Starship Asterisk*

Image Credit: ESA/Hubble & NASA, J. Dalcanton

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A dramatic triplet of galaxies takes centre stage in this latest Picture of the Week from the NASA/ESA Hubble Space Telescope, which captures a three-way gravitational tug-of-war between interacting galaxies. This system —known as Arp 195— is featured in the Atlas of Peculiar Galaxies, a list which showcases some of the weirder and more wonderful galaxies in the universe.

Observing time with the Hubble Space Telescope is extremely valuable, so astronomers don't want to waste a second. The schedule for Hubble observations is calculated using a computer algorithm which allows the spacecraft to occasionally gather bonus snapshots of data between longer observations. This image of the clashing triplet of galaxies in Arp 195 is one such snapshot. Extra observations such as these do more than provide spectacular images — they also help to identify promising targets to follow up with telescopes such as the upcoming NASA/ESA/CSA James Webb Space Telescope.

Image Credit: ESO/Ragusa, Spavone et al.

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Space can be a lonely place. But not so for this quartet of galaxies making up HCG 86 and observed here with ESO’s VLT Survey Telescope (VST). The four galaxies located approximately 270 million light years from Earth in the Sagittarius constellation, are seen from Earth as arranged in triangular shape, with three of them on a straight line and one underneath; the bright objects to the right of the elongated galaxy are not part of the quartet.

HCG stands for Hickson Compact Group, and is used to describe groups of four to ten galaxies where members are physically very close to each other. Because of their compactness, such groups are ideal environments to study galactic interactions, which can sometimes lead to galaxies merging with each other.

This image of HCG 86 was taken by a team of astronomers led by Rossella Ragusa of the Istituto Nazionale di Astrofisica in Italy as part of the VST Early-type Galaxy Survey (VEGAS) programme. “With VST we are able to investigate very faint structures in the galaxies' outskirts, which are the relics of past gravitational interactions and merging events,” says Ragusa. In particular, by mapping the light distribution in and around the group’s galaxies in this study, the team concluded that these faint structures are the leftovers of satellite galaxies gobbled by the group approximately seven billion years ago. ...

Image Credit: ESA/Hubble & NASA, A. Newman, M. Akhshik, K. Whitaker

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The centre of this image from the NASA/ESA Hubble Space Telescope is framed by the tell-tale arcs that result from strong gravitational lensing, a striking astronomical phenomenon which can warp, magnify, or even duplicate the appearance of distant galaxies.

Gravitational lensing occurs when light from a distant galaxy is subtly distorted by the gravitational pull of an intervening astronomical object. In this case, the relatively nearby galaxy cluster MACS J0138.0-2155 has lensed a significantly more distant quiescent galaxy — a slumbering giant known as MRG-M0138 which has run out of the gas required to form new stars and is located 10 billion light years away. Astronomers can use gravitational lensing as a natural magnifying glass, allowing them to inspect objects like distant quiescent galaxies which would usually be too difficult for even Hubble to resolve.

This image was made using observations from eight different infrared filters spread across two of Hubble’s most advanced astronomical instruments: the Advanced Camera for Surveys (ACS) and the Wide Field Camera 3 (WFC3). These instruments were installed by astronauts during the final two servicing missions to Hubble, and provide astronomers with superbly detailed observations across a large area of sky and a wide range of wavelengths.

Image Credit: ESO/Petr Horálek

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Planets, the Galactic centre, stars, glowing gas, silhouetted mountains, and even a comet — this Picture of the Week, taken near the main entrance building of ESO’s Paranal Observatory, is aglow with all the splendours of the clear Chilean skies.

On the horizon, a green object shines like a round, fuzzy blob; this is actually an interplanetary visitor called Comet 252P/LINEAR. This comet was pictured as it soared past the Earth in April 2016, skimming some 5.3 million kilometres away from our planet (quite close by cosmic standards!). Although it was too faint to see with the unaided eye, it showed up beautifully in telescopic observations and images such as this one.

Further to the right is another colourful object — a small, pink splash, visible just above the horizon adjacent to the comet. This is the Lagoon Nebula, located approximately 5000 light-years from Earth. It can appear grey to an observer using a small telescope or binoculars because the human eye has poor colour sensitivity at low light levels, but in long-exposure photos its fantastically vibrant colours shine through. The most prominent constellation in this window on the sky is Scorpius (The Scorpion), but its stars are easily outshone by the “whitish” planetary giant Saturn, and the red-hued Mars. The rest of the sky is lit up in a palette of soft colours by natural airglow.

The eerily backlit mountain peak on the left of the frame is Cerro Armazones, the peak upon which the Extremely Large Telescope (ELT) is currently under construction. When the ELT sees first light, it will be the world’s biggest eye on the sky, and is expected to make significant advances in the study of exoplanets, supermassive black holes, the early Universe, and the nature of dark energy and dark matter.