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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.


“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.


“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.


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

What would the Milky Way look like if the supermassive black hole at its center was a little more active? This stunning HST/WFC3 image of NGC 6744, spanning 160” x 160” (click for the whole view), may provide us with a reasonable guess! NGC 6744 is a nearby galaxy that’s morphologically very similar to our own — with the exception of the presence of an apparent low-luminosity active galactic nucleus at its center. The image to the right is a 10” x 10” zoom-in on the core of this galaxy, which was recently studied with the Gemini South Multi-Object Spectrograph by a team of scientists led by Patrícia da Silva (University of São Paulo, Brazil). The authors’ observations suggest that this galaxy’s nucleus was more luminous in the past — perhaps as a result of a merger — and has now settled down. For more information, check out the article below.


Patrícia da Silva et al 2018 ApJ 861 83. doi:10.3847/1538-4357/aac6e3

supernova Refsdal

The insets in this beautiful Hubble image of the MACS 1149 cluster shows the well-known supernova Refsdal, which appears as multiple copies of the same supernova due to strong gravitational lensing by a foreground galaxy. A new study led by Claudio Grillo (University of Milan, Italy and University of Copenhagen, Denmark) has now used the time delay between the multiple images of supernova Refsdal as a means of measuring the Hubble constant, a fundamental cosmological parameter that defines scales like the universe’s size, expansion rate, and geometry. By calculating the Hubble constant using time delays in a lens galaxy cluster, Grillo and collaborators confirm the possibility of an approach independent from techniques previously used to measure the constant. To learn more about their study, check out the article below.


C. Grillo et al 2018 ApJ 860 94. doi:10.3847/1538-4357/aac2c9

Are you planning to watch 4th of July fireworks tonight? Here’s a little preview on a cosmic scale! The images above — roughly 8’ across and captured by the Canada–France–Hawaii Telescope (CFHT) on the left and the Isaac Newton Telescope on the right — show the stunning planetary nebula NGC 6543 in all its large-scale glory. This may look a little different from images you’re used to seeing of NGC 6543, however: the most commonly seen view is of just the inner ~45” of this nebula (shown in the top image third from the left in the grid below). In a new study led by Xuan Fang (The University of Hong Kong and the National Astronomical Observatories, NAOC, in China), a team of scientists has used the CFHT to explore the extended molecular hydrogen structures of 11 planetary nebulae. The team’s work help us to better understand how these nebulae spread out into their surroundings after being expelled from dying, low-mass stars, and how the gas of the nebulae interacts with the interstellar medium. For more information — and lots of spectacular images of planetary nebulae — check out the article linked below!

planetary nebulae

The inner regions of just a few of the planetary nebulae the authors explore in this study. [Adapted from Fang et al. 2018]


Xuan Fang et al 2018 ApJ 859 92. doi:10.3847/1538-4357/aac01e

Phoebe water-ice

These maps of Saturn’s moon Phoebe show different views of the water-ice absorption across a model of Phoebe’s surface, revealing the body’s icy-rock nature. At 213 km across, Phoebe is the largest of Saturn’s highly inclined irregular satellites, thought to have been captured long ago from the outer solar system. In a recent publication, scientists Wesley Fraser (Queen’s University Belfast, UK) and Michael Brown (California Institute of Technology) have reanalyzed high-resolution spectral imaging of this moon from Cassini’s flyby to explore the water-ice distribution across Phoebe’s surface. Fraser and Brown use their observations to argue that Phoebe’s surface was once quite water poor; its current water-rich state is a consequence of a violent history of impacts, which dredged up water-rich subsurface material. Impact histories like Phoebe’s may explain why there’s so much variation in the amount of water-ice seen on outer-solar-system bodies: more collisions may mean more water-ice. To learn more about the study (and to see more awesome maps and images of Phoebe’s surface!), check out the article below.


Wesley C. Fraser and Michael E. Brown 2018 AJ 156 23. doi:10.3847/1538-3881/aac213

Spitzer view of N55

What do molecular clouds look like outside of our own galaxy? See for yourself in the images above and below of N55, a molecular cloud located in the Large Magellanic Cloud (LMC). In a recent study led by Naslim Neelamkodan (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan), a team of scientists explore N55 to determine how its cloud properties differ from clouds within the Milky Way. The image above reveals the distribution of infrared-emitting gas and dust observed in three bands by the Spitzer Space Telescope. Overplotted in cyan are observations from the Atacama Submillimeter Telescope Experiment tracing the clumpy, warm molecular gas. Below, new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the sub-parsec-scale molecular clumps in greater detail, showing the correlation of massive clumps with Spitzer-identified young stellar objects (crosses). The study presented here indicates that this cloud in the LMC is the site of massive star formation, with properties similar to equivalent clouds in the Milky Way. To learn more about the authors’ findings, check out the article linked below.

ALMA view of N55


Naslim N. et al 2018 ApJ 853 175. doi:10.3847/1538-4357/aaa5b0

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.


Zhaohuan Zhu and James M. Stone 2018 ApJ 857 34. doi:10.3847/1538-4357/aaafc9


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.


Martín A. Guerrero et al 2018 ApJ 857 80. doi:10.3847/1538-4357/aab669

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