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image of the solar corona in a region of quiet sun.

How does the Sun’s outermost atmosphere — the solar corona — become heated to a million degrees Kelvin? The answer may lie in what’s pictured here: the quiet Sun. This extreme ultraviolet image, taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) in 2019, shows a region of the Sun spanning roughly 300 x 350 arcseconds (click for the full view). The image captures the quiet Sun — the ordinary, background roiling of the corona, unblemished by large magnetic features like active regions or coronal holes. In a new study, scientists Vishal Upendran and Durgesh Tripathi (Inter University Centre for Astronomy and Astrophysics, India) combine SDO AIA images of the quiet Sun with new models to better understand how heat may be injected into the solar corona on a continuous basis — even when the Sun is quiet. They show that impulsive events — tiny, constantly occurring nanoflares — can pump enough energy into the quiet-Sun corona to explain its mysteriously large temperature. For more information, check out the original article below.


“On the Impulsive Heating of Quiet Solar Corona,” Vishal Upendran and Durgesh Tripathi 2021 ApJ 916 59. doi:10.3847/1538-4357/abf65a

A gold-wrapped spacecraft sits on the right side of the image, in a room completely covered in blue conical protrusions.

On the right side of this photograph is the integrated payload and spacecraft of Chandrayaan-2, an Indian Space Research Organisation (ISRO) lunar exploration mission. In the image, the mission’s Dual-Frequency synthetic aperture radar (DFSAR) instrument is being tested prior to launch in an anechoic chamber — a room designed to minimize reflections and echos at specific wavelengths, allowing scientists to evaluate the function of an instrument. Chandrayaan-2 launched in 2019 and is currently orbiting the Moon, mapping out the lunar surface and exploring its thin atmosphere. In a new publication, a team of scientists led by Sriram Bhiravarasu (Space Applications Centre, ISRO) provides a preliminary report on DFSAR’s performance and describes what we may be able to learn from the radar polarization measurements made by this instrument — for instance, how the rockiness of craters evolve with time on the Moon’s surface. To learn more (and to see some cool radar images of the Moon’s surface), check out the original article below.


“Chandrayaan-2 Dual-frequency Synthetic Aperture Radar (DFSAR): Performance Characterization and Initial Results,” Sriram S. Bhiravarasu et al 2021 Planet. Sci. J. 2 134. doi:10.3847/PSJ/abfdbf

a cross section of a disk shows streamlines with swirls and swoops illustrating the motion of dust

full DSHARP gallery

Examples from DSHARP of some of the structure observed in protoplanetary disks. Click to enlarge. [Andrews et al. 2018]

In the simulated cross-section of a protoplanetary disk shown above (see the full figure below), dust swirls around as a consequence of the recent passage of an orbiting planet. This simulation was led by Jiaqing Bi (毕嘉擎; University of Victoria, Canada) to explore what happens to the disk of gas and dust surrounding a young star when a baby planet orbits within it.

Protoplanetary disks often exhibit a dramatic structure of gaps and rings. But in some systems, the edges of gaps are puffy and ill-defined, suggesting agitated dust; in others, the gaps are sharp and well-defined, suggesting the dust there is well-settled. Could the presence of an orbiting planet explain both kinds of structure?

Bi and collaborators use their 3D simulations to model how a planet stirs up the gas and dust at the edges of gaps, and show how the properties of both the planet and the dust affect how quickly the dust settles after the planet’s passage — and thus, how sharp the disk gaps appear. To find out more about the authors’ results, check out the original article below.

Two plots show a disk in cross-section with overplotted streamlines showing gas and dust motion.

Streamlines showing the gas (top) and dust (bottom) motion in a disk, shown in cross-section, due to a planet orbiting at R/Rref=1. [Bi et al. 2021]


“Puffed-up Edges of Planet-opened Gaps in Protoplanetary Disks. I. Hydrodynamic Simulations,” Jiaqing Bi et al 2021 ApJ 912 107. doi:10.3847/1538-4357/abef6b

Two images showing swirls and eddies in the atmospheres of a hot jupiter; the left represents the planet's nightside, and the right represents the planet's dayside.

Hot Jupiters are giant exoplanets that orbit very close to their host stars, generally in a 1:1 spin–orbit ratio that ensures they always present the same face to their host. How does the atmosphere of a hot Jupiter respond to the bombardment of radiation on only one side of the planet? In a new study led by James Cho (CCA, Flatiron Institute), a team of scientists has conducted detailed simulations to find out. The delicate vorticity maps above (click for a closer look) show the nightside (left) and dayside (right) of a simulated hot Jupiter atmosphere. Cho and collaborators’ high-resolution simulations are designed to accurately capture small-scale eddies and waves that arise in the atmosphere as the unequal heating drives flows. The authors show that intense storms result across the hot Jupiter on both small and large scales, leading to global variability and chaotic mixture of the atmosphere. To learn more about the authors’ results, check out the original article below.


“Storms, Variability, and Multiple Equilibria on Hot Jupiters,” James Y-K. Cho et al 2021 ApJL 913 L32. doi:10.3847/2041-8213/abfd37

Photograph of the Sun during an eclipse reveals large-scale stalks extending through the sun's corona. Two are labeled "streamer" and one is labeled "pseudostreamer".

This stunning image of the Sun during a total solar eclipse, included in today’s article with permission from astrophotographer Nicolas Lefaudeux, illustrates an intriguing structure in the solar corona: a pseudostreamer. Streamers and pseudostreamers structure the Sun’s outer atmosphere — the corona — on enormous scales. True streamers, which are long-lived and relate to the global dipole magnetic field of the Sun, separate regions of opposite magnetic field in the corona. Pseudostreamers, on the other hand, are transient structures that separate regions of the same polarity. Can you tell which is which in the image above? Click on the image to see the labels. A team of scientists led by Roger Scott (US Naval Research Laboratory) has now created the first detailed 3D numerical simulations of the formation of a pseudostreamer and explored the implications for the origins of the extremely variable slow solar wind, a stream of magnetized particles that flows from the Sun. To learn more about the team’s results, check out the original article below.


“The Dynamic Formation of Pseudostreamers,” Roger B. Scott et al 2021 ApJ 913 64. doi:10.3847/1538-4357/abec4f

Six panels show different magnetic field line configurations where reconnection may occur.

Magnetic reconnection — when magnetic fields rearrange themselves, breaking neighboring field lines and rejoining them in a new configuration — is a critical process in astrophysical plasmas. This rearrangement converts energy stored in the magnetic fields into kinetic and thermal energy, playing a major role in phenomena like solar flares or the Earth’s aurora. But reconnection is not yet well understood — especially when operating in three dimensions! In particular, it’s notoriously difficult to identify the sites where reconnection occurs in 3D. In a recent study, scientist Giovanni Lapenta (Space Science Institute; KU Leuven University, Belgium) presents a new indicator that can be used to detect reconnection sites in both observations and simulations of 3D plasmas. The images above, adapted from figures in the study, show the magnetic field configurations for six different probable reconnection sites identified via Lapenta’s process in a 3D simulation of a turbulent outflow. To learn more, check out the original article below.


“Detecting Reconnection Sites Using the Lorentz Transformations for Electromagnetic Fields,” Giovanni Lapenta 2021 ApJ 911 147. doi:10.3847/1538-4357/abeb74

Compilation of 12 images of the sun taken during a solar eclipse, so the extended solar corona and streams of solar wind are visible.

The figure above (click for the full view) contains 6 pairs of images of the Sun captured during different total solar eclipses between 2008 and 2020. During an eclipse, the Moon blocks the bright light of the solar disk and reveals the complex structure of the Sun’s corona. Each beautifully detailed pair of images above shows a white-light picture (left), and an overlay of white light with Fe XI 789.2 nm (red) and Fe XIV 530.3 nm (green) emission (right). A team of scientists led by Shadia Habbal (Institute for Astronomy, University of Hawaii) has used these images and complementary in situ observations from NASA’s Advanced Composition Explorer — a spacecraft that measures the properties of solar wind particles — to explore the source regions of different solar wind streams. By studying where solar wind streams arise, the authors are able to better understand the physical processes that shape these flows of energetic particles from our host star. To learn more about their work (and to see more spectacular images!), check out the article below.


“Identifying the Coronal Source Regions of Solar Wind Streams from Total Solar Eclipse Observations and in situ Measurements Extending over a Solar Cycle,” Shadia R. Habbal et al 2021 ApJL 911 L4. doi:10.3847/2041-8213/abe775

Photograph of radio emission from a jet composited with a cluster of bright galaxies.

This stunning composite image (click for the full view!) reveals the radio emission (shown in red) from a bent jet that was launched from the galaxy NGC 1272, the bright source just to the right of the image center. The 12’ x 12’ image of the Perseus galaxy cluster is captured by the Sloan Digital Sky Survey; the brightest central galaxy of the cluster, NGC 1275, can be seen to NGC 1272’s left. A new publication led by Marie-Lou Gendron-Marsolais (European Southern Observatory) presents high-resolution Very Large Array images of the detailed radio structures in the Perseus cluster. The authors use these new data to study how the galaxy’s movement as it falls into the cluster, as well as the bulk motions of the intracluster gas, shape the powerful radio jet into the dramatic shapes we see here. For more information, check out the original article below.


“VLA Resolves Unexpected Radio Structures in the Perseus Cluster of Galaxies,” M.-L. Gendron-Marsolais et al 2021 ApJ 911 56. doi:10.3847/1538-4357/abddbb

mosaic of small images of newly discovered gravitational lens systems

You’re looking at just a handful (click here to see a few more!) of the 1,210 strong gravitational lens candidates newly discovered in a recent study that analyzed data from the Dark Energy Spectroscopic Instrument (DESI) Legacy Surveys. Strong gravitational lensing occurs when light from a background source bends around a massive foreground object (like a galaxy). This bending smears the light from the background source into arcs, rings, and multiple images. In a study led by Xiaosheng Huang (University of San Francisco), scientists have now used trained neural networks to search the DESI data for new strong gravitational lensing systems, finding a treasure trove of candidates. The new discoveries dramatically extend our set of known strong lens systems — in 2018, when the first iteration of this project began, there were only a few hundred confirmed strong lenses. To read more about the project and its results, check out the original article below.


“Discovering New Strong Gravitational Lenses in the DESI Legacy Imaging Surveys,” X. Huang et al 2021 ApJ 909 27. doi:10.3847/1538-4357/abd62b

Diagram illustrating formation of icy exomoons in the radiation belt surrounding a giant planet.

This schematic shows one possible solution to an intriguing white-dwarf mystery, in which two white dwarfs have been observed to contain an overabundance of the rare element beryllium. Unlike many heavy elements, beryllium isn’t formed in stars; instead, it’s produced by spallation, in which larger atomic nuclei break up after being bombarded by high-energy protons. So how did this unexpected element end up in the atmospheres of white dwarfs? A new publication led by Alexandra Doyle (UC Los Angeles) proposes a path: white dwarfs may become polluted by beryllium after accreting the icy exomoons of giant planets orbiting the dwarf. If these exomoons formed within the radiation belts of their planets, their composition could include spallogenic nuclides like beryllium. When the moons accrete onto the white dwarf, that beryllium then pollutes the white dwarf’s atmosphere. Doyle and collaborators illustrate the extreme environment in which these beryllium-enriched ices form in the image above. To learn more, check out the original article below.


“Icy Exomoons Evidenced by Spallogenic Nuclides in Polluted White Dwarfs,” Alexandra E. Doyle et al 2021 ApJL 907 L35. doi:10.3847/2041-8213/abd9ba

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