Starship Asterisk*

Credit: ESA/Hubble & NASA, L. Ho et al

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Few of the Universe’s residents are as iconic as the spiral galaxy. These limelight-hogging celestial objects combine whirling, pinwheeling arms with scatterings of sparkling stars, glowing bursts of gas, and dark, weaving lanes of cosmic dust, creating truly awesome scenes — especially when viewed through a telescope such as the NASA/ESA Hubble Space Telescope. In fact, this image from Hubble frames a perfect spiral specimen: the stunning NGC 2903.

NGC 2903 is located about 30 million light-years away in the constellation of Leo (The Lion), and was studied as part of a Hubble survey of the central regions of roughly 145 nearby disc galaxies. This study aimed to help astronomers better understand the relationship between the black holes that lurk at the cores of galaxies like these, and the rugby-ball-shaped bulge of stars, gas, and dust at the galaxy’s centre — such as that seen in this image.

Credit: ALMA (ESO/NAOJ/NRAO); NRAO/AUI/NSF, B. Saxton

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This is one of 74 nearby galaxies whose stellar nurseries were recently observed by the Atacama Large Millimeter/submillimeter Array, or ALMA, in an astronomical census called Physics at High Angular resolution in Nearby GalaxieS (PHANGS). So far, around 100 000 of these stellar nurseries have been imaged in over 750 hours of observation. ALMA’s remarkable sensitivity provides data at high enough resolution to study these regions in detail, and shows that some are bursting with new stars, while others evolve more gradually.

This anticipated diversity in the process of how stars form was the motivation behind this enormous effort. There have long been theories that aimed to explain how and why these differences might occur, some involving the characteristics of the home galaxy itself — properties such as size, age, and internal dynamics — but our lack of high-resolution data had been an obstacle to testing them.

The vast quantity and variety of data yielded by PHANGS are already helping astronomers to understand more, even though the census is only a third complete. The project aims to observe a total of about 300 000 stellar nurseries and by the end it should significantly advance our understanding of how a galaxy’s properties influence the way in which it forms new stars.

Credit: ESA/Hubble & NASA, F. Ferraro et al

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This sparkling burst of stars is Messier 75. It is a globular cluster: a spherical collection of stars bound together by gravity. Clusters like this orbit around galaxies and typically reside in their outer and less-crowded areas, gathering to form dense communities in the galactic suburbs.

Messier 75 lies in the constellation of Sagittarius (The Archer), around 67 000 light-years away from Earth. The majority of the cluster’s stars, about 400 000 intotal, are found in its core; it is one of the most densely populated clusters ever found, with a phenomenal luminosity of some 180 000 times that of the Sun. No wonder it photographs so well!

Discovered in 1780 by Pierre Méchain, Messier 75 was also observed by Charles Messier and added to his catalogue later that year. This image of Messier 75 was captured by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS).

Credit: ESO/Petr Horálek

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This ESO Picture of the Week, captured by ESO Photo Ambassador Petr Horálek, shows a bright crescent Moon hanging above the Chilean Andes, embedded in a blood-red sky that floods the frame with waves of deep crimson. Also seen here are a couple of the antennas belonging to the Atacama Large Millimeter/submillimeter Array (ALMA), a state-of-the-art observatory that studies light from some of the coldest objects in the Universe.

The silhouetted duo of antennas are seen peering upwards, eager to begin their evening of stargazing — and impatient for the eye-catching ripples of cloud to clear. At an altitude of 5000 metres in the arid Atacama Desert, clouds like these are relatively uncommon. The atmosphere in this region of northern Chile is incredibly dry and regularly leads to clear skies, offering around 300 cloudless nights per year!

ALMA has 66 individual constituent antennas, each of which can be moved very precisely around the vast Chajnantor plateau to create a variety of configurations. When working together they can produce much higher resolution observations of the cosmos than they can individually, and collectively they form the largest ground-based astronomical project in the world.