Starship Asterisk*

Credit: ESA/Hubble & NASA, J. Lee, and PHANGS-HST

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The twisting patterns created by the multiple spiral arms of NGC 2835 create the illusion of an eye. This is a fitting description, as this magnificent galaxy resides near the head of the southern constellation of Hydra, the water snake. This stunning barred spiral galaxy, with a width of just over half that of the Milky Way, is brilliantly featured in this image taken by the NASA/ESA Hubble Space Telescope. Although it cannot be seen in this image, a supermassive black hole with a mass millions of times that of our Sun is known to nestle in the very centre of NGC 2835.

This galaxy was imaged as part of PHANGS-HST, a large galaxy survey with Hubble that aims to study the connections between cold gas and young stars in a variety of galaxies in the local Universe. Within NGC 2835, this cold, dense gas produces large numbers of young stars within large star formation regions. The bright blue areas, commonly observed in the outer spiral arms of many galaxies, show where near-ultraviolet light is being emitted more strongly , indicating recent or ongoing star formation.

Expected to image over 100,000 gas clouds and star-forming regions outside our Milky Way, this survey hopes to uncover and clarify many of the links between cold gas clouds, star formation and the overall shape and morphology of galaxies. This initiative is a collaboration with the international Atacama Large Millimeter/submillimeter Array (ALMA) and the European Southern Observatory's Very Large Telescope's MUSE instrument, through the greater PHANGS program (PI: E. Schinnerer).

The stills above (click for the full view!) represent different time stages in the formation of a close stellar binary from a collapsing cloud of gas. In a recent study, two researchers from Kyushu University in Japan, Yu Saiki and Masahiro Machida, conduct numerical simulations to track the complicated process of a binary’s formation and evolution over ~400 years. In the above frames, the top left panel shows the fragmentation of the gas cloud into two cores roughly 9,000 years after the cloud initially begins to collapse. The succeeding panels show how the separation between these two protostars shrinks over the next several hundred years and disks of gas form around each star and around the binary pair. Saiki and Machida’s simulations also show the high-velocity jets driven from each protostar in the process (see the video below), and how the twin jets tangle on large scales as the stars orbit one another. The characteristics revealed in these simulations neatly reproduce our observations of protobinary systems. For more information, check out the original article linked below the video.

• Astrophysical Journal Letters 897(2):L22 (2020 Jul 10) DOI: 10.3847/2041-8213/ab9d86
• arXiv.org > astro-ph > arXiv:2006.10243 > 18 Jun 2020

Credit: ALMA (ESO/NAOJ/NRAO), L Decin et al (2020 Science)

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The ongoing large-scale ATOMIUM project is being conducted in collaboration with ALMA, the Atacama Large Millimeter/submillimeter Array, which is located in Chile and has ESO as a partner. The project set out to map the stellar winds blowing out from around a dozen red giant stars, an ambitious goal made possible thanks to ALMA’s spectacular resolution. These stellar winds — which are sometimes millions of times stronger than those of our Sun — were expected to be spherical, like the parent stars that they are blasted away from.

However, researchers did not observe spherical stellar winds, but something quite different. As seen in the above image — which shows winds around a star called R Aquilae — the team found that in all cases the stellar winds were not spherical, but had different shapes, including some resembling the delicate petals of a rose. The patterns seen in the stellar winds have a striking resemblance to those of planetary nebulae.

The research team, led by Leen Decin at KULeuven, Belgium, proposed that a process known as binary interaction is responsible for the shape of the stellar winds of red giant stars. As the name suggests, binary interaction involves two objects. The theory is that the stellar winds achieve their shape due to the influence of another star, or a giant planet. Stellar winds are the precursors to planetary nebulae, and the apparent similarity in their structures indicates that the physics that shapes stellar winds also shapes planetary nebulae, and hence that binary interaction is the key agent carving out the planetary nebulae morphologies.

Credit: ESA/Hubble & NASA, R. Tully
Acknowledgement: Gagandeep Anand

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Resting on the tail of the Great Bear in the constellation of Ursa Major, lies NGC 5585, a spiral galaxy that is more than it appears.

The many stars, and dust and gas clouds that make up NGC 5585, shown here in this Hubble image, contribute only a small fraction of the total mass of the galaxy. As in many galaxies, this discrepancy can be explained by the abundant yet seemingly invisible presence of dark matter.

The stellar disc of the galaxy extends over 35 000 light-years across. When compared with galaxies of a similar shape and size, NGC 5585 stands out by having a notably different composition: Contributing to the total mass of the galaxy, it contains a far higher proportion of dark matter.

Hotspots of star formation can be seen along the galaxy’s faint spiral arms. These regions shine a brilliant blue, contrasting strikingly against the ever-black background of space.

Image Credit: Petr Horálek/ESO

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Despite its name, ESO’s Very Large Telescope, the VLT, is not a single telescope! It is in fact made up of an array of four 8.2-metre-diameter Unit Telescopes (UTs) (one of which is shown here) and four additional, movable, 1.8-metre-diameter Auxiliary Telescopes (ATs) (three of which are visible on the right side of this image).

Each UT has its own individual name in the region’s native Mapuche (Mapudungun) language. The star of this image is Antu (or UT1, the first of the UTs), and is pictured here sitting atop Cerro Paranal in Chile. This polychromatic image, taken by ESO Photo Ambassador Petr Horálek, also captures the beautiful colours of the cloudy night sky encircling Antu.

Many night-sky objects are visible here. Starting from the left we see the pink California Nebula, the Pleiades star cluster, the fiery river of the Milky Way, the constellation of Orion and its famous Belt, the looping Gum Nebula, the Carina Nebula and the Southern Cross.

The most curious features are the green bands or stripes to the right of Antu’s enclosure. They are atmospheric gravity waves, generated by storms forming ripples in the greenish layer of Earth’s airglow in the upper atmosphere. This image also appeared in an ESOcast dedicated to Red Sprites, which can occur under similar conditions as gravity waves.

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

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This stunning image by the NASA/ESA Hubble Space Telescope features the spiral galaxy NGC 5643 in the constellation of Lupus (The Wolf). Looking this good isn’t easy; thirty different exposures, for a total of 9 hours observation time, together with the high resolution and clarity of Hubble, were needed to produce an image of such high level of detail and of beauty.

NGC 5643 is about 60 million light-years away from Earth and has been the host of a recent supernova event (not visible in this latest image). This supernova (2017cbv) was a specific type in which a white dwarf steals so much mass from a companion star that it becomes unstable and explodes. The explosion releases significant amounts of energy and lights up that part of the galaxy.

The observation was proposed by Adam Riess, who was awarded a Nobel Laureate in physics 2011 for his contributions to the discovery of the accelerating expansion of the Universe, alongside Saul Perlmutter and Brian Schmidt.

Susanna Kohler wrote:

Yajie Yuan et al., 2020 ApJL

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How could a magnetar — a powerfully magnetized neutron star — produce the brief flashes of radio emission and X-rays we’ve recently spotted from SGR 1935+2154, the first equivalent of a fast radio burst in our own galaxy? Magnetars have crusts that can suddenly crack and shear, shaking the magnetic fields of the star in what’s known as a magnetar quake. Using numerical simulations, a team of scientists led by Yajie Yuan (CCA, Flatiron Institute) has shown that waves from a magnetar quake can propagate to the star’s magnetosphere, converting into blobs of magnetized plasma. These plasmoids accelerate outward from the star, driving blast waves into the surrounding magnetar wind that generate simultaneous X-ray and radio bursts. ...

• Astrophysical Journal Letters 900(2):L21 (2020 Sep 10) DOI: 10.3847/2041-8213/abafa8
• arXiv.org > astro-ph > arXiv:2006.04649 > 05 Jun 2020 (v1), 26 Aug 2020 (v2)