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N49

N49 is a supernova remnant located about 160,000 light-years away in the Large Magellanic Cloud. As the dramatic three-color Chandra X-ray image of N49 shows above, the interactions between the supernova shock wave and the surrounding interstellar medium have led to the formation of complex structure. In a new publication led by Yumiko Yamane and Hidetoshi Sano (Nagoya University), a team of scientists details a study using radio-continuum observations from a host of telescopes (Mopra, ASTE, ALMA, and ATCA) to complement prior X-ray observations of N49. The 1.42-GHz observations are shown in contours overlaid on the Chandra image above. The study reveals clumps of carbon monoxide on the outer edge of the N49 bubble, providing evidence for dynamical interactions between the gas and the supernova remnant shock wave. To read more about what the authors found, check out the paper below.

Citation

“ALMA Observations of Supernova Remnant N49 in the LMC. I. Discovery of CO Clumps Associated with X-Ray and Radio Continuum Shells,” Y. Yamane et al 2018 ApJ 863 55. doi:10.3847/1538-4357/aacfff

To celebrate today’s successful touchdown of NASA’s Insight lander on Mars (yay!), today we’re featuring this haunting image of a Martian sunset, captured by the Mars Exploration Rover Spirit on May 19, 2005. This image is included in a new publication led by Jason Barnes (University of Idaho) that explores the conditions that may exist at twilight and sunset for a future mission — this time landing not on Mars, but on Saturn’s moon Titan.

The New Frontiers Phase-A mission concept Dragonfly is a proposed relocatable rotorcraft lander that could be sent to Titan’s surface to study prebiotic chemistry, assess water-based and hydrocarbon-based habitability, and search for potential chemical biosignatures. In their study, Barnes and collaborators use models to determine the type of lighting conditions such a lander could expect around sunset on Titan, which would influence what type of experiments the lander could do.

To learn more about this study, check out the original article below. And cheers to the successful exploration — past, present, and future — of the universe around us!

Dragonfly

Artist’s impression of the Dragonfly mission concept, a relocatable rotorcraft that could land on Saturn’s moon Titan. [NASA]

Citation

“Titan’s Twilight and Sunset Solar Illumination,” Jason W. Barnes et al 2018 AJ 156 247. doi:10.3847/1538-3881/aae519

solar current sheet

This spectacular composition of the Solar Dynamics Observatory’s AIA 193 Å, white-light K, and LASCO C2 images (click for the full view) captures a long, thin current sheet extending to the right of the Sun. Solar current sheets are structures with large length-to-width ratios that arise in the plasma of the solar corona; in these sheets, electric current is enhanced and magnetic field is dissipated. Led by Xin Cheng (Nanjing University, China), a team of scientists has examined the super-hot current sheet formed during an X8.2-class solar flare on 10 September, 2017. The team’s analysis suggests that magnetic reconnection in solar eruptions doesn’t happen uniformly in space and time. Instead, the current sheet may contain fragmented structures, and reconnection dissipates magnetic energy turbulently, heating the plasma and driving jets. To learn more about the outcomes of this study, check out the article below.

Citation

“Observations of Turbulent Magnetic Reconnection within a Solar Current Sheet,” X. Cheng et al 2018 ApJ 866 64. doi:10.3847/1538-4357/aadd16

MWA 1.28 MHz observations

Look closely. What do you see in the dead center of this 4° x 4° stacked radio image? If your answer is “not much”, you’re absolutely right — and that’s super interesting! The observations above were made by the Murchison Widefield Array (MWA) as it shadowed the pointings of the Australian Square Kilometre Array Pathfinder (ASKAP). During the time the two instruments synchronized their pointings, ASKAP detected several fast radio bursts — extremely energetic and brief flashes of radio emission — including one that should have appeared in the center of the MWA image above. But MWA spotted nothing but weak candidate sources (circled in green) that were later discarded.

Why did MWA turn up nothing? A primary difference between the arrays is that ASKAP scans at a higher radio frequency than MWA — 700 MHz to 1.8 GHz, compared to MWA’s 80 to 300 MHz. This null result in MWA’s observations therefore has important implications for understanding mysterious fast radio bursts: it means that either the bursts don’t emit below a certain radio frequency (which raises the question: why not?), or that something is blocking the lower-frequency radio signal on its way to Earth (which raises the question: what?). To learn more about the team’s findings, check out the article below.

Citation

“No Low-frequency Emission from Extremely Bright Fast Radio Bursts,” M. Sokolowski et al 2018 ApJL 867 L12. doi:10.3847/2041-8213/aae58d

core collapse simulation

Modeling the collapse of a stellar core and the supernova explosion that follows — with the inclusion of all of the complex physics involved in these processes — is notoriously difficult. Even more difficult: doing this in three dimensions. In a new study, Evan O’Connor (Stockholm University, Sweden) and Sean Couch (Michigan State University) present the results of an extensive set of 3D core-collapse supernova simulations that include the physics of transporting neutrinos in multiple dimensions, high-resolution hydrodynamics, and approximate general relativistic gravity. These simulations show that capturing the 3D behavior is critical: the large-scale aspherical motion in the star’s silicon and oxygen shells aids the expansion of the shock and brings the star closer to exploding. The figure below (click for a closer look) shows the difference between two models that do (top row) and don’t (bottom row) include aspherical perturbations in these shells, as the star’s entropy evolves in time from left to right. For more information and images, check out the original study linked below.

core-collapse evolution simulation

Citation

“Exploring Fundamentally Three-dimensional Phenomena in High-fidelity Simulations of Core-collapse Supernovae,” Evan P. O’Connor and Sean M. Couch 2018 ApJ 865 81. doi:10.3847/1538-4357/aadcf7

CHIME

The Canadian Hydrogen Intensity Mapping Experiment, or CHIME, is a novel radio telescope originally intended to map features in hydrogen gas to measure dark energy. It has an additional mission now, however: CHIME will search the sky for signs of new fast radio bursts (FRBs). FRBs — energetic transient radio pulses that last only a few milliseconds — were first discovered about a decade ago, and though we’ve only observed ~30 of them so far, some estimates suggest they occur at a rate of several hundred to a few thousand per day across the sky! CHIME’s large field of view, high sensitivity, and wide bandwidth will help us hunt for these explosive events. In a new report by the CHIME/FRB collaboration, the team details this unique telescope, located in British Columbia. CHIME is made up of four 20-m x 100-m semicylindrical paraboloid reflectors, giving it its unusual appearance. The team expects that when CHIME begins science operations, it will detect FRBs at a rate of 2–42 FRBs per sky per day. For more information, check out the article below!

Citation

“The CHIME Fast Radio Burst Project: System Overview,” The CHIME/FRB Collaboration et al 2018 ApJ 863 48. doi:10.3847/1538-4357/aad188

circumnuclear disks and rings

These dramatic simulated images (click for the full view) reveal some of the circumnuclear gas structures that can form from the tidal disruption of molecular clouds in the nucleus of a galaxy. In a study led by Alessandro Trani (The University of Tokyo, Japan; International School for Advanced Studies, Italy; INAF-Astronomical Observatory of Padua, Italy), a team of scientists has conducted a series of simulations exploring what happens to gas in a galactic nucleus consisting of a supermassive black hole and a nuclear star cluster. Their work shows that the gas can be drawn into extended disks or compact rings, depending on whether the black hole’s influence is stronger than that of the nuclear star cluster. To read more about their outcomes, check out the paper below.

Citation

“Forming Circumnuclear Disks and Rings in Galactic Nuclei: A Competition Between Supermassive Black Hole and Nuclear Star Cluster,” Alessandro A. Trani et al 2018 ApJ 864 17. doi:10.3847/1538-4357/aad414

M100

These side-by-side images (click for a closer look) show the spiral galaxy Messier 100 in two views: the image on the right is taken with the Very Large Telescope in optical bands, and the image on the left is an infrared view captured by the Spitzer space telescope. In a new study led by Bruce Elmegreen (IBM Research Division, T.J. Watson Research Center), a team of scientists has further analyzed Spitzer’s observations of M100. The authors focus on the regularly spaced infrared-bright, star-forming clumps that lie along the dusty filaments — which, while clearly visible in infrared, often can’t be seen in the optical. The regularity of the spacing and size of these clumps suggest that star formation within the spiral arms of M100 occurs as a result of gravitational instabilities in gas that was accumulated by spiral density waves moving through the galaxy. For more information, check out the original article below.

Citation

“Regularly Spaced Infrared Peaks in the Dusty Spirals of Messier 100,” Bruce G. Elmegreen et al 2018 ApJ 863 59. doi:10.3847/1538-4357/aacf9a

SDSS J0924+0510

How can we hunt down so-called dual active galactic nuclei (AGN) — pairs of accreting supermassive black holes that are likely headed for a merger after the collision of their host galaxies? The above Hubble image (broader ~40” x 40” view on the left, 8” x 8” zoom-in on the right) reveals two separate stellar bulges lying at the center of the minor galaxy merger SDSS J0924+0510. In a new study led by Xin Liu (University of Illinois at Urbana-Champaign), a team of scientists further explore this merger with Hubble to demonstrate that the two stellar bulges contain two spatially distinct regions showing [O III] emission — a strong indication that there are two obscured AGN independently ionizing gas at the heart of this merger. The authors show that the dual AGN are separated by only ~3,000 light-years — just a hair’s-breadth in cosmic distances! For more information, check out the original article below.

Citation

“Hubble Space Telescope Wide Field Camera 3 Identifies an rp  = 1 Kpc Dual Active Galactic Nucleus in the Minor Galaxy Merger SDSS J0924+0510 at z = 0.1495,” Xin Liu et al 2018 ApJ 862 29. doi:10.3847/1538-4357/aac9cb

MWC 758

This image, captured with the Very Large Telescope SPHERE adaptive optics in Chile, reveals the large-scale spiral arms visible in the MWC 758 protoplanetary disk, located less than 500 light-years away. Such arms are thought to be triggered by one of two mechanisms: gravitational instability, or a companion orbiting within the disk. A team of scientists led by Bin Ren (The Johns Hopkins University) has recently used observations of these arms over a decade-long baseline to track the speed of rotation of the arms. Since companion-driven arms corotate with their drivers, this exercise which could reveal the location of a planetary-mass, unseen companion that drives the arms. Ren and collaborators find that the most likely location for such a planet to orbit in this disk is at 89 AU, just outside of the visible spiral arms. For more information, check out the article below.

Citation

Bin Ren et al 2018 ApJL 857 L9. doi:10.3847/2041-8213/aab7f5

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