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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

toothbrush cluster

This spectacular composite (click here for the full image) reveals the galaxy cluster 1RXS J0603.3+4214, known as the “Toothbrush cluster” due to the shape of its most prominent radio relic. Featured in a recent publication led by Kamlesh Rajpurohit (Thuringian State Observatory, Germany), this image contains new Very Large Array (VLA) 1.5-GHz observations (red) showing the radio emission within the cluster. This is composited with a Chandra view of the X-ray emitting gas of the cluster (blue) and an optical image of the background from Subaru data. The new deep VLA data — totaling 26 hours of observations — provides a detailed look at the complex structure within the Toothbrush relic, revealing enigmatic filaments and twists (see below). This new data will help us to explore the possible merger history of this cluster, which is theorized to have caused the unusual shapes we see today. For more information, check out the original article linked below.

VLA Toothbrush

High resolution VLA 1–2 GHz image of the Toothbrush showing the complex, often filamentary structures. [Rajpurohit et al. 2018]

Citation

K. Rajpurohit et al 2018 ApJ 852 65. doi:10.3847/1538-4357/aa9f13

carbonaceous dust grain

This remarkable photograph (which spans only ~10 µm across; click for a full view) reveals what happens when you form dust grains in a laboratory under conditions similar to those of interstellar space. The cosmic life cycle of dust grains is not well understood — we know that in the interstellar medium (ISM), dust is destroyed at a higher rate than it is produced by stellar sources. Since the amount of dust in the ISM stays constant, however, there must be additional sources of dust production besides stars. A team of scientists led by Daniele Fulvio (Pontifical Catholic University of Rio de Janeiro and the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena) have now studied formation mechanisms of dust grains in the lab by mimicking low-temperature ISM conditions and exploring how, under these conditions, carbonaceous materials condense from gas phase to form dust grains. To read more about their results and see additional images, check out the paper below.

Citation

Daniele Fulvio et al 2017 ApJS 233 14. doi:10.3847/1538-4365/aa9224

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