing: T.A. Rector (Univ of Alaska Anchorage/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab)

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NGC 7020, a barred lenticular galaxy in the southern constellation Pavo, holds a geometric mystery. Clear but subtle in this image from Gemini South, one half of the International Gemini Observatory, a Program of NSF’s NOIRLab, the core of NGC 7020 is visibly hexagonal in shape. A hexagon is not a common shape for any celestial body, let alone an entire galaxy. To form a hexagonal structure such as this, a considerable number of stars must orbit in a very narrow band. This orbital path includes two denser regions of stars seen on the left and right sides of the hexagon, which are known as “ansae”. NGC 7020’s unusual shape seems to be the product of a very rare orbital resonance, or an as-yet-unknown phenomenon.

The 8-meter Gemini South telescope is located on Cerro Pachón in the Chilean Andes. Along with the other half of the international Gemini observatory, Gemini North in Hawai‘i, these two telescopes give us a deep view of the entire night sky.

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

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This star-studded image shows the globular cluster Terzan 9 in the constellation Sagittarius, towards the centre of the Milky Way. The NASA/ESA Hubble Space Telescope captured this glittering scene using its Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS).

Globular clusters are stable, tightly bound groupings of tens of thousands to millions of stars. As this image demonstrates, the hearts of globular clusters can be densely packed with stars; the night sky in this image is strewn with so many stars that it resembles a sea of sequins or a vast treasure chest crammed with gold.

This starry snapshot is from a Hubble programme investigating globular clusters located towards the heart of the Milky Way. The central region of our home galaxy contains a tightly packed group of stars known as the Galactic bulge, which is also rich in interstellar dust. This dust has made globular clusters near the Galactic centre difficult to study, as it absorbs starlight and can even change the apparent colours of the stars in these clusters. Hubble's sensitivity at both visible and infrared wavelengths has allowed astronomers to measure how the colours of these globular clusters have been changed by interstellar dust, and thereby to establish their ages.

Credit: Gerhard Hüdepohl (atacamaphoto.com)/ESO

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This Picture of the Week shows a soothing sunset over ESO’s Paranal Observatory, home to the Very Large Telescope (VLT). The watercolour skies create a magnificent backdrop for two Auxiliary Telescopes (ATs). The VLT has four of these, and they work together as part of a larger observing facility known as the Very Large Telescope Interferometer (VLTI).

The VLTI combines the cosmic light collected by up to four telescopes, either the ATs or their four larger counterparts, the 8.2 m Unit Telescopes (UTs). A system of mirrors housed within underground tunnels channel the different light beams towards the VLTI lab, where they are combined using a technique called interferometry. This allows researchers to probe the universe with much sharper eyes, with a huge “virtual” telescope as large as the separation between the individual telescopes, currently up to about 140 m, which can spot details that each telescope would individually miss.

The VLTI recently celebrated its 20th birthday With its extraordinarily high resolution, it is able to see fine details such as stellar surfaces, and even to study the stars orbiting the black hole at the centre of our galaxy.