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dwarf galaxy merger simulation

How do globular clusters — massive and dense gravitationally bound stellar systems — form? A team of scientists led by Natalia Lahén (University of Helsinki, Finland) explores the possibility that the mergers of gas-rich dwarf galaxies can result in the formation of massive, low-metallicity clusters of stars much like the local globular clusters we observe today. The beautiful series of images above are frames from the authors’ hydrodynamical simulations of the aftermath of a dwarf-galaxy merger. The three sets of panels show surface density of stars (left) and gas (center), and the thermal gas pressure (right), at two times during the simulation (the bottom panels are from 2 million years later than the top). The simulations demonstrate the formation of hundreds of stellar clusters in the filamentary gas structures after merger, including some with properties like local globular clusters. For more information, you can check out the article below.

Citation

“The Formation of Low-metallicity Globular Clusters in Dwarf Galaxy Mergers,” Natalia Lahén et al 2019 ApJL 879 L18. doi:10.3847/2041-8213/ab2a13

SMBH merger

What happens to accreting gas when two supermassive black holes merge? The dramatic scene above shows the behavior of disk gas in a still from a simulation of such a merger; the two smaller black disks represent the black holes, and the larger disk in the center is a cutout at the center of mass. In this new study, a team of scientists led by Dennis Bowen (Los Alamos National Laboratory and Rochester Institute of Technology) have conducted the first exploration of how magnetized mini-disks around supermassive black holes can couple to the accreting gas surrounding the binary in the moments shortly before the black holes merge. The team’s simulations show that asymmetries in this coupling can drive strong oscillations in the system — and these could introduce distinctive, increasingly rapid fluctuations in the electromagnetic emission that we might be able to detect from supermassive black hole mergers that are surrounded by gas. To learn more about the authors’ discoveries, check out the article below.

Citation

“Quasi-periodicity of Supermassive Binary Black Hole Accretion Approaching Merger,” Dennis B. Bowen et al 2019 ApJ 879 76. doi:10.3847/1538-4357/ab2453

PDS 70 system

The panels above show 10” x 14” images of dust emission from the disk that surrounds the young star PDS 70, captured with the Atacama Large Millimeter/submillimeter Array (ALMA). See that purple blob of emission on the inside-right of the disk in the center panel? According to a new study led by Andrea Isella (Rice University), that’s dust emission from what is likely a circumplanetary disk — a disk of gas and dust surrounding the newly forming giant planet PDS 70c, feeding its growth and possibly providing the material that will later form into one or more moons around the planet.

The PDS 70 system made headlines last year when its first planet, PDS 70b, was directly imaged (you can see it best in the background VLT/SPHERE image in the right panel).

In the grand scheme of a giant planet’s lifetime, the period of time when it is still surrounded by a circumplanetary disk is short, so PDS 70 system is one of the few instances where we’ve managed to capture this moment. By studying PDS 70, we hope to learn more about how gas giants — like our own Jupiter or Saturn — and their moon systems form. To learn more, check out the article below.

Citation

“Detection of Continuum Submillimeter Emission Associated with Candidate Protoplanets,” Andrea Isella et al 2019 ApJL 879 L25. doi:10.3847/2041-8213/ab2a12

T 37 cluster

This 53’-wide, false-color infrared image reveals the field containing the star cluster Trumpler 37, located ~3,000 light-years away. Here, T 37 can be seen near the head of IC 1396A, the colorful, bright-rimmed globule near the center of the image. In a recent study led by Huan Meng (Steward Observatory, University of Arizona), a team of scientists has used observations from the United Kingdom Infrared Telescope (UKIRT) spanning two full years to study the variability of stars in this young stellar cluster. The length of their study allowed them to identify 119 members of the cluster — discovering even low-mass members down to brown-dwarf size. By studying the stars in this cluster, Meng and collaborators hope to better understand what different factors drive young stellar objects like these to vary in emission — could it be changing accretion rates? Magnetic activity? Flares? Starspots? The effects of circumstellar disks? To find out what the authors learned, you can check out the article below.

Citation

“Near-infrared Variability of Low-mass Stars in IC 1396A and Tr 37,” Huan Y. A. Meng et al 2019 ApJ 878 7. doi:10.3847/1538-4357/ab1b14

Ho II X-1

This complex composite image reveals Holmberg II X-1, an example of an ultraluminous X-ray source (ULX). As the name suggests, ULXs are objects that shine anomalously bright in X-rays; they’re not as bright as active galactic nuclei, but they’re brighter than any known isotropic stellar process. What powers these unusual sources? Led by Ryan Lau (Japan Aerospace Exploration Agency and California Institute of Technology), a team of scientists is searching for more details by studying ULXs in a different wavelength: infrared. The false-color image above shows what the ULX Ho II X-1 looks like in combined Spitzer/IRAC 4.5 μm (red), HST/WFC Hα (green), HST/WFC V-band (blue) wavelengths. The source and its nebula — roughly 60 light-years across — are contained within the white box. Lau and collaborators’ search for infrared counterparts to nearly 100 ULXs show that some ULXs are redder in infrared than others, which the authors propose is a consequence of thermal emission from circumstellar or circumbinary dust. To learn more about we’ve discovered about these odd sources, check out the article below.

Citation

“Uncovering Red and Dusty Ultraluminous X-Ray Sources with Spitzer,” Ryan M. Lau et al 2019 ApJ 878 71. doi:10.3847/1538-4357/ab1b1c

pre-planetary nebulae

This collection of ten spectacular Hubble images (click for a closer look) reveals what are known as pre-planetary nebulae: glowing clouds of gas formed shortly after a star reaches the end of the asymptotic giant branch (AGB) evolutionary phase. During a star’s AGB phase, gas flows off of the star in the form of slow winds, filling the environment around it. After the end of the star’s AGB lifetime, it can emit jets that punch through the winds — shaping the surrounding gas into the hollow, candle-flame-shaped lobes seen in these images. In a recent study led by Bruce Balick (University of Washington, Seattle), a team of scientists has used models to explore the formation histories of these candle-like pre-planetary nebulae. To learn more about the team’s work, check out the article below.

Citation

“Models of the Mass-ejection Histories of Pre-planetary Nebulae. III. The Shaping of Lobes by Post-AGB Winds,” Bruce Balick et al 2019 ApJ 877 30. doi:10.3847/1538-4357/ab16f5

SNR CTB 1

In the dramatic false-color radio images above, captured by the Canadian Galactic Plane Survey (background) and the Very Large Array (zoomed-in inset), a pulsar — a rapidly spinning, magnetized neutron star — is seen plunging out of a supernova remnant and taking off into interstellar space. The green cross marks the center of the supernova remnant CTB 1, and the green circle marks the location of the pulsar PSR J0002+6216. The tail of radio-emitting gas extending behind the pulsar toward the nebula is a dead giveaway to this object’s origin: the pulsar was likely born from the very same supernova explosion that produced the remnant. Supernova explosions don’t have perfect symmetry, and the pulsar likely received a natal kick that sent it tearing away from its birthplace at tremendous speeds, causing it to eventually overtake the expanding shell of gas and dust. In a recent study led by Frank Schinzel (National Radio Astronomy Observatory), a team of scientists presents and discusses the evidence that this runaway pulsar came from CTB 1. To read more, check out the article below.

Citation

“The Tail of PSR J0002+6216 and the Supernova Remnant CTB 1,” F. K. Schinzel et al 2019 ApJL 876 L17. doi:10.3847/2041-8213/ab18f7

solar cavity eruption

The dramatic image above reveals the expansion of a large coronal cavity as it erupts from the Sun’s surface in the form of a coronal mass ejection. This is a combination of LASCO (background) and SWAP (overlay) observations; click to see the larger field, which spans 3 x 5 solar radii (the white quarter-circle marks one solar radius). To better understand what triggers powerful solar ejections, a team of scientists led by Ranadeep Sarkar (Udaipur Solar Observatory, India) has pieced together observations over time of a coronal cavity that was witnessed in 2010. This low-density cavity formed above the Sun’s surface and hung peacefully in the lower corona for nearly two weeks before erupting violently in a surge of plasma and radiation.

coronal cavity

This image of the cavity was taken with SDO nearly two weeks before the LASCO/SWAP image above. Here, the cavity is much smaller and sits in the lower corona above a prominence. [Adapted from Sarkar et al. 2019]

Sarkar and collaborators used observations from multiple vantage points — from the SDO, STEREO, SWAP, and LASCO observatories — to track the cavity’s evolution from a quiet bubble in the lower corona (see image to the right) to eruption into space. To see more images of the cavity and find out more about what the authors learned, check out the article below.

Citation

“Evolution of the Coronal Cavity From the Quiescent to Eruptive Phase Associated with Coronal Mass Ejection,” Ranadeep Sarkar et al 2019 ApJ 875 101. doi:10.3847/1538-4357/ab11c5

NGC 6946

NGC 6946 SNRs

Supernova remnants in the spiral galaxy NGC 6946. Field is the same as that shown in the full image above. [Long et al. 2019]

The face-on spiral galaxy NGC 6946 is revealed in the stunning false-color image above (click for the full view), constructed from observations of three emission lines with the WIYN telescope at Kitt Peak Observatory. NGC 6946 is undergoing a major starburst, earning it the moniker “the Fireworks Galaxy”; evidence of its star-forming activity can be seen in the 10 supernovae (labeled in yellow) that have been observed within it since 1917. In a recent study led by Knox Long (Space Telescope Science Institute and Eureka Scientific, Inc.), scientists have undertaken a new optical search of NGC 6946 for supernova remnants — the ghostly remains of past stellar explosions. The resulting data to the right shows that NGC 6946 is positively rich with supernova remnants; green circles indicate remnant candidates found in a previous study, and blue circles indicate new remnant candidates discovered in optical in the current study. Red markers indicate objects for which the authors obtained spectra, reported in this study. To learn more, check out the article below.

Citation

“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

Cosmic Horseshoe

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!

Citation

“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

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