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comet 67P's coma

This series of images (click for the full view!) features the nucleus of comet 67P/Churymov-Gerasimenko. The images were taken with the Wide Angle Camera of Rosetta’s OSIRIS instrument as Rosetta orbited comet 67P. Each column represents a different narrow-band filter that allows us to examine the emission of a specific fragment species, and the images progress in time from January 2015 (top) to June 2015 (bottom). In a recent study, Dennis Bodewits (University of Maryland) and collaborators used these images to analyze the comet’s inner coma, the cloud of gas and dust produced around the nucleus as ices sublime. OSIRIS’s images allowed the team to explore how the 67P’s inner coma changed over time as the comet approached the Sun — marking the first time we’ve been able to study such an environment at this level of detail. To read more about what Bodewits and collaborators learned, you can check out their paper below!

Citation

D. Bodewits et al 2016 AJ 152 130. doi:10.3847/0004-6256/152/5/130

core-collapse SN simulation

This stunning snapshot (click for a closer look!) is from a simulation of a core-collapse supernova. Despite having been studied for many decades, the mechanism driving the explosions of core-collapse supernovae is still an area of active research. Extremely complex simulations such as this one represent best efforts to include as many realistic physical processes as is currently computationally feasible. In this study led by Luke Roberts (a NASA Einstein Postdoctoral Fellow at Caltech at the time), a core-collapse supernova is modeled long-term in fully 3D simulations that include the effects of general relativity, radiation hydrodynamics, and even neutrino physics. The authors use these simulations to examine the evolution of a supernova after its core bounce. To read more about the team’s findings (and see more awesome images from their simulations), check out the paper below!

Citation

Luke F. Roberts et al 2016 ApJ 831 98. doi:10.3847/0004-637X/831/1/98

NGC 5907

This negative image of NGC 5907 (originally published in Martinez-Delgado et al. 2008; click for the full view!) reveals the faint stellar stream that encircles the galaxy, forming loops around it — a fossil of a recent merger. Mergers between galaxies come in several different flavors: major mergers, in which the merging galaxies are within a 1:5 ratio in stellar mass; satellite cannibalism, in which a large galaxy destroys a small satellite less than a 50th of its size; and the in-between case of minor mergers, in which the merging galaxies have stellar mass ratios between 1:5 and 1:50. These minor mergers are thought to be relatively common, and they can have a significant effect on the dynamics and structure of the primary galaxy. A team of scientists led by Seppo Laine (Spitzer Science Center – Caltech) has recently analyzed the metallicity and age of the stellar population in the stream around NGC 5907. By fitting these observations with a stellar population synthesis model, they conclude that this stream is an example of a massive minor merger, with a stellar mass ratio of at least 1:8. For more information, check out the paper below!

Citation

Seppo Laine et al 2016 AJ 152 72. doi:10.3847/0004-6256/152/3/72

Venus transits

This stunning image was captured by the Solar Dynamics Observatory’s Atmospheric Imaging Assembly in June 2012 during the transit of Venus across the face of the Sun. A recent study led by Masoud Afshari (University of Palermo, Italy and INAF-OAPA) presents an analysis of high-energy imaging of Venus’s silhouette as it crossed the Sun. This imaging reveals X-ray and ultraviolet emission coming from the dark side of Venus during the transit — which Afshari and collaborators conclude is not due to instrumental scattering, but instead has an origin directly related to the planet. The authors suggest that this light could be emitted from the Sun and then scattered by Venus’s very long magnetotail, and they wonder if such an effect might be important for exoplanets as well! For more information, check out the paper below.

Citation

M. Afshari et al 2016 AJ 152 107. doi:10.3847/0004-6256/152/4/107

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

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