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DISCO tests

Creating the codes that are used to numerically model astrophysical systems takes a lot of work — and a lot of testing! A new, publicly available moving-mesh magnetohydrodynamics (MHD) code, DISCO, is designed to model 2D and 3D orbital fluid motion, such as that of astrophysical disks. In a recent article, DISCO creator Paul Duffell (University of California, Berkeley) presents the code and the outcomes from a series of standard tests of DISCO’s stability, accuracy, and scalability.

From left to right and top to bottom, the test outputs shown above are: a cylindrical Kelvin-Helmholtz flow (showing off DISCO’s numerical grid in 2D), a passive scalar in a smooth vortex (can DISCO maintain contact discontinuities?), a global look at the cylindrical Kelvin-Helmholtz flow, a Jupiter-mass planet opening a gap in a viscous disk, an MHD flywheel (a test of DISCO’s stability), an MHD explosion revealing shock structures, an MHD rotor (a more challenging version of the explosion), a Flock 3D MRI test (can DISCO study linear growth of the magnetorotational instability in disks?), and a nonlinear 3D MRI test.

Check out the gif below for a closer look at each of these images, or follow the link to the original article to see even more!

test outputs

Citation

Paul C. Duffell 2016 ApJS 226 2. doi:10.3847/0067-0049/226/1/2

debris disk around solar analog

HD 207917

The Hubble image of a second circumstellar debris disk, HD 207917, and its best-fit model.

This is a new deep observation made by Hubble’s Space Telescope Imaging Spectrograph of the tilted debris disk surrounding the star HD 207129. In a recent study led by Glenn Schneider (Seward Observatory, University of Arizona), three known, nearby circumstellar disks were imaged by Hubble in order to gain a better understanding of the disks’ ring-like structure. The three central stars of these disks are all G-type solar analogs, and the debris rings bear many similarities to our own Kuiper belt. Imaging of debris disks like these can help us to learn more about how solar systems form around stars like our own. For more information, check out the paper below!

Citation

Glenn Schneider et al 2016 AJ 152 64. doi:10.3847/0004-6256/152/3/64

WISE Milky Way

X-shaped bulge

The X-shaped bulge is even more evident in this image, wherein a simple exponential disk model has been subtracted off. [Adapted from Ness & Lang 2016]

This contrast-enhanced image of the Milky Way, observed by the Wide-Field Infrared Survey Explorer (WISE), clearly reveals that the bulge of stars at the center of our galaxy is shaped like a large “X”. The boxy nature of the Milky Way’s bulge was revealed by satellite image in 1995, but in recent years, star counts along the line of sight toward the bulge have suggested that the bulge may be X-shaped. It was unclear whether this apparent morphology was due to the difference in the distributions of different stellar populations, or if the actual physical structure of the bulge was X-shaped. But these new WISE images, produced by astronomers Melissa Ness (Max Planck Institute for Astronomy) and Dustin Lang (University of Toronto and University of Waterloo), now provide firm evidence that the Milky Way’s bulge actually is X-shaped, supplying clues as to how our galaxy’s center may have formed. This morphology is not uncommon; observations of other barred galaxies reveal similar X-shaped profiles. To learn more, check out the paper below!

Citation

Melissa Ness and Dustin Lang 2016 AJ 152 14. doi:10.3847/0004-6256/152/1/14

Binary simulation

GG Tau

An image of GG Tau, a quadruple system, from the Gemini North telescope in Hawaii. The two white stars each mark a binary system; the bottom star marks the binary GG Tau A. [Daniel Potter/University of Hawaii Adaptive Optics Group/Gemini Observatory/AURA/NSF]

Last week, we discussed a model for how binary star systems might form. The image above (click for the full view!) captures a scene from another study of the formation of multiple-star systems: a series of 2D hydrodynamics simulations of a self-gravitating binary system surrounded by a circumbinary disk. These simulations were performed by Andrew Nelson (Los Alamos National Laboratory) and Francesco Marzari (University of Padua, Italy), who were attempting to better understand observations of GG Tau A, one of two binaries in the quadruple star system GG Tau. Nelson and Marzari use their simulations to demonstrate how spiral structures could form within the circumbinary disk, and how material from the circumbinary disk can substantially feed the individual accretion disks around each star, if the stars are in a wide orbit. To find out more about what they learned (and to see more awesome simulation images!), check out the paper below.

Citation

Andrew F. Nelson and F. Marzari 2016 ApJ 827 93. doi:10.3847/0004-637X/827/2/93

Eri II

This beautiful 13’ x 13’ image (click for the full view!) holds more than meets the eye. Look closely at the small concentration of blue stars just to the left of center. This is Eridanus II, one of nine new ultra-faint galaxies discovered just last year around the Milky Way. Detected as part of the Dark Energy Survey (DES) and presented in a study led by Sergey E. Koposov (Institute of Astronomy, Cambridge), these new galaxies add to a growing list of very dim satellites that orbit within the Milky Way’s potential. Since their discovery, these DES satellites have been used to answer a number of astronomical questions. In particular, the large dark-matter fraction of these ultra-faint galaxies makes them excellent laboratories for testing models of dark matter in the universe. Check back with us on Wednesday to learn more about what Eridanus II has revealed about dark matter! And for more information on the nine DES-discovered ultra-faint satellites, check out the paper below.

Citation

Sergey E. Koposov et al 2015 ApJ 805 130. doi:10.1088/0004-637X/805/2/130

LMC supernova remnants

These vibrant images (click for the full view!) of supernova remnants in the Large Magellanic Cloud (LMC) were created by mapping data from the Chandra X-ray Telescope into three colors: red for 300–720 eV, green for 720–1100 eV, and blue for 1100–7000 eV. Three scientists at University of Texas at Arlington — Andrew Schenck, Sangwook Park, and Seth Post — created these maps in order to probe the composition of the LMC’s interstellar medium. The forward shocks of supernova remnants sweep up the interstellar medium as they expand, heating it and causing it to emit the X-rays that Chandra observes. Schenck, Park and Post used Chandra’s observations of these remnants to make new measurements of the interstellar metallicities in the LMC. To find out more, check out the paper below!

Citation

Andrew Schenck et al 2016 AJ 151 161. doi:10.3847/0004-6256/151/6/161

Jupiter global map

Zonal wind profile for Jupiter, describing the speed and direction of its winds at each latitude. [Simon et al. 2015]

Zonal wind profile for Jupiter, describing the speed and direction of its winds at each latitude. [Simon et al. 2015]

This global map of Jupiter’s surface (click for the full view!) was generated by the Hubble Outer Planet Atmospheres Legacy (OPAL) program, which aims to create new yearly global maps for each of the outer planets. Presented in a study led by Amy Simon (NASA Goddard Space Flight Center), the map above is the first generated for Jupiter in the first year of the OPAL campaign. It provides a detailed look at Jupiter’s atmospheric structure — including the Great Red Spot — and allowed the authors to measure the speed and direction of the wind across Jupiter’s latitudes, constructing an updated zonal wind profile for Jupiter.

In contrast to this study, the Juno mission (which will be captured into Jupiter’s orbit today after a 5-year journey to Jupiter!) will be focusing more on the features below Jupiter’s surface, studying its deep atmosphere and winds. Some of Juno’s primary goals are to learn about Jupiter’s composition, gravitational field, magnetic field, and polar magnetosphere. You can follow along with the NASATV livestream as Juno arrives at Jupiter tonight; orbit insertion coverage starts at 10:30 EDT.

Citation

Amy A. Simon et al 2015 ApJ 812 55. doi:10.1088/0004-637X/812/1/55

This beautiful mosaic of images of the Whirlpool galaxy (M51) and its companion was taken with the Advanced Camera for Surveys on the Hubble Space Telescope. This nearby, “grand-design spiral” galaxy has a rich population of star clusters, making it both a stunning target for imagery and an excellent resource for learning about stellar formation and evolution. In a recent study, Rupali Chandar (University of Toledo) and collaborators cataloged over 3,800 compact star clusters within this galaxy. They then used this catalog to determine the distributions for the clusters’ ages, masses, and sizes, which can provide important clues as to how star clusters form, evolve, and are eventually disrupted. You can read more about their study and what they discovered in the paper below.

Citation

Rupali Chandar et al 2016 ApJ 824 71. doi:10.3847/0004-637X/824/2/71

EN130114

This image of a fireball was captured in the Czech Republic by cameras at a digital autonomous observatory in the village of Kunžak. This observatory is part of a network of stations known as the European Fireball Network, and this particular meteoroid detection, labeled EN130114, is notable because it has the lowest initial velocity of any natural object ever observed by the network. Led by David Clark (University of Western Ontario), the authors of a recent study speculate that before this meteoroid impacted Earth, it may have been a Temporarily Captured Orbiter (TCO). TCOs are near-Earth objects that make a few orbits of Earth before returning to heliocentric orbits. Only one has ever been observed to date, and though they are thought to make up 0.1% of all meteoroids, EN130114 is the first event ever detected that exhibits conclusive behavior of a TCO. For more information on EN130114 and why TCOs are important to study, check out the paper below!

Citation

David L. Clark et al 2016 AJ 151 135. doi:10.3847/0004-6256/151/6/135

This remarkable false-color, mid-infrared image (click for the full view!) was produced by the Wide-field Infrared Survey Explorer (WISE). It captures a tantalizing view of Sh 2-207 and Sh 2-208, the latter of which is one of the lowest-metallicity star-forming regions in the Galaxy. In a recent study led by Chikako Yasui (University of Tokyo and the Koyama Astronomical Observatory), a team of scientists has examined this region to better understand how star formation in low-metallicity environments differs from that in the solar neighborhood. The authors’ analysis suggests that sequential star formation is taking place in these low-metallicity regions, triggered by an expanding bubble (the large dashed oval indicated in the image) with a ~30 pc radius. You can find out more about their study by checking out the paper below!

Citation

Chikako Yasui et al 2016 AJ 151 115. doi:10.3847/0004-6256/151/5/115

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