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still images showing the results of two computer simulations of black hole accretion

We know that the supermassive black holes at the centers of galaxies can ensnare nearby gas and consume it; we see the doomed gas glow brightly as it advances toward the black hole. But exactly how a black hole’s meal makes its way toward the waiting gravitational maw isn’t clear. Are small gas clumps plucked at random from larger gas clouds, or does gas assemble into an orderly disk before falling into the black hole? In a recent research article, a team led by Minghao Guo (郭明浩) from Princeton University used fluid dynamics simulations to explore how gas accretes onto the supermassive black hole at the center of the massive elliptical galaxy Messier 87. The images above each show a region 6,500 light-years across that is centered on the supermassive black hole, with a zoomed-in 650-light-year region shown in the corner. The images show the two main pathways of cold gas accretion: chaotic accretion (left), which occurs only 10% of the time, and disk accretion (right), which is the dominant way for cold gas to be accreted. To learn more about the dynamics of gas accretion near a black hole, be sure to read the full article linked below.

Citation

“Toward Horizon-scale Accretion onto Supermassive Black Holes in Elliptical Galaxies,” Minghao Guo et al 2023 ApJ 946 26. doi:10.3847/1538-4357/acb81e

Images of dust emission from four nearby galaxies

Cosmic dust makes up just a small fraction of a galaxy’s mass, but it provides a useful way to study the interstellar medium: the gas and dust from which new stars and planets form. Using maps created from Herschel Space Telescope data presented in an earlier article, a collaboration led by Christopher Clark (Space Telescope Science Institute) studied the dust in the Large Magellanic Cloud, the Small Magellanic Cloud, the Andromeda Galaxy, and the Triangulum Galaxy (from left to right; not to scale). The three-color images above show hydrogen gas (red), cool dust (green), and warm dust (blue), highlighting how the dust density and temperature varies from galaxy to galaxy. The team used the new maps to study the galaxies’ dust-to-gas ratio — an important descriptor of the interstellar medium — and found that the ratio increased as the density of the interstellar medium increased. This trend might suggest that dust grains can bulk up more readily by nabbing material from the surrounding gas when the interstellar medium is denser. To learn more about the evolution of dust in our neighboring galaxies, be sure to check out the full article linked below.

Citation

“The Quest for the Missing Dust. II. Two Orders of Magnitude of Evolution in the Dust-to-gas Ratio Resolved within Local Group Galaxies,” Christopher J. R. Clark et al 2023 ApJ 946 42. doi:10.3847/1538-4357/acbb66

simulations of neutron stars merging

When a massive star ends its life in a supernova explosion, it can leave behind a tiny, dense remnant called a neutron star. Sometimes, two neutron stars end up locked in a gravitational embrace, emitting gravitational waves as they dance toward each other over millions of years. When the pair finally meets, their collision lights up the electromagnetic spectrum and creates heavy elements like gold and platinum. In a recent research article, Luciano Combi (Argentine Institute of Radio Astronomy, Perimeter Institute for Theoretical Physics, and University of Guelph) and Daniel Siegel (Perimeter Institute for Theoretical Physics, University of Guelph, and University of Greifswald) simulated the nuclear reactions and electromagnetic radiation produced after the merger of a pair of neutron stars. The image above illustrates four stages of their simulation, from the moment before the neutron stars meet, when their mutual gravity stretches them into teardrop shapes, to the merger aftermath, when an accretion disk feeds the sole remaining star. To learn more about the simulations described above, be sure to check out the full article linked below!

Citation

“GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process Nucleosynthesis and Electromagnetic Signatures of Dynamical Ejecta,” Luciano Combi and Daniel M. Siegel 2023 ApJ 944 28. doi:10.3847/1538-4357/acac29

simulation of the formation of the first stars

grid showing the simulation results for the particle number density under different values of rotation rate

Simulation results showing the number density of gas particles for 16 simulations with different values of β, which increases as the rotation rate of the cloud increases. Notice that the scale of the images changes as β increases. Click for high-resolution version. [Raghuvanshi and Dutta 2023]

When the first stars in the universe formed, ending millions of years of darkness, what masses did they have? This question is more than a matter of idle curiosity: if any of the first stars formed with masses less than 0.8 solar mass, they would still exist today. In a recent research article, Shubham Raghuvanshi and Jayanta Dutta (both from the Harish-Chandra Research Institute in India) performed hydrodynamic modeling to test how the rotation of a primordial gas cloud affects the resulting masses of the first stars. The images above and to the right show the results of their simulations after 50 solar masses of gas had been collected by the newly forming protostars. Ultimately, Raghuvanshi and Dutta found that in the fastest-spinning clouds, 10–12% of young stars might be ejected before they can grow past 0.8 solar masses. This suggests that if early gas clouds spun fast enough, some of the most ancient stars might still exist in modern galaxies, waiting to be found. To learn more about how the team modeled the making of the first stars, be sure to check out the full article linked below!

Citation

“Simulating the Collapse of Rotating Primordial Gas Clouds to Study the Possibility of the Survival of Population III Protostars,” Shubham P. Raghuvanshi and Jayanta Dutta 2023 ApJ 944 76. doi:10.3847/1538-4357/acac30

When a gas cloud collapses and fragments into stars, what masses do those stars have? The mass distribution of newborn stars in a cluster is called the initial mass function. While the initial mass functions of different star clusters appear to be similar, it’s still unclear as to whether certain factors, such as the abundance of elements heavier than helium (what astronomers call metals), can affect the mass distributions of stars when they’re born. To test the possibility that the abundance of metals affects the initial mass function, Chikako Yasui (National Astronomical Observatory of Japan) and collaborators searched the outskirts of the Milky Way for star clusters poor in metals, close enough that individual stars can be studied, and young enough that the stellar population still reflects the cluster’s initial mass function. The image above shows the team’s near-infrared observations of two suitable star clusters, which contain ~350 and ~1,500 stars each and are just 3 and 5 million years old, respectively. The team’s results suggest that these clusters might contain more high-mass stars than clusters rich in metals do, but further work is necessary to confirm this result. To learn more about this study, be sure to check out the full article linked below!

Citation

“Mass Function of a Young Cluster in a Low-metallicity Environment. Sh 2-209,” Chikako Yasui et al 2023 ApJ 943 137. doi:10.3847/1538-4357/ac94d5

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

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