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Phoebe water-ice

These maps of Saturn’s moon Phoebe show different views of the water-ice absorption across a model of Phoebe’s surface, revealing the body’s icy-rock nature. At 213 km across, Phoebe is the largest of Saturn’s highly inclined irregular satellites, thought to have been captured long ago from the outer solar system. In a recent publication, scientists Wesley Fraser (Queen’s University Belfast, UK) and Michael Brown (California Institute of Technology) have reanalyzed high-resolution spectral imaging of this moon from Cassini’s flyby to explore the water-ice distribution across Phoebe’s surface. Fraser and Brown use their observations to argue that Phoebe’s surface was once quite water poor; its current water-rich state is a consequence of a violent history of impacts, which dredged up water-rich subsurface material. Impact histories like Phoebe’s may explain why there’s so much variation in the amount of water-ice seen on outer-solar-system bodies: more collisions may mean more water-ice. To learn more about the study (and to see more awesome maps and images of Phoebe’s surface!), check out the article below.

Citation

Wesley C. Fraser and Michael E. Brown 2018 AJ 156 23. doi:10.3847/1538-3881/aac213

Spitzer view of N55

What do molecular clouds look like outside of our own galaxy? See for yourself in the images above and below of N55, a molecular cloud located in the Large Magellanic Cloud (LMC). In a recent study led by Naslim Neelamkodan (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan), a team of scientists explore N55 to determine how its cloud properties differ from clouds within the Milky Way. The image above reveals the distribution of infrared-emitting gas and dust observed in three bands by the Spitzer Space Telescope. Overplotted in cyan are observations from the Atacama Submillimeter Telescope Experiment tracing the clumpy, warm molecular gas. Below, new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the sub-parsec-scale molecular clumps in greater detail, showing the correlation of massive clumps with Spitzer-identified young stellar objects (crosses). The study presented here indicates that this cloud in the LMC is the site of massive star formation, with properties similar to equivalent clouds in the Milky Way. To learn more about the authors’ findings, check out the article linked below.

ALMA view of N55

Citation

Naslim N. et al 2018 ApJ 853 175. doi:10.3847/1538-4357/aaa5b0

thin disk simulation

This image (click for the full view!) shows the density of a turbulent accretion disk in one of the first in-depth, three-dimensional magnetohydrodynamic simulations of a thin disk threaded by a large-scale vertical magnetic field. Accretion disks — which include everything from protoplanetary disks to disks around supermassive black holes — are notoriously challenging to model. Both small-scale turbulence and large-scale magnetic fields are thought to be critical processes governing motions within the disk, accretion of material, and launching of disk outflows — but capturing both of these different scales simultaneously in simulations is very difficult. The image above shows computations by Zhaohuan Zhu (University of Nevada, Las Vegas) and James Stone (Princeton University) that span three orders of magnitude in radius, extend all the way to the pole, and are evolved for more than 1,000 innermost orbits. The behavior the authors find is widely applicable to many different kinds of accretion disk systems. To learn more about their results, check out the original study below.

Citation

Zhaohuan Zhu and James M. Stone 2018 ApJ 857 34. doi:10.3847/1538-4357/aaafc9

J210204

New nebulae are being discovered and classified every day — and this false-color image reveals one of the more recent objects of interest. This nebula, IPHASX J210204.7+471015, was recently imaged by the Andalucia Faint Object Spectrograph and Camera mounted on the 2.5-m Nordic Optical Telescope in La Palma, Spain. J210204 was initially identified as a possible planetary nebula — a remnant left behind at the end of a red giant’s lifetime. Based on the above imaging, however, a team of authors led by Martín Guerrero (Institute of Astrophysics of Andalusia, Spain) is arguing that this shell of glowing gas was instead expelled around a classical nova. In a classical nova eruption, a white dwarf and its binary companion come very close together, and mass transfers to form a thin atmosphere of hydrogen around the white dwarf. When this hydrogen suddenly ignites in runaway fusion, this outer atmosphere can be expelled, forming a short-lived nova remnant — which is what Guerrero and collaborators think we’re seeing with J210204. If so, this nebula can reveal information about the nova that caused it. To find out more about what the authors learned from this nebula, check out the paper below.

Citation

Martín A. Guerrero et al 2018 ApJ 857 80. doi:10.3847/1538-4357/aab669

binary star formation

This still from a simulation captures binary star formation in action. Researchers have long speculated on the processes that lead to clouds of gas and dust breaking up into smaller pieces to form multiple-star systems — but these take place over a large range of scales, making them difficult to simulate. In a new study led by Leonardo Sigalotti (UAM Azcapotzalco, Mexico), researchers have used a smoothed-particle hydrodynamics code to model binary star formation on scales of thousands of AU down to scales as small as ~0.1 AU. In the scene shown above, a collapsing cloud of gas and dust has recently fragmented into two pieces, forming a pair of disks separated by around 200 AU. In addition, we can see that smaller-scale fragmentation is just starting in one of these disks, Disk B. Here, one of the disk’s spiral arms has become unstable and is beginning to condense; it will eventually form another star, producing a hierarchical system: a close binary within the larger-scale binary. Check out the broader process in the four panels below (which show the system as it evolves over time), or visit the paper linked below for more information about what the authors learned.

binary star formation multipanel

Evolution of a collapsed cloud after large-scale fragmentation into a binary protostar: (a) 44.14 kyr, (b) 44.39 kyr, (c) 44.43 kyr, and (d) 44.68 kyr. The insets show magnifications of the binary cores. [Adapted from Sigalotti et al. 2018]

Citation

Leonardo Di G. Sigalotti et al 2018 ApJ 857 40. doi:10.3847/1538-4357/aab619

nanodiamonds

This unique image — which measures only 60 x 80 micrometers across — reveals details in the Kapoeta meteorite, an 11-kg stone that fell in South Sudan in 1942. The sparkle in the image? A cluster of nanodiamonds discovered embedded in the stone in a recent study led by Yassir Abdu (University of Sharjah, United Arab Emirates). Abdu and collaborators showed that these nanodiamonds have similar spectral features to the interiors of dense interstellar clouds — and they don’t show any signs of shock features. This may suggest that the nanodiamonds were formed by condensation of nebular gases early in the history of the solar system. The diamonds were trapped in the surface material of the Kapoeta meteorite’s parent body, thought to be the asteroid Vesta. To read more about the authors’ study, check out the original article below.

Citation

Yassir A. Abdu et al 2018 ApJL 856 L9. doi:10.3847/2041-8213/aab433

sunspot

This image of a sunspot, located in in NOAA AR 12227, was captured in December 2014 by the 0.5-meter Solar Optical Telescope on board the Hinode spacecraft. This image was processed by a team of scientists led by Rahul Yadav (Udaipur Solar Observatory, Physical Research Laboratory Dewali, India) in order to examine the properties of umbral dots: transient, bright features observed in the umbral region (the central, darkest part) of a sunspot. By exploring these dots, Yadav and collaborators learned how their properties relate to the large-scale properties of the sunspots in which they form — for instance, how do the number, intensities, or filling factors of dots relate to the size of a sunspot’s umbra? To find out more about the authors’ results, check out the article below.

sunspot umbral dots

Sunspot in NOAA AR 11921. Left: umbral–penumbral boundary. Center: the isolated umbra from the sunspot. Right: The umbra with locations of umbral dots indicated by yellow plus signs. [Adapted from Yadav et al. 2018]

Citation

Rahul Yadav et al 2018 ApJ 855 8. doi:10.3847/1538-4357/aaaeba

Neptune storm

This remarkable series of images by the Hubble Space Telescope (click for the full view) track a dark vortex — only the fifth ever observed on Neptune — as it evolves in Neptune’s atmosphere. These Hubble images, presented in a recent study led by Michael Wong (University of California, Berkeley), were taken in 2015 September, 2016 May, 2016 October, and 2017 October; the observations have monitored the evolution of the vortex as it has gradually weakened and drifted polewards. Confirmation of the vortex solved a puzzle that arose in 2015, when astronomers spotted an unexplained outburst of cloud activity on Neptune. This outburst was likely a group of bright “companion clouds” that form as air flows over high-pressure dark vortices, causing gases to freeze into methane ice crystals. To learn more about what the authors have since learned by studying this vortex, check out the paper below.

Citation

Michael H. Wong et al 2018 AJ 155 117. doi:10.3847/1538-3881/aaa6d6

RGG 118

BH mass vs. bulge mass

Based on its bulge mass, RGG 118’s black-hole mass is low relative to the scaling relation that holds for more massive galaxies with classical bulges. [Adapted from Baldassare et al. 2017]

In this subtle three-color image by Hubble, the nearby dwarf disk galaxy RGG 118 is revealed (you may need to turn up your screen brightness to see its extent!). This tiny galaxy is noteworthy for hosting the smallest active supermassive black hole — at just 50,000 solar masses — found in a galactic center. In a new study led by Vivienne Baldassare (formerly at University of Michigan and now a NASA Einstein Postdoctoral Fellow at Yale University), a team of scientists has used Hubble to image RGG 118 in detail to explore its morphology. They determine that the active galaxy contains an outer spiral disk surrounding an inner pseudobulge, and they confirm that RGG 118’s black hole is undermassive relative to the relation between black-hole mass and bulge mass that describes traditional galaxies well. This suggests that black holes in disk-dominated galaxies grow more gradually than those in galaxies with classical bulges. To learn more about the authors’ discoveries, check out the paper below.

Citation

Vivienne F. Baldassare et al 2017 ApJ 850 196. doi:10.3847/1538-4357/aa9067

Herbig-Haro Lynds’ Dark Nebula 673

Stunning color astronomical images can often be the motivation for astronomers to continue slogging through countless data files, calculations, and simulations as we seek to understand the mysteries of the universe. But sometimes the stunning images can, themselves, be the source of scientific discovery. This is the case with the below image of Lynds’ Dark Nebula 673, located in the Aquila constellation, that was captured with the Mayall 4-meter telescope at Kitt Peak National Observatory by a team of scientists led by Travis Rector (University of Alaska Anchorage). After creating the image with a novel color-composite imaging method that reveals faint Hα emission (visible in red in both images here), Rector and collaborators identified the presence of a dozen new Herbig-Haro objects — small cloud patches that are caused when material is energetically flung out from newly born stars. The image adapted above shows three of the new objects, HH 1187–89, aligned with two previously known objects, HH 32 and 332 — suggesting they are driven by the same source. For more beautiful images and insight into the authors’ discoveries, check out the article linked below!

Lynds’ Dark Nebula 673

Full view of Lynds’ Dark Nebula 673. Click for the larger view this beautiful composite image deserves! [T.A. Rector (University of Alaska Anchorage) and H. Schweiker (WIYN and NOAO/AURA/NSF)]

Citation

T. A. Rector et al 2018 ApJ 852 13. doi:10.3847/1538-4357/aa9ce1

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