Supernova remnants in the spiral galaxy NGC 6946. Field is the same as that shown in the full image above. [Long et al. 2019]
“A New, Larger Sample of Supernova Remnants in NGC 6946,” Knox S. Long et al 2019 ApJ 875 85. doi:10.3847/1538-4357/ab0d94
These beautiful images reveal the Cosmic Horseshoe, a gravitational lens system, in a 20-square-arcsecond field in five different Hubble filter bands. The lovely arc — a nearly complete Einstein ring — is created by the strong gravitational lensing of a background source (or sources) by a foreground object. In this case, the foreground object is a luminous red galaxy, visible as the bright source in the center of the ring. But what is the background, lensed source? Complex modeling of the lens system is necessary to disentangle the observations and reconstruct the source. A study led by Jun Cheng (Purdue University) uses a new method to fit different lens models to Hubble images of the Cosmic Horseshoe. While past models have focused on a scenario in which a single star-forming galaxy is lensed to form the Einstein ring, Cheng and collaborators show that there may be at least two background sources contributing to the total Einstein-ring flux of the Cosmic Horseshoe. For more information, check out the article below!
“Adaptive Grid Lens Modeling of the Cosmic Horseshoe Using Hubble Space Telescope Imaging,” Jun Cheng et al 2019 ApJ 872 185. doi:10.3847/1538-4357/ab0029
This unique way of looking at the sky (click for the full view) shows an octahedron-based projection of the 408 MHz all-sky map. Map projections are how we represent a spherical surface like the sky on flat surfaces like sheets of paper and computer monitors. Different projections are designed to meet different goals — and because astronomers use many different projections, large data sets should ideally be stored in a way that can easily be converted to the projection of choice. The Tessellated Octahedral Adaptive Spherical Transformation (TOAST) Projection, demonstrated above, is used by projects like the WorldWide Telescope to store data. In a recent study, a team of scientists led by Thomas McGlynn (NASA Goddard SFC) proposes that octahedron-based projections like this one make for an ideal intermediate representation; from this, it’s easy to convert the data to whatever projection is requested by the user. For a closer look at the fascinating math acrobatics behind projections — and for more awesome images of what those projections look like — check out the article below.
“Octahedron-based Projections as Intermediate Representations for Computer Imaging: TOAST, TEA, and More,” Thomas McGlynn et al 2019 ApJS 240 22. doi:10.3847/1538-4365/aaf79e
The image above (click for the full view) is a false-color, three-wavelength infrared look at an enormous ionized cloud in which new, large stars are just beginning to form. When young, massive stars are first born within a cloud of gas and dust, they eventually become hot enough to ionize a bubble of gas around them. When stars form near each other, as in a massive cluster, the individual bubbles can combine, producing large ionized regions known as giant H II regions. In a new survey, scientists are using the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) to map out all of the Milky Way giant H II regions in the mid-infrared, in order to better understand the earliest stages of massive and clustered star formation. W51A, shown above in two FORCAST wavelengths (20 µm shown in blue, 37 µm in green) and one Herschel (70 µm, shown in red), is one of the largest and brightest giant H II regions in our galaxy, and one of the first regions observed as part of the survey. A recent publication by SOFIA scientists Wanggi Lim and James De Buizer details what we’ve learned so far; check out the article below for more information, and keep an eye on AAS Nova for more on SOFIA science soon!
“Surveying the Giant H ii Regions of the Milky Way with SOFIA. I. W51A,” Wanggi Lim and James M. De Buizer 2019 ApJ 873 51. doi:10.3847/1538-4357/ab0288
These beautiful images (click for the full view) from a simulation of a Milky-Way-sized, isolated disk galaxy capture how the presence of gas affects a galaxy’s formation and evolution over time. The simulations, run by a team of scientists led by Woo-Young Seo (Seoul National University and Chungbuk National University, Republic of Korea), demonstrate that the amount of gas present in a forming galaxy influences the formation of features like spiral structure, a central bar, and even a nuclear ring — a site of intense star formation that encircles the very center of the galaxy. The images above (sized at 20 x 20 kpc) and below (same simulation, but zoomed to the central 2 x 2 kpc region) follow a warm galaxy model with a 5% gas fraction over the span of 5 billion years. For more information about the authors’ discoveries — and more gorgeous images of simulated, evolving galaxies — check out the article linked below.
“Effects of Gas on Formation and Evolution of Stellar Bars and Nuclear Rings in Disk Galaxies,” Woo-Young Seo et al 2019 ApJ 872 5. doi:10.3847/1538-4357/aafc5f
What’s with all the dots? You’re looking at the positions of thousands of stars observed by the Gaia mission in and around two nearby galaxies: Andromeda (M31) and Triangulum (M33). In a new study led by Roeland van der Marel (Space Telescope Science Institute and Johns Hopkins University), a team of scientists used stellar proper-motion observations from Gaia’s second data release, DR2, to track the 3D movement of these two galaxies. The precision of the Gaia data allowed the authors to update our best estimates about how these galaxies are interacting with each other and with the Milky Way, both now and in the future. Van der Marel and collaborators find that the Triangulum galaxy is likely on its very first infall into Andromeda, suggesting it’s not to blame for Andromeda’s previously formed tidal warps and tails. And Andromeda itself appears to be on a less direct path toward us than we’d previously thought, suggesting the collision between Andromeda and the Milky Way may be only glancing, and it won’t occur for another 4.5 billion years. For more on the authors’ conclusions, check out the article below.
“First Gaia Dynamics of the Andromeda System: DR2 Proper Motions, Orbits, and Rotation of M31 and M33,” Roeland P. van der Marel et al 2019 ApJ 872 24. doi:10.3847/1538-4357/ab001b
What do we know about the detailed structures of protoplanetary disks, the disks of gas in dust in which planets are born? A lot more now, thanks to the Disk Substructures at High Angular Resolution Project (DSHARP) — one of the first large programs conducted using the Atacama Large Millimeter/submillimeter Array (ALMA). DSHARP used the remarkable high resolution of ALMA to explore the substructures formed by solid particles within a sample of 20 nearby protoplanetary disks, revealing a myriad of different small-scale features that may help us to understand how planets first form and evolve in these dusty environments. The image above includes just a subset of the spectacular observations made with DSHARP at 1.3 mm; observations of the full set of 20 disks are shown below. These results come with an expansive public data release; be sure to check out the full Focus Issue on DSHARP to see more spectacular images and read about the authors’ discoveries!
Gallery of 240 GHz (1.25 mm) continuum emission images for the disks in the DSHARP sample. [Andrews et al. 2018]
“The Disk Substructures at High Angular Resolution Project (DSHARP). I. Motivation, Sample, Calibration, and Overview,” Sean M. Andrews et al. 2018 ApJL 869 L41. doi:10.3847/2041-8213/aaf741
The distant Coma Cluster contains over a thousand identified galaxies. The rapid motions of such galaxies in large clusters can drive a process known as ram-pressure stripping, in which gas is torn away from the galaxies as the galaxies speed through the intercluster medium. In the spectacular composite image shown above — created by combining false-color Hubble imaging with Hα data from the ground-based Subaru Suprime-Cam — a remarkable 200,000-light-year-long and extremely narrow (only 5,000 light-years wide) ram-pressure-stripped tail of gas can be seen to stream out from the center of the spiral galaxy D100 in the Coma Cluster. In a new study led by William Cramer (Yale University), a team of scientists has now used deep Hubble imaging to explore this tail in greater detail, particularly studying young stars that have formed in the tail. For more information and beautiful images, check out the paper below!
“Spectacular Hubble Space Telescope Observations of the Coma Galaxy D100 and Star Formation in Its Ram Pressure–stripped Tail,” W. J. Cramer et al 2019 ApJ 870 63. doi:10.3847/1538-4357/aaefff
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.
“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!
Artist’s impression of the Dragonfly mission concept, a relocatable rotorcraft that could land on Saturn’s moon Titan. [NASA]
“Titan’s Twilight and Sunset Solar Illumination,” Jason W. Barnes et al 2018 AJ 156 247. doi:10.3847/1538-3881/aae519