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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

FluxCompensator

One of the challenges of astronomy is connecting theoretical models of distant objects to observations. Numerical simulations can produce ideal visualizations of objects and their physical processes, but this doesn’t necessarily represent what we’ll be able to see when we look at these sources with instruments that have finite resolution and sensitivity. Two scientists with the Max Planck Institute for Astronomy in Germany, Christine Koepferl and Thomas Robitaille, have now created a tool to help us make these connections: an open-source Python package called the FluxCompensator. This software package allows scientists to post-process the output of their numerical simulations, adding observational effects to the data like telescope point-spread functions, transmission curves, finite pixel resolution, noise, and reddening. The outputs of the FluxCompensator are images more consistent with what we would expect to be able to observe with our available telescopes and instruments.

In the figure above (click for a closer look), the authors display three simulated sources: a) a young stellar object, b) a star-forming region, and c) the center of a galaxy. The top panels show synthetic single-band observations extracted directly from the models, whereas the bottom panels are synthetic three-color images produced by the FluxCompensator that mimic the observational effects expected if these sources were observed as part of the GLIMPSE survey with Spitzer (a and b) or the Hi-GAL survey with Herschel (c). To read more about FluxCompensator, check out the article below.

Citation

Christine M. Koepferl and Thomas P. Robitaille 2017 ApJ 849 3. doi:10.3847/1538-4357/aa8666

nuclear star clusters

This collection of images (click for the full view) from the Hubble Space Telescope reveals the nuclear star clusters of early-type galaxies located in the Virgo cluster. These dense clusters of stars are only ~10 light-years in size, and they have been found to lie at the core of galaxies throughout the universe. A recent study led by Chelsea Spengler (University of Victoria, Canada) presents an analysis of 39 of these nuclei and their hosts in the Virgo cluster, exploring the masses, metallicities and ages of the nuclei. The authors used their observations to better understand how nuclei form: are they the result of smaller star clusters falling to the center of their host galaxies and merging? Or were they formed in situ from gas funneled into the galactic centers? To learn more about what the authors discovered, check out the paper below.

Citation

Chelsea Spengler et al 2017 ApJ 849 55. doi:10.3847/1538-4357/aa8a78

VVV galactic center

In this map of the innermost galaxy, which spans only a few square degrees at the Milky Way’s center, we can see the locations of more than 31 million objects obtained from the VISTA Variables in the Vía Láctea (VVV) survey. This near-infrared atlas traces stellar populations in the inner Milky Way that are dimmed and reddened by interstellar dust and gas — a process known as extinction — in a predictable way. Led by Javier Alonso-García (University of Antofagasta and the Millennium Institute of Astrophysics in Chile), a team of scientists has now used the VVV measurements of these stars to better understand the distribution of gas and dust that causes extinction in our inner galaxy — particularly in the most central, highly reddened, and crowded areas of the Milky Way. For more information, check out the paper below.

Citation

Javier Alonso-García et al 2017 ApJL 849 L13. doi:10.3847/2041-8213/aa92c3

chemical mixing

How do stars mix chemicals in their interiors, leading to the abundances we measure at their surfaces? Two scientists from the Planetary Science Institute in Arizona, Tamara Rogers (Newcastle University, UK) and Jim McElwaine (Durham University, UK), have investigated the role that internal gravity waves have in chemical mixing in stellar interiors. Internal gravity waves — not to be confused with the currently topical gravitational waves — are waves that oscillate within a fluid that has a density gradient. Rogers and McElwaine used simulations to explore how these waves can cause particles in a star’s interior to move around, gradually mixing the different chemical elements. Snapshots from four different times in their simulation can be seen below, with the white dots marking tracer particles and the colors indicating vorticity. You can see how the particles move in response to wave motion after the first panel. For more information, check out the paper below!

time snapshots of mixing

Citation

T. M. Rogers and J. N. McElwaine 2017 ApJL 848 L1. doi:10.3847/2041-8213/aa8d13

formation of rapidly rotating black hole

These stills from a simulation show the evolution (from left to right and top to bottom) of a high-mass X-ray binary over 1.1 days, starting after the star on the right fails to explode as a supernova and then collapses into a black hole. Many high-mass X-ray binaries — like the well-known Cygnus X-1, the first source widely accepted to be a black hole — host rapidly spinning black holes. Despite our observations of these systems, however, we’re still not sure how these objects end up with such high rotation speeds. Using simulations like that shown above, a team of scientists led by Aldo Batta (UC Santa Cruz) has demonstrated how a failed supernova explosion can result in such a rapidly spinning black hole. The authors’ work shows that in a binary where one star attempts to explode as a supernova and fails — it doesn’t succeed in unbinding the star — the large amount of fallback material can interact with the companion star and then accrete onto the black hole, spinning it up in the process. You can read more about the authors’ simulations and conclusions in the paper below.

Citation

Aldo Batta et al 2017 ApJL 846 L15. doi:10.3847/2041-8213/aa8506

The inset in this Solar Dynamics Observatory image shows a close-up view of a stunning coronal fan extending above the Sun’s atmosphere. These sweeping loops were observed on 7 March 2012 by a number of observatories, revealing the first known evidence of standing slow magnetoacoustic waves in cool coronal fan loops. The oscillations of the loops, studied in a recent article led by Vaibhav Pant (Indian Institute of Astrophysics), were triggered by blast waves that were generated by X-class flares from the distant active region AR 11429 (marked with the yellow box at left). The overplotted X-ray curve in the top right corner of the image (click for the full view) shows the evolution of the flares that perturbed the footpoints of the loops. You can check out the video of the action below, and follow the link to the original article to read more about what these oscillations tell us about the Sun’s activity.

 

Citation

V. Pant et al 2017 ApJL 847 L5. doi:10.3847/2041-8213/aa880f

cosmic velocity web

You may have heard of the cosmic web, a network of filaments, clusters and voids that describes the three-dimensional distribution of matter in our universe. But have you ever considered the idea of a cosmic velocity web? In a new study led by Daniel Pomarède (IRFU CEA-Saclay, France), a team of scientists has built a detailed 3D view of the flows in our universe, showing in particular motions along filaments and in collapsing knots. In the image above (click for the full view), surfaces of knots (red) are embedded within surfaces of filaments (grey). The rainbow lines show the flow motion, revealing acceleration (redder tones) toward knots and retardation (bluer tones) beyond them. You can learn more about Pomarède and collaborators’ work and see their unusual and intriguing visualizations in the video they produced, below. Check out the original paper for more information.

Citation

Daniel Pomarède et al 2017 ApJ 845 55. doi:10.3847/1538-4357/aa7f78

M33

These spectacular images are of M33, otherwise known as the Triangulum Galaxy — a spiral galaxy roughly 3 million light-years away. The views on the left and in the center are different Wide-field Infrared Survey Explorer (WISE) filters, and the view on the right is a full-resolution look at the H I gas distribution in M33’s inner disk, made with data from the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope and Arecibo. In a new study, a team of authors led by Zacharie Sie Kam (University of Ouagadougou, Burkina Faso; University of Montreal, Canada) uses the H I gas observations to explore how the mass is distributed throughout M33 and how the gas moves as the galaxy’s disk rotates. To read more about what they learned, check out the paper below.

Citation

S. Z. Kam et al 2017 AJ 154 41. doi:10.3847/1538-3881/aa79f3

ring galaxies

Hoag's Object

Hoag’s Object, an example of a ring galaxy. [NASA/Hubble Heritage Team/Ray A. Lucas (STScI/AURA)]

The above image (click for the full view) shows PanSTARRS observations of some of the 185 galaxies identified in a recent study as “ring galaxies” — bizarre and rare irregular galaxies that exhibit stars and gas in a ring around a central nucleus. Ring galaxies could be formed in a number of ways; one theory is that some might form in a galaxy collision when a smaller galaxy punches through the center of a larger one, triggering star formation around the center. In a recent study, Ian Timmis and Lior Shamir of Lawrence Technological University in Michigan explore ways that we may be able to identify ring galaxies in the overwhelming number of images expected from large upcoming surveys. They develop a computer analysis method that automatically finds ring galaxy candidates based on their visual appearance, and they test their approach on the 3 million galaxy images from the first PanSTARRS data release. To see more of the remarkable galaxies the authors found and to learn more about their identification method, check out the paper below.

Citation

Ian Timmis and Lior Shamir 2017 ApJS 231 2. doi:10.3847/1538-4365/aa78a3

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