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composite X-ray, optical, and radio image of the galaxy NGC 253

The Silver Coin Galaxy, also known as NGC 253, is one of the nearest examples of a starburst galaxy — one that forms new stars faster than typical galaxies. In visible light, the nearly edge-on Silver Coin looks like a bright, narrow ellipse mottled with dark dust clouds. X-ray data tell a different story, though, as the image above shows. While the optical emission (H-alpha; green) is confined to the galaxy’s tilted disk, the X-ray emission (blue) extends perpendicular to the disk, tracing immense outflows powered by the galaxy’s fervent star formation. Millimeter emission (red) rounds out the three-color image. Using images and spectra from the Chandra X-ray Observatory, Sebastian Lopez (The Ohio State University) and collaborators investigated the physical properties of the galaxy’s outflows, finding that the galactic winds expel roughly 6 solar masses of gas each year. Spectral analysis revealed that the innermost region of the outflows are chemically enriched, providing a potential source for the metals found in the sparse gas between the Milky Way and its galactic neighbors. For more details about this windy starburst galaxy, be sure to check out the full article linked below!

Citation

“X-Ray Properties of NGC 253’s Starburst-Driven Outflow,” Sebastian Lopez et al 2023 ApJ 942 108. doi:10.3847/1538-4357/aca65e

composite optical and X-ray image of the Guitar Nebula

Roughly 2,700 light-years from Earth, a pulsar streaks across space at a blistering 765 kilometers per second. Its rapid motion through the interstellar medium creates a variety of structures, including the aptly named Guitar Nebula — an ever-expanding bow shock that billows in the pulsar’s wake, resembling the narrow head, long neck, and wide body of a guitar — and a filament that shines in X-ray light. In a recent publication, Martijn de Vries (Stanford University) and collaborators presented new Hubble Space Telescope and Chandra X-ray Observatory images of the pulsar and its surroundings, gaining a fresh perspective on a region that has been observed for more than 25 years. The new optical and X-ray data, combined with observations from the Panoramic Survey Telescope and Rapid Response System into the composite image shown above, allowed the team to analyze the subtle evolution of the Guitar Nebula. Among other changes, the team observed a ridge of bright emission moving through the X-ray filament, which they attributed to an injection of electrons and positrons decades ago. To learn more about the latest investigation of the Guitar Nebula — and to see the full version of the image above — be sure to check out the article below!

Citation

“A Quarter Century of Guitar Nebula/Filament Evolution,” Martijn de Vries et al 2022 ApJ 939 70. doi:10.3847/1538-4357/ac9794

Voyager 2 image of craters on Miranda

Voyager 2 images of Miranda's craters

Top row: Images of Miranda’s surface taken by Voyager 2. Bottom row: Those same images with muted and non-muted craters indicated. Click for high-resolution version. [Beddingfield & Cartwright 2022]

Do you see any differences between the craters in this photograph of Uranus’s moon Miranda? The images above and to the right, captured by the Voyager 2 spacecraft as it passed by the Uranian system in 1986, show that many of Miranda’s craters are “muted,” meaning that their edges are softer or more subtle than fresh craters. In a new research article, Chloe Beddingfield (SETI Institute and NASA Ames Research Center) and Richard Cartwright (SETI Institute) studied Miranda’s craters to investigate the cause of the moon’s muted terrain. Typically, craters evolve through erosion, relaxation, and the addition of material to the surface, and each process has a unique signature; erosion results in craters with steep, crumbling sides, relaxation causes sharp rims and raised floors, and the addition of material yields softened surface features like those seen on Miranda. Beddingfield and Cartwright estimated the thickness of the surface material, or regolith, and found that Miranda has among the thickest measured regolith of any body in the solar system. While Miranda’s regolith could have several origins, the authors suggest that particles raining down from Uranus’s rings are the most likely source. Hopefully, an upcoming Uranus orbiter will give fresh insight into Miranda’s geologic history and photograph never-before-seen sections of its surface.

Citation

“Miranda’s Thick Regolith Indicates a Major Mantling Event from an Unknown Source,” Chloe B. Beddingfield and Richard J. Cartwright 2022 Planet. Sci. J. 3 253. doi:10.3847/PSJ/ac9a4e

simulation results showing the charge density of plasma surrounding a pulsar

simulation results showing the charge density and current density of plasma surrounding a pulsar

Top row, left to right: simulated electron, positron, and ion charge densities. Bottom row, left to right: simulated electron, positron, and ion contributions to the overall electric current. Click for high-resolution version. [Hu and Beloborodov 2022]

When a massive star expires, its core can collapse into a rapidly spinning, city-sized sphere of neutrons with a powerful magnetic field — a pulsar. Pulsars get their name from the beams of radio waves they emit, which we observe as pulses of emission as the beam sweeps across our field of view. In a new publication, Rui Hu (Columbia University) and Andrei Beloborodov (Columbia University and Max Planck Institute for Astrophysics, Germany) used simulations to explore the charged particle environment near a pulsar, where fierce electric fields siphon electrons and their positively charged twins, positrons, from the pulsar’s blazing surface. The image above shows the simulated charge densities for electrons (left side) and positrons (right side). The full version of the image, shown to the right, includes the results for ions as well as the contribution of each species of charged particle to the overall electric current. These simulations by Hu and Beloborodov investigate where and how particles are accelerated, which is key to understanding how pulsars produce their radio emission and interpreting observed radio pulses. To learn more about modeling a pulsar’s particle environment, be sure to check out the full article below!

Citation

“Axisymmetric Pulsar Magnetosphere Revisited,” Rui Hu and Andrei M. Beloborodov 2022 ApJ 939 42. doi:10.3847/1538-4357/ac961d

images of NGC 3324 taken by the Spitzer Space Telescope and two of JWST's instruments

It’s been more than three months since astronomers waited with bated breath, endured an hour of the undeniable earworm that is the NASA hold music, and feasted their collective eyes upon the first image from JWST. While the public’s JWST experience began there, the road to the first JWST images began years earlier for the scientists and administrators working behind the scenes. Let’s take a quick look at the creation of those first images — an immense effort that culminated in 26,000 news articles viewed 120 billion times.

In 2017, representatives from NASA, the Canadian Space Agency, the European Space Agency, and the Space Telescope Science Institute began the process of selecting JWST’s first targets. How do you select five targets from an entire universe of possibilities? You ask a bunch of astronomers, of course! The selection committee polled members of the American Astronomical Society to get a broad list of targets, which the JWST Early Release Observations committee narrowed down to just 70 that reflected JWST’s four main science themes — stars and galaxies in the early universe, galaxy formation, stellar evolution, and planetary systems near and far. The five-member Early Release Observations Core Implementation Team, led by Klaus Pontoppidan (Space Telescope Science Institute), made the final target decisions.

After the data for the first images were collected in June and July 2022, the image visualization team faced a daunting task: combining data taken at many different wavelengths into images that are both informative and beautiful. With few exceptions, the team opted to follow chromatic ordering, assigning redder colors to longer wavelengths and bluer colors to shorter wavelengths, while selecting filters that highlight the physical characteristics of the target. For example, in the images of the Carina Nebula shown above, the filters were selected to trace ionized gas, jets and outflows, dust, and polycyclic aromatic hydrocarbons — organic molecules containing carbon atoms arranged in rings.

Though the iconic images from JWST have long since captured our imaginations (and taken over our desktop backgrounds), the image processing work continues. Check out the full article linked below for more details on how the first JWST images were created — and be sure to take a look at the full gallery of JWST images released so far!

Citation

“The JWST Early Release Observations,” Klaus M. Pontoppidan et al 2022 ApJL 936 L14. doi:10.3847/2041-8213/ac8a4e

model results showing conditions around AU Microscopii 90 minutes after the passage of a coronal mass ejection

model results for 90 minutes after the passage of a coronal mass ejection

Model results showing the conditions 90 minutes after a coronal mass ejection for a field of view 175 times the stellar radius (left) and 60 times the stellar radius (right). The yellow lobes show the surface on which the plasma density is ten times higher than the typical density. Planetary orbits are shown in blue, and the sphere surrounding the central star shows the magnetic field strength at half the distance to the inner planet. The magenta and green lines show the magnetic fields that loop back to the star’s surface or extend outward, respectively. Click for high-resolution version. [Fraschetti et al. 2022]

How do high-energy particles affect the atmospheres of exoplanets? For the two Neptune-sized planets closely orbiting AU Microscopii, it’s an important question. At just 22 million years old, AU Microscopii is highly active, producing high-energy particles that can, in extreme cases, cause a planet’s atmosphere to evaporate over time. In a recent publication, a team led by Federico Fraschetti (Center for Astrophysics ∣ Harvard & Smithsonian and Lunar and Planetary Laboratory) modeled the passage of high-energy particles as they travel outward from AU Microscopii. To understand how stellar coronal mass ejections — enormous explosions of plasma and magnetic fields from a star’s atmosphere — affect the passage of high-energy particles, the team compared their results for a quiescent environment to the turbulent aftermath of a coronal mass ejection. The images above and to the right show the model results for the coronal mass ejection case. Fraschetti and collaborators found that the disruption caused by a coronal mass ejection causes huge fluctuations in the number of high-energy particles that strike the planets, with the maximum particle flux reaching values 2–3 orders of magnitude higher than experienced by Earth. To learn more about how energetic particles navigate the complex plasma environment around a young star, be sure to read the full article below!

Citation

“Stellar Energetic Particle Transport in the Turbulent and CME-disrupted Stellar Wind of AU Microscopii,” Federico Fraschetti et al 2022 ApJ 937 126. doi:10.3847/1538-4357/ac86d7

two photographs of the experimental setup used in this study

Today’s the day! At 7:14 pm EDT, the Double Asteroid Redirection Test (DART) spacecraft will slam into the asteroid Dimorphos to explore the possibility that we can reroute an asteroid headed toward Earth by smashing a spacecraft into it. Back on Earth, a research team led by James Walker (Southwest Research Institute) prepared for today’s impact with a collision of their own; the team loaded limestone and hematite stones into a wooden frame, pictured above, secured the stones with concrete, and launched a 3-centimeter-wide aluminum sphere at the target — at 5.44 kilometers per second. The impact completely dismantled the target, which was designed to approximate the properties of a rubble-pile asteroid, and reduced much of the rock and concrete to a fine powder. While the particulars of the setup are different from those of DART and Dimorphos, this test gives us a way to assess the modeling tools that researchers will use to understand the outcome of the DART mission. To learn more about this experiment and check out the aftermath, be sure to read the full article below.

Bonus

Want to learn more about the DART mission? You can read about other preparations for and expected insights from the DART–Dimorphos impact in a recent Focus Issue of the Planetary Science Journal.

Citation

“Momentum Enhancement from a 3 cm Diameter Aluminum Sphere Striking a Small Boulder Assembly at 5.4 km s−1,” James D. Walker et al 2022 Planet. Sci. J. 3 215. doi:10.3847/PSJ/ac854f

models of Prokofiev crater on Mercury

models of various properties of Prokofiev crater on Mercury

New models of various properties of Prokofiev crater on Mercury: (a) elevation, (b) illumination, (c) maximum temperature, and (d) depth at which ice is stable. These maps have a resolution of 125 meters per pixel. Click for high-resolution version. [Barker et al. 2022]

With daytime temperatures soaring to 427℃ (800℉), Mercury seems like an unlikely place to find ice, but the poles of the airless planet can be surprisingly frosty. Using images and elevation data from the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft, a team led by Michael Barker (NASA’s Goddard Space Flight Center) inspected a permanently shadowed north polar crater named Prokofiev, which contains a radar-bright region thought to be surface ice. As shown in the images to the right, Barker and collaborators modeled the crater’s elevation, illumination, maximum temperature, and depth below the surface at which water ice could be stable. This modeling confirmed that the crater has the right conditions to host surface ice, and further analysis suggests that the radar-bright region may be a layer of ice up to 26 meters thick. The ice isn’t pure water, though — part of the ice is covered by a dark silicate or hydrocarbon material, the exact nature of which is unknown. To learn more about this icy investigation, be sure to check out the full article below!

Citation

“New Constraints on the Volatile Deposit in Mercury’s North Polar Crater, Prokofiev,” Michael K. Barker et al 2022 Planet. Sci. J. 3 188. doi:10.3847/PSJ/ac7d5a

a newly characterized substellar companion to a Sun-like star in the Hyades cluster

four observations of the newly discovered object

Images of the companion object (circled) taken over the course of a year. The companion object is detected with a signal-to-noise ratio ranging from 10 to 19. Click to enlarge. [Kuzuhara et al. 2022]

Astronomers have photographed a substellar object in orbit around a star in the Hyades, the nearest star cluster to Earth, for the first time. Previous data from the Gaia and Hipparcos satellites showed the Sun-like star HIP 21152 accelerating under the influence of an unseen companion. Now, a team led by Masayuki Kuzuhara (Astrobiology Center of the National Institutes of Natural Sciences and the National Astronomical Observatory of Japan) has obtained new Subaru and Keck telescope images, shown above and to the right, of HIP 21152 and its surroundings. These images reveal HIP 21152’s companion, which Kuzuhara and collaborators determined to be a 27.8-Jupiter-mass object orbiting the star at a distance of 17.5 au. Spectra of the object suggest that it is a T dwarf with a temperature between 1200K and 1300K. This discovery is exciting for a number of reasons, chief among them the object’s membership in the Hyades cluster; because the age of the cluster is well known, the newly discovered object will provide a useful reference point for studies of how substellar objects evolve over time.

Citation

“Direct-imaging Discovery and Dynamical Mass of a Substellar Companion Orbiting an Accelerating Hyades Sun-like Star with SCExAO/CHARIS,” Masayuki Kuzuhara et al 2022 ApJL 934 L18. doi:10.3847/2041-8213/ac772f

diagram of a magnetic flux rope

In June 2012, the Sun released a powerful solar flare and an explosive burst of plasma and magnetic fields called a coronal mass ejection. Days later, this solar storm swept through the inner solar system, where multiple spacecraft sampled the passing plasma and magnetic fields. In a recent publication, a team led by Qiang Hu (University of Alabama in Huntsville) used a new quasi-three-dimensional fitting method to analyze spacecraft data of the event and deduce the structure of the passing bundle of magnetic field lines. The image above shows the simulated strength and direction — with yellow being strong and outward pointing and blue being strong and inward pointing — of the magnetic field lines that the Wind spacecraft crossed as the storm traveled past it. (In this image, the spacecraft would be located roughly halfway along the length of the field lines.) These simulations show three-dimensional winding behavior, highlighted by the red lines in the image above, that was not present in one- or two-dimensional models of the same event. To learn more about this event and the authors’ new modeling technique, be sure to check out the full article below!

Citation

“Validation and Interpretation of a Three-dimensional Configuration of a Magnetic Cloud Flux Rope,” Qiang Hu et al 2022 ApJ 934 50. doi:10.3847/1538-4357/ac7803

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