Starship Asterisk*

[c][attachment=0]potw1622a[1].jpg[/attachment]Credit: ESA/Hubble & NASA;
Acknowledgement: Judy Schmidt[/c][hr][/hr]

This 10.5-billion-year-old globular cluster, NGC 6496, is home to heavy-metal stars of a celestial kind! The stars comprising this spectacular spherical cluster are enriched with much higher proportions of metals — elements heavier than hydrogen and helium, are in astronomy curiously known as metals — than stars found in similar clusters.

A handful of these high-metallicity stars are also variable stars, meaning that their brightness fluctuates over time. NGC 6496 hosts a selection of long-period variables — giant pulsating stars whose brightness can take up to, and even over, a thousand days to change — and short-period eclipsing binaries, which dim when eclipsed by a stellar companion.

The nature of the variability of these stars can reveal important information about their mass, radius, luminosity, temperature, composition, and evolution, providing astronomers with measurements that would be difficult or even impossible to obtain through other methods.

NGC 6496 was discovered in 1826 by Scottish astronomer James Dunlop. The cluster resides at about 35 000 light-years away in the southern constellation of Scorpius (The Scorpion).

[img3="Credit: Jaime Guarda/ESO"]https://cdn.eso.org/images/thumb700x/potw1622a.jpg[/img3][hr][/hr]

High upon the Chajnantor Plateau, a solitary vicuña — a relative of llamas, alpacas and camels — stands before the APEX antenna.

Both the animal and the antenna are well-equipped to handle the harshness of their remote and arid environment. At Chajnantor, some 5000 metres above sea level, temperatures can get fairly warm during the day, thanks to the intense sunlight beaming through the thin atmosphere. However, at night, the mercury plunges.

Engineers built the antenna of APEX to withstand the harsh weather, carefully crafting them to endure relentless sunlight, strong winds, and severe temperature changes ranging from +20 to -20 degrees Celsius.

The hardy vicuña, meanwhile, with its thick, wooly coat that traps hot air close to its body, can also handle nature’s quirks. The species, only found at high altitudes in the Andes Mountains, grazes on the tough grasses found across the otherwise barren slopes. Although the Chajnantor region is one of the driest places on the planet, at times the temperature swings can even bring snow to the plateau, an occurrence that the vicuña in this image is investigating!

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With this pane of 16 Forever stamps, the Postal Service showcases some of the more visually compelling historic, full-disk images of the planets obtained during the last half-century of NASA space exploration. Eight new colorful Forever stamps – each shown twice – feature Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Click for full resolution. Credits: USPS/Antonio Alcalá © 2016 USPS

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The souvenir sheet of four New Horizons stamps features two new stamps appearing twice. The first stamp is an artist’s rendering of NASA’s New Horizons spacecraft based on artwork created by APL’s Steve Gribben, while the second stamp shows an enhanced color image of Pluto taken by New Horizons near its closest approach to Pluto. Click for full resolution. Credits: USPS/Antonio Alcalá © 2016 USPS

[img3="Credit: ESA/Hubble & NASA
Acknowledgement: Judy Schmidt"]http://cdn.spacetelescope.org/archives/ ... w1621a.jpg[/img3][hr][/hr]

Nearly as deep as the Hubble Ultra Deep Field, which contains approximately 10 000 galaxies, this incredible image from the NASA/ESA Space Telescope reveals thousands of colourful galaxies in the constellation of Leo (The Lion). This vibrant view of the early Universe was captured as part of the Frontier Fields campaign, which aims to investigate galaxy clusters in more detail than ever before, and to explore some of the most distant galaxies in the Universe.

Galaxy clusters are massive. They can have a tremendous impact on their surroundings, with their immense gravity warping and amplifying the light from more distant objects. This phenomenon, known as gravitational lensing, can help astronomers to see galaxies that would otherwise be too faint, aiding our hunt for residents of the primordial Universe.

MACS J1149.5+2223 is a galaxy cluster located approximately five billion light-years away. In 2012, it helped astronomers uncover one of the most distant galaxies ever discovered. Light from the young galaxy, magnified 15 times by the galaxy cluster, first shone when our 13.7-billion-year-old Universe was a mere 500 million years old — just 3.6 per cent of its current age! ...

[img3="Credit: ESO/Marino et al."]https://cdn.eso.org/images/screen/potw1621a.jpg[/img3][hr][/hr]

Using 39 of the 66 antennas of the Atacama Large Millimeter / submillimeter Array (ALMA), located 5000 metres up on the Chajnantor plateau in the Chilean Andes, astronomers have been able to detect carbon monoxide (CO) in the disc of debris around an F-type star. Although carbon monoxide is the second most common molecule in the interstellar medium, after molecular hydrogen, this is the first time that CO has been detected around a star of this type. The star, named HD 181327, is a member of the Beta Pictoris moving group, located almost 170 light-years from Earth.

Until now, the presence of CO has been detected only around a few A-type stars, substantially more massive and luminous than HD 181327. Using the superb spatial resolution and sensitivity offered by the ALMA observatory astronomers were now able to capture this stunning ring of smoke and map the density of the CO within the disc.

The study of debris discs is one way to characterise planetary systems and the results of planet formation. The CO gas is found to be co-located with the dust grains in the ring of debris and to have been produced recently. Destructive collisions of icy planetesimals in the disc are possible sources for the continuous replenishment of the CO gas. Collisions in debris discs typically require the icy bodies to be gravitationally perturbed by larger objects in order to reach sufficient collisional velocities. Moreover, the derived CO composition of the icy planetesimals in the disc is consistent with the comets in our Solar System. This possible secondary origin for the CO gas suggests that icy comets could be common around stars similar to our Sun which has strong implications for life suitability in terrestrial exoplanets. ...

• arXiv.org > astro-ph > arXiv:1605.05331 > 17 May 2016