Starship Asterisk*

Image Credit: ESA/Hubble & NASA, J. Kalirai, A. Milone

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This Picture of the Week depicts the open star cluster NGC 330, which lies around 180,000 light-years away inside the Small Magellanic Cloud. The cluster — which is in the constellation Tucana (The Toucan) — contains a multitude of stars, many of which are scattered across this striking image.

Pictures of the Week from the NASA/ESA Hubble Space Telescope show us something new about the Universe. This image, however, also contains clues about the inner workings of Hubble itself. The criss-cross patterns surrounding the stars in this image — known as diffraction spikes — were created when starlight interacted with the four thin vanes supporting Hubble’s secondary mirror.

As star clusters form from a single primordial cloud of gas and dust, all the stars they contain are roughly the same age. This makes them useful natural laboratories for astronomers to learn how stars form and evolve. This image uses observations from Hubble’s Wide Field Camera 3, and incorporates data from two very different astronomical investigations. The first aimed to understand why stars in star clusters appear to evolve differently from stars elsewhere, a peculiarity first observed by the Hubble Space Telescope. The second aimed to determine how large stars can be before they become doomed to end their lives in cataclysmic supernova explosions.

Image Credit: ESO/Yuri Beletsky (LCO)

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A spectacular lunar halo — known as a 22° halo — formed in the sky above ESO’s La Silla Observatory. The optical phenomenon is a result of moonlight interacting with millions of ice crystals suspended in the atmosphere, forming a ring with an apparent radius of approximately 22° around the moon. It is also known as the “moon ring” or “winter halo”.

While this is a beautiful sight, it creates conditions which are not optimal for astronomical observations. Clouds and the bright light of the moon affect the quality and accuracy of astronomical observations. However, that does not diminish the allure of this ethereal sight, and in fact some stars remain visible. Notably, Sirius, the brightest star in the night sky, can be seen at the top edge of the image, just left of the centre.

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

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A cataclysmic cosmic collision takes centre stage in this Picture of the Week. The image features the interacting galaxy pair IC 1623, which lies around 275 million light-years away in the constellation Cetus (The Whale). The two galaxies are in the final stages of merging, and astronomers expect a powerful inflow of gas to ignite a frenzied burst of star formation in the resulting compact starburst galaxy.

This interacting pair of galaxies is a familiar sight; Hubble captured IC 1623 in 2008 using two filters at optical and infrared wavelengths using the Advanced Camera for Surveys (ACS). This new image incorporates new data from Wide Field Camera 3 (WFC3), and combines observations taken in eight filters spanning infrared to ultraviolet wavelengths to reveal the finer details of IC 1623. Future observations of the galaxy pair with the NASA/ESA/CASA James Webb Space Telescope (JWST) will shed more light on the processes powering extreme star formation in environments such as IC 1623.

Image Credit: ESO/Petr Horálek

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Perched between the cascading arch of the Milky Way and the dark mountainside of La Silla Observatory lies the New Technology Telescope (NTT).

Since 1989 this ESO telescope has observed and taken images of our night sky in exquisite detail. Some of its more recent achievements include: the observation of the merging of two neutron stars; a more detailed insight into the structure of asteroids; the analysis of hundreds of planetary nebulae; and even research into planets in far off solar systems.

Telescopes with larger primary mirrors are able to capture more light. However, a larger mirror’s perfect shape is more difficult to maintain. Astronomers found that with primary mirrors over five metres in diameter, image quality decreased enormously as gravity pulled them out of shape (NTT is 3.5 meters in diameter and was meant as a pioneer project to allow telescopes with larger mirrors to be built). Active optics, an idea that came from ESO engineer Raymond Wilson, means that a thin and deformable primary mirror can be controlled by a primary support system that applies the necessary force to correct for these gravity-induced deformations.

The improvements to ground-based astronomy as a result of this new design were huge. Active optics became the main feature of the NTT, which has since viewed phenomena in the sky in exquisite detail. The telescope’s active optics were soon implemented on the two, segmented, 10-metre telescopes at Keck Observatory in Hawai‘i. The design of this telescope was revolutionary. Advancements are still being made today, implementing similar technology in some of the largest telescopes in the world.

Image Credit: ESA/Hubble & NASA, A. Riess et al

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This image shows the spiral galaxy NGC 3254, observed using Hubble's Wide Field Camera 3 (WFC3). WFC3 has the capacity to observe ultraviolet, visible and near-infrared light, and this image is a composite of observations taken in the visible and infrared. In this image, NGC 3254 looks like a typical spiral galaxy, viewed side-on. However, NGC 3254 has a fascinating secret that it is hiding in plain sight — it is a Seyfert galaxy, meaning that it has an extraordinarily active core, known as an active galactic nucleus, which releases as much energy as the rest of the galaxy put together.

Seyfert galaxies are not rare — about 10% of all galaxies are thought to be Seyfert galaxies. They belong to the class of “active galaxies” — galaxies that have supermassive black holes at their centres that are actively accreting material, which releases vast amounts of radiation as it is accreted. There is a second, far more active, type of active galaxy that is known as a quasar. The active cores of Seyfert galaxies, such as NGC 3254, are brightest when observed in light outside the visible spectrum. At other wavelengths, this image would look very different, with the galaxy’s core shining extremely brightly.

Image Credit: ESO/Petr Horálek

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The dark skies above ESO’s Paranal Observatory, home to ESO’s Very Large Telescope (VLT), yield breathtaking views so clear and so full of stars that you could almost touch them. Standing atop a platform at VLT, ESO Photo Ambassador Petr Horálek reaches towards a standout object in the sky. You may assume this bright body, like many others in the sky, to be a star, but it is in fact a planet in our Solar System: the gas giant Jupiter.

Closer to Earth, the four Unit Telescopes (UTs) that comprise the VLT can be seen in the background. Each UT features an 8.2-metre mirror and they operate synergistically to produce some of the sharpest views of the Universe. Accompanying the four UTs are four smaller, moveable Auxiliary Telescopes (ATs) which have 1.8-metre mirrors.

The Chilean Atacama desert once again proves its value as the ideal location for ESO’s VLT. The remoteness of the observatory means that there is very little to no light pollution, which is vital for astronomy and also yields such breathtaking views.