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starburst galaxy Messier 82

Starburst galaxies are prolific star factories, churning out tens to hundreds of stars each year. By contrast, the Milky Way crafts just a handful of stars annually. Recently, a team led by Alberto Bolatto (University of Maryland) turned JWST toward the cigar-shaped galaxy Messier 82, which is a starburst galaxy 12 million light-years away. Messier 82’s star formation rate has cooled from an impressive peak of 160 solar masses of stars per year 8–15 million years ago to 12 solar masses per year today. The team sought to study the powerful winds that whisk away star-forming gas from the galaxy’s center. In the image above, which shows the central few thousand light-years of the galaxy, red represents 3.3-micron (1 micron = 10-6 meter) emission that largely comes from polycyclic aromatic hydrocarbons: sooty molecules that contain multiple rings of carbon atoms bonded together. (Green and blue represent 2.5-micron and 1.6-micron emission, respectively; the compact green areas are mostly supernova remnants.) These new observations show in great detail the narrow, intertwined filaments and bubbles highlighted by the 3.3-micron emission. The filaments may have formed when dense, dusty clumps of gas were shredded by the outflowing galactic wind. To dive into the science behind this image, be sure to check out the full research article linked below.

Citation

“JWST Observations of Starbursts: Polycyclic Aromatic Hydrocarbon Emission at the Base of the M82 Galactic Wind,” Alberto D. Bolatto et al 2024 ApJ 967 63. doi:10.3847/1538-4357/ad33c8

snapshot of a simulation of gas outflows from the plane of a galaxy

When massive stars go supernova, their deaths can reshape their home galaxies. Using a high-resolution fluid dynamics simulation, Evan Schneider and Alwin Mao (University of Pittsburgh) examined how supernova explosions affect the distribution and temperature of a galaxy’s star-forming gas. Their simulations tackled how a galaxy similar to the cigar-shaped starburst galaxy Messier 82 evolves under the influence of supernovae. Synthetic star clusters scattered throughout the modeled galactic disk gradually warm their surroundings as they rotate in the plane of the galaxy, then suddenly inject large amounts of heat and energy when the stars explode. The image above shows a snapshot of the simulation after 30 million years of evolution, with red areas showing denser gas and blue areas showing more tenuous gas. Disrupted by stellar explosions, some of the disk’s gas flows into circumgalactic space, and Schneider and Mao found that the simulated outflow rate matches what has been estimated for nearby starburst galaxies. To learn more about this starburst galaxy simulation, be sure to check out the research article linked below.

Citation

“CGOLS V: Disk-Wide Stellar Feedback and Observational Implications of the Cholla Galactic Wind Model,” Evan E. Schneider and S. Alwin Mao 2024 ApJ 966 37. doi:10.3847/1538-4357/ad2e8a

Hubble Space Telescope images of three compact blue dwarf galaxies

The images above show three blue compact dwarf galaxies dotted with pink star-forming knots. Just a tenth of the size of the Milky Way, blue compact dwarfs are unique among galaxies with high star-formation rates in that they’re mostly free of dust and have low abundances of metals (elements heavier than helium) — properties they share with galaxies in the early universe. Using Hubble Space Telescope data, Rupali Chandar (University of Toledo) and collaborators investigated the star-formation histories of the three blue compact dwarfs pictured above. The team sought to understand whether these galaxies are all undergoing bursts of star formation, in which new stars are created at 10 times the usual rate. Their analysis revealed that while all three galaxies are forming plenty of new stars, only Haro 11 is truly experiencing a burst; ESO 185 was forming stars about four times faster than normal about 40 million years ago, and ESO 338 hasn’t seen much change in its star formation over the last few billion years. To learn more about the star-formation histories of these peculiar blue galaxies, be sure to check out the full research article linked below.

Citation

“A Tale of Three Dwarfs: Cluster-Based Star Formation Histories of Blue Compact Dwarf Galaxies,” Rupali Chandar et al 2024 ApJ 965 95. doi:10.3847/1538-4357/ad293a

14 different outputs from a supernova model

A research team led by Adam Burrows (Princeton University and the Institute for Advanced Study) has created the largest collection yet of state-of-the-art, three-dimensional core-collapse supernova simulations. The image above shows the results of several of the team’s simulations, showcasing the wide variety of structures and sizes attained by exploding stars just a few seconds after the stars’ outer layers rebounded off their collapsed cores. The smooth outer blue bubble shows the location of the expanding shock, while the more complex inner bubbles show the location of the ejected material. Red material is moving outward and blue material is moving inward. These simulations, which follow the collapse of stars with masses between 9 and 60 solar masses, allowed the team to find correlations between the properties of the explosions and the properties of the stars they came from. For example, the mass of the resulting neutron star is correlated with the compactness of the star. The simulations also predicted a correlation between the energy of the explosion and how asymmetrical it is, which can be tested in future studies. To learn more about the results of this study, be sure to check out the full research article linked below.

Citation

“Physical Correlations and Predictions Emerging from Modern Core-Collapse Supernova Theory,” Adam Burrows et al 2024 ApJL 964 L16. doi:10.3847/2041-8213/ad319e

star-forming region NGC 3603

The brightest giant star-forming region in the Milky Way has a new portrait, thanks to observations from a telescope flying through the stratosphere. A team led by James De Buizer (NASA Ames Research Center) paired new data from the airborne Stratospheric Observatory for Infrared Astronomy (SOFIA) with archival observations from the venerable Spitzer and Herschel infrared space telescopes to create the new image, shown above. The new observations yielded the highest-resolution data of the region at a wavelength of 25 microns (1 micron = 10-6 meter) and enabled the researchers to study star formation and search for structures around young stars. The clump of stars at the center of the image, HD 97950, is a starburst cluster that contains some of the most massive stars known. De Buizer’s team identified new massive young stellar objects, studied the dusty outflow of an evolved blue supergiant, and found several candidate high-mass proplyds: baby stars surrounded by dusty disks that are being blown away by intense radiation. To learn more about this enormous, dynamic star-forming region, be sure to check out the full article linked below.

Citation

“Surveying the Giant H II Regions of the Milky Way with SOFIA. VI. NGC 3603,” James M. De Buizer et al 2024 ApJ 963 55. doi:10.3847/1538-4357/ad19d1

map of matter in the universe, showing matter concentrations derived from measurements of the cosmic microwave background in grayscale and measurements of dusty galaxies in blue and orange contours

This image may look like a work of modern art, but it’s actually a map of the matter in our universe. A team led by Mathew Madhavacheril (University of Pennsylvania and Perimeter Institute for Theoretical Physics) developed this map from new measurements of the cosmic microwave background — the oldest light in the universe, which was emitted not long after the Big Bang. As this ancient light wends its way to us, it curves around the gravitational wells of intervening galaxies and galaxy clusters. By measuring the degree to which the microwave background is warped, researchers can determine how matter is scattered throughout the universe. The image above shows regions with lots of matter in white and regions without much matter in black. The orange and blue contours show the locations of dusty galaxies, which appear to be correlated with the location of matter measured from the microwave background. Researchers can test cosmological models with this new dataset, which covers nearly a quarter of the sky — the image here shows just a tiny fraction of the available data. To learn more about how researchers map matter and study structures in our universe, be sure to check out the original research article linked below.

Citation

“The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters,” Mathew S. Madhavacheril et al 2024 ApJ 962 113. doi:10.3847/1538-4357/acff5f

simulation results showing a variety of minidisk behaviors

From millions of light-years away, how can we tell if a galaxy contains one supermassive black hole or two? It’s a tricky problem: the gas around single supermassive black holes glows across the electromagnetic spectrum and varies on timescales from hours to years, and it’s not obvious how adding a second black hole changes these behaviors. As a step toward differentiating the two scenarios, a team led by John Ryan Westernacher-Schneider (Leiden University and Clemson University) simulated the gas surrounding pairs of black holes. When binary black hole systems ensnare gas from their surroundings, the gas collects in a large accretion disk around both black holes and in smaller disks around the individual black holes. These smaller disks are called minidisks. Each frame above shows a simulated minidisk with different physical parameters. Because of instabilities, the simulated minidisks sometimes become extremely elongated, and if future work suggests that this elongation is likely to happen in real disks, it may provide a way to interpret variations in the light from distant sources and pinpoint binary black holes. To learn more about these minidisk simulations, be sure to check out the full article linked below.

Citation

“Eccentric Minidisks in Accreting Binaries,” John Ryan Westernacher-Schneider et al 2024 ApJ 962 76. doi:10.3847/1538-4357/ad1a17

Two diagrams illustrating the radiation and particles generated by a kilonova

The image above shows the radiation and particles generated by a kilonova, the explosion produced when the remnants of two massive stars collide. Kilonovae made headlines in 2017, when scientists observed gravitational waves and a kilonova from colliding neutron stars for the first time. Recently, a research team led by Haille Perkins (University of Illinois Urbana-Champaign) used information gleaned from the 2017 event to estimate the threat posed by a kilonova’s X-rays, gamma rays, and cosmic rays. Fortunately for us, a kilonova would have to be quite close for life on Earth to be endangered by its X-rays or gamma rays — within about 3 light-years for X-rays or 13 light-years for gamma rays. Even after the initial glow of the collision fades, though, there’s still danger: high-energy charged particles called cosmic rays pose a threat years after the dangerous radiation has passed, and a kilonova’s cosmic rays can be lethal out to 36 light-years away. Luckily, kilonovae are extremely rare, and the danger to life on Earth is minimal. As researchers observe more kilonovae and improve their models, we’ll be able to refine our understanding of how close is too close when it comes to kilonovae, the threat they pose to Earth, and the role they play in determining where in the universe life can form and flourish.

Citation

“Could a Kilonova Kill: A Threat Assessment,” Haille M. L. Perkins et al 2024 ApJ 961 170. doi:10.3847/1538-4357/ad12b7

three side-by side images of galaxy clusters and lensed quasar images

three side-by side images of galaxy clusters and lensed quasar images

Hubble Space Telescope images of the three lensed quasars studied in this work. The multiple lensed images of the quasars are indicated by the cyan letters. [Napier et al. 2023]

How fast is the universe expanding? Currently, the measured expansion rate of the universe, described by the Hubble constant, depends on how you measure it, creating a clash of constants called the Hubble tension. The apparent disagreement between the rate measured from fluctuations in the cosmic microwave background — the oldest light in the universe — and the rate obtained from measurements of certain types of exploding stars suggests that either new physics is afoot, or these measurements are muddied by systematic errors.

Finding other ways to measure the Hubble constant may help alleviate the tension. In a recent article, Kate Napier (University of Michigan) and collaborators describe their derivation of the Hubble constant from observations of distant quasars: extremely luminous galactic centers in the early universe that are powered by matter falling onto a supermassive black hole. The quasars in the team’s sample are gravitationally lensed by clusters of galaxies, meaning that their light has been bent and magnified by the immense gravity of the clusters. The resulting value of the Hubble constant is consistent with measurements made from both the cosmic microwave background and supernovae, but the technique isn’t yet precise enough to favor one value over the other. To learn more about the use of lensed quasars for measuring the Hubble constant, be sure to check out the full article linked below.

Citation

“Hubble Constant Measurement from Three Large-Separation Quasars Strongly Lensed by Galaxy Clusters,” Kate Napier et al 2023 ApJ 959 134. doi:10.3847/1538-4357/ad045a

results of the Swift Deep Galactic Plane Survey

results of the Swift Deep Galactic Plane Survey

The plane of the Milky Way through the eyes of the Swift Observatory. Click to see a high-resolution version. [O’Connor et al. 2023]

Researchers often discover faint X-ray sources only by chance, when they happen to occupy the same field of view as a bright source under investigation. Recently, as described in a research article led by Brendan O’Connor (Carnegie Mellon University), the team behind the Swift Deep Galactic Plane Survey took a more purposeful approach to finding faint X-ray sources in our galaxy, spending a collective 22 days observing the plane of the Milky Way with the Neil Gehrels Swift Observatory to do just that. Bright galactic X-ray sources tend to be flaring X-ray binaries — neutron stars or black holes that siphon material from a companion star, creating a super-hot accretion disk — and faint X-ray sources are likely cataclysmic variable stars, or magnetars and X-ray binaries in their quiescent state. The images above and to the right give a broad view of the results of the survey, which led to the discovery of 348 previously uncatalogued X-ray sources. The team found many objects near the brightness limit of their survey, suggesting that even more sensitive telescopes are needed to fully understand the X-ray sources in our galaxy. To learn more about the Milky Way’s population of faint X-ray sources, be sure to check out the full article below for more information about the first phase of the Swift Deep Galactic Plane Survey.

Citation

“The Swift Deep Galactic Plane Survey (DGPS) Phase I Catalog,” B. O’Connor et al 2023 ApJS 269 49. doi:10.3847/1538-4365/ad0228

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