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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

image of the andromeda galaxy with data plotted on top

Even though the Andromeda Galaxy is among our nearest galactic neighbors, there’s still much about it that we don’t know. Since the 1950s, astronomers have debated whether Andromeda, similar to the Milky Way, hosts a central bar of stars. Discerning Andromeda’s structure is key to understanding how it formed and evolved, but its tilted orientation makes it difficult to do so from our vantage point. Now, a team led by Zi-Xuan Feng (Shanghai Astronomical Observatory and University of the Chinese Academy of Sciences) has presented new evidence that shows Andromeda is indeed a barred galaxy. The above image shows the new results superimposed atop observations from the Hubble Space Telescope and the Subaru and Mayall ground-based telescopes. The red and blue symbols indicate the locations of velocity jumps — shocks — identified in emission from oxygen and hydrogen gas. Using simulations, Feng and collaborators show that shocks of this type cannot form without a rotating bar of stars. To learn more about the observations and simulations that led to this conclusion, be sure to check out the full article below!

Citation

“Large-scale Hydrodynamical Shocks as the Smoking-gun Evidence for a Bar in M31,” Zi-Xuan Feng et al 2022 ApJ 933 233. doi:10.3847/1538-4357/ac7964

images of eight nearly edge on galaxies

collage of 12 galaxy images

The 12 galaxies in the sample, ordered from high to low stellar mass. Click for high-resolution version. [Gilhuly et al. 2022]

Studying galaxy halos is key to understanding how galaxies form and evolve. These diffuse, extended regions contain clues to a galaxy’s past interactions, such as elongated streams of stars that mark the capture of globular clusters or satellite galaxies. However, because halos are faint and can spread a great distance beyond the luminous disk of a galaxy, observing them can be challenging. A team led by Colleen Gilhuly (University of Toronto, Canada) used the Dragonfly Telephoto Array to survey a dozen nearby edge-on galaxies, pictured above and to the right, and measure the starlight coming from each galaxy’s halo — and, by extension, estimate the mass of the halo stars. Gilhuly and collaborators found that the stellar halo mass fractions (the mass of stars in the halo compared to the mass of stars in the galaxy as a whole) varied widely among the galaxies in their sample, but the overall mass of stars in these galaxies was correlated with the masses of their stellar halos. To learn more about this survey of nearby galaxies, be sure to check out the full article below!

Citation

“Stellar Halos from the Dragonfly Edge-on Galaxies Survey,” Colleen Gilhuly et al 2022 ApJ 932 44. doi:10.3847/1538-4357/ac6750

representative-color optical image of the taffy galaxies

When galaxies clash, is star formation heightened or quenched? The Taffy galaxies (UGC 12914/5) provide an excellent setting to probe this question. These two galaxies, shown above in a representative-color optical image from the Sloan Digital Sky Survey, collided head on just 25–30 million years ago, resulting in a bridge of turbulent gas that stretches across the space between them. A team led by Philip Appleton (California Institute of Technology/Infrared Processing and Analysis Center) carried out new Atacama Large Millimeter/submillimeter Array (ALMA) observations, the locations of which are marked with red circles in the image above, to study this interacting pair of galaxies. The team’s observations of carbon monoxide gas suggest that the filaments and clumps within the bridge that connects the two galaxies are likely gravitationally unbound. Without a source of pressure to keep them together, these potentially star-forming features are likely to dissipate within 2–5 million years. Despite this, star formation presses on in isolated regions. To learn more about the results of this galactic interaction, be sure to check out the full article below!

Citation

“The CO Emission in the Taffy Galaxies (UGC 12914/15) at 60 pc Resolution. I. The Battle for Star Formation in the Turbulent Taffy Bridge,” P. N. Appleton et al 2022 ApJ 931 121. doi:10.3847/1538-4357/ac63b2

three images of simulated dust grains

What do you see when you look at these images? Clouds? Islands? Legos? Think smaller: simulated dust particles! Modelers often approximate dust grains as spheres, but real dust grains likely come in a range of shapes. A new publication led by Jessica Arnold (Army Research Laboratory) explores the impact of dust shapes on models of debris disks around young stars. Irregularly shaped dust grains, like those shown above, have been used to reproduce spectra of dust grains in a lab setting as well as those of dusty comets, making them a promising tool for modelers. Arnold and collaborators modeled dust grains three ways — as solid spheres, porous spheres, and randomly generated irregular shapes — to constrain the properties of the debris disk surrounding AU Microscopii. The three shapes yielded different best-fitting dust grain size distributions for AU Microscopii’s disk, suggesting that future modeling should account for the uncertainties introduced by grain shapes. To learn more about how astronomers decipher distant dust, be sure to read the full article below!

Citation

“Stumbling over Planetary Building Blocks: AU Microscopii as an Example of the Challenge of Retrieving Debris-disk Dust Properties,” Jessica A. Arnold et al 2022 ApJ 930 123. doi:10.3847/1538-4357/ac63a9

optical image of the bow shock around a black widow pulsar

Though it’s not uncommon for stars to snack on their stellar companions from time to time, it’s rare for them to eat their associates entirely. This is the scenario proposed for black widow pulsars — tiny, dense stellar remnants that rotate rapidly, produce beams of radio emission and fierce winds, and, like the spiders from which they get their name, eventually consume their companions. Black widow pulsars may be the missing link in the creation of single millisecond pulsars — those that rotate hundreds to thousands of times a second but lack a neighboring star to lend them the angular momentum to do so. In a new article, a team led by Roger Romani (Stanford University) used images and spectra to study the first known black widow pulsar, PSR J1959+2048. The image above (click for the full view) reveals the shock created by the pulsar’s outflowing wind colliding with interstellar material. Romani and collaborators used this rare sight — there are only nine known pulsar wind nebulae with associated shocks — to begin the investigation into whether this pulsar will lose too much energy to fully consume its companion. To learn more about this unusual object, check out the full article below!

Citation

“The Bow Shock and Kinematics of PSR J1959+2048,” Roger W. Romani et al 2022 ApJ 930 101. doi:10.3847/1538-4357/ac6263

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