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Earth

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

Earth Detecting Earth: At What Distance Could Earth’s Constellation of Technosignatures Be Detected with Present-day Technology?

Published February 2025

Main takeaway:

In a collaborative effort between the Search for Extraterrestrial Intelligence (SETI) Institute and the Penn State Extraterrestrial Intelligence Center, Sofia Sheikh (SETI Institute) and team turned inward to expand the search for intelligent life in the universe. Right here on Earth, humans have created a laboratory of technological signatures that can be detected from space — if another Earth-like civilization is out there, could they detect us? Using theoretical modeling, the authors determined the reaches of various human technosignatures such as radio transmissions, optical and infrared emission, satellites, and other probes sent into space. They found humanity’s strongest signals, radio transmissions, could be detected as far as 12,000 light-years away.

Why it’s interesting:

Scientists search for intelligent civilizations by hunting for signs of technology — signals or patterns that natural phenomena cannot explain. While we cannot expect other intelligent life to look exactly like Earth’s, many SETI projects have surveyed the skies for hypothetical signals far exceeding humanity’s own technological advancements. Taking a step back, Sheikh and collaborators considered where human technology is currently and what present-day instrumentation could pick up on if we were to search for ourselves. This “Earth detecting Earth” paradigm recenters the search for intelligent life and provides a multiwavelength framework for understanding the detectability of technology on far-away worlds.

Maximum detectability of Earth's technosignatures.

Maximum distances that Earth’s technosignatures could be detected by current technology. Click to enlarge. [Sheikh et al 2025]

Earth’s constellation of technosignatures:

What exactly are Earth’s many technosignatures, and how far could our current technology detect them? The most prominent and farthest detectable signal comes from radio transmissions. As the authors noted, these signals come from multiple sources: targeted radar transmissions used to characterize planets and asteroids, radio transmissions used to communicate between space probes and ground stations (e.g., space telescopes, Mars rovers, etc.), and radio leakage from Earth’s communication systems like cell towers and broadcasting stations. Additionally, there are atmospheric technosignatures from air-polluting compounds, optical and infrared emission from cities, targeted lasers from telescopes, and interplanetary and interstellar probes sent into space. All of these combined create a constellation of technosignatures detectable across a range of distances from Earth. This study underscores the importance of assessing Earth’s technology and detection capabilities, and repeating this type of study as technological advancements continue will enhance the search for intelligent life.

Citation

Sofia Z. Sheikh et al 2025 AJ 169 118. doi:10.3847/1538-3881/ada3c7

JWST image of the galaxy NGC 4141

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

FRB 20250316A: A Brilliant and Nearby One-Off Fast Radio Burst Localized to 13 pc Precision

Published August 2025

Main takeaway:

NGC 4141

MMT observation of NGC 4141 (left) and zoomed-in on FRB 20250316A’s location. The red lines show the 1-, 2-, and 3-sigma localization ellipses of the burst. Click to enlarge. [CHIME Collaboration 2025]

Discovered in March 2025 by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Outrigger array, FRB 20250316A is one of the brightest fast radio bursts ever observed. The CHIME collaboration traced the burst to the galaxy NGC 4141, 130 million light-years from Earth, and locked in on the source’s position with a precision of just 42 light-years.

Why it’s interesting:

The origins of fast radio bursts — bright flashes of radio waves lasting on the order of milliseconds — are mysterious, despite several thousand bursts having been cataloged. Among the many questions that remain is whether one-off bursts and repeating bursts arise from the same population of objects, or if they have entirely different origins. So far, FRB 20250316A appears to be a one-off burst; while it’s still possible that the source could emit another burst, the team noted that the burst’s properties don’t mesh with those of known repeating bursts. This makes the discovery and localization of FRB 20250316A an excellent opportunity to investigate the sources of one-off fast radio bursts.

More about the potential source of this burst, and prospects for pinpointing future sources:

After homing in on FRB 20250316A’s location, the CHIME collaboration embarked on a multi-wavelength follow-up campaign to learn more about where the burst came from. This campaign placed constraints on the metallicity and gas density near the source, which lies about 600 light-years from the center of the nearest star-forming region. A separate research article, published the same day as this work from the CHIME collaboration, described the discovery of a red giant star in the FRB 20250316A source region. This star may be located near FRB 20250316A’s source by chance, or it could be in a binary system with the source. With the main CHIME array in British Columbia continuing to scan for new bursts and three newly built outrigger telescopes in British Columbia, West Virginia, and California now online, we can expect many more precise localizations in the future!

Citation

The CHIME/FRB Collaboration: et al 2025 ApJL 989 L48. doi:10.3847/2041-8213/adf62f

illustration of the TRAPPIST-1 system

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e

Published September 2025

Main takeaway:

JWST spectra of TRAPPIST-1e

JWST spectra of TRAPPIST-1e (circles) and model outputs for several different atmospheric compositions and pressures (lines). Click to enlarge. [Glidden et al. 2025]

Ana Glidden (Massachusetts Institute of Technology) and collaborators used JWST to collect transmission spectra of the exoplanet TRAPPIST-1e. The team found evidence of stellar contamination in all of their observations, and they found that the data didn’t lean strongly in favor or against the planet having an atmosphere. Venus-like or Mars-like atmospheres were disfavored, hydrogen-rich atmospheres with traces of methane and carbon dioxide were excluded, and nitrogen-rich atmospheres with traces of methane and carbon dioxide were permitted.

Why it’s interesting:

TRAPPIST-1e is one of seven confirmed planets orbiting TRAPPIST-1, a cool M-dwarf star that is just larger than Jupiter and only 41 light-years away. All of these planets are roughly the size and mass of Earth, and as many as four of them — planets d through h — are thought to lie within the tiny star’s habitable zone. Thus, this system offers an excellent opportunity for powerful observatories like JWST to characterize the atmospheres of several potentially habitable planets. This study by Glidden’s team presents JWST’s first look at TRAPPIST-1e’s atmosphere through transmission spectroscopy.

How TRAPPIST-1 complicated the observations:

When examining an exoplanet that closely orbits its host star, special care must be taken to separate the signals from the planet and the star. This is especially tricky for active stars like TRAPPIST-1, whose surfaces are peppered with dark starspots and bright faculae. TRAPPIST-1’s surface features have contaminated observations of other planets in the system, as described in previous research, and these observations of TRAPPIST-1e were not exempt from the star’s meddling. Luckily, researchers are conducting further JWST observations that should help disentangle the star’s impact; an ongoing program will capture closely spaced transits of TRAPPIST-1e and TRAPPIST-1b, which trace nearly the same track across the star’s disk. Since TRAPPIST-1b appears to be a bare rock, any features that are shared between its spectrum and TRAPPIST-1e’s are likely to come from the star. Identifying these features will allow for better characterization of TRAPPIST-1e’s spectrum and atmosphere.

Citation

Ana Glidden et al 2025 ApJL 990 L53. doi:10.3847/2041-8213/adf62e

Bullseye galaxy

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

The Bullseye: HST, Keck/KCWI, and Dragonfly Characterization of a Giant Nine-ringed Galaxy

Published February 2025

Main takeaway:

Bullseye galaxy rings

Red ellipses overplotted on the first eight rings identified with Hubble in the Bullseye galaxy. Click to enlarge. [Pasha et al 2025]

Using a combination of the Hubble Space Telescope, the Dragonfly Telephoto Array, and the Keck Cosmic Web Imager, Imad Pasha (Yale University) and collaborators discovered and performed deep follow-up observations of a giant collisional ring galaxy aptly nicknamed the “Bullseye” galaxy (LEDA 1313424). The team identified a staggering nine rings in the Bullseye with a likely tenth that has since faded — the most rings found in any collisional ring galaxy to date. The rings are a result of a small blue dwarf galaxy shooting through the Bullseye’s core about 50 million years ago, sending ripples through the galaxy.

Why it’s interesting:

Galaxy mergers and interactions are commonplace in the universe, but it is very rare for a dwarf galaxy to strike right through a large galaxy’s core. When this does happen, the collision sends shock waves through the impaled galaxy, sweeping gas and dust outward and forming rings where star formation can occur (hence the name, collisional ring galaxy). These galaxies are valuable sites to explore galactic structure and evolution as well as provide a unique case to study galaxy mergers and interactions. Previously discovered collisional ring galaxies have at most two or three rings, so when Pasha and collaborators found the stunning nine in the Bullseye, it was clear they caught something significant.

Catching the Bullseye at a lucky time in its evolution:

Why does the Bullseye have so many rings? Theoretical studies of these head-on collisions predict that many rings will form and travel outward after the initial crash; however, the rings tend to dissolve after only a few hundred million years. Catching this collision only 50 million years after it happened means we are witnessing the earlier stages of the Bullseye’s evolution. This lucky discovery not only confirms theoretical predictions for collisional ring galaxies, it also may be a clue to how another unique galaxy type, giant low-surface brightness galaxies, originate. Given the wispy ring material found at very large radii from the Bullseye, the authors suggested that collisional ring galaxies may evolve into giant low-surface brightness galaxies as they expand outward and fade. Further investigation and a larger sample of collisional ring galaxies are necessary to confirm this hypothesis, but the Bullseye provides interesting and critical observational evidence of these predictions for the first time.

Citation

Imad Pasha et al 2025 ApJL 980 L3. doi:10.3847/2041-8213/ad9f5c

star-forming region AFGL 5180

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

The SOFIA Massive (SOMA) Star Formation Survey. V. Clustered Protostars

Published June 2025

Main takeaway:

A team led by Zoie Telkamp (University of Virginia) used the Stratospheric Observatory for Infrared Astronomy, SOFIA, to study massive protostars and test theories of high-mass star formation. Contrary to the predictions of some star-formation models, the team found no evidence that massive protostars require a certain surface mass density to form. Formation in a cluster environment, however, may limit the formation of the most massive protostars.

Why it’s interesting:

Massive stars are rare, short-lived, and luminous. They influence their environments across a vast range of spatial and temporal scales, from advancing the epoch of reionization in the early universe to impacting the formation of individual planetary systems in the present-day universe. The fundamental question of how high-mass stars form is still unsettled. Theories of high-mass star formation range from scaled-up versions of low-mass star formation to scenarios involving collisions between protostars.

More about this massive-star study and the potential impact of a cluster environment:

infrared images of massive protostars

SOFIA FORCAST and Herschel Space Observatory images of protostars in the G18.67+0.03 star-forming region. Click to enlarge. [Telkamp et al. 2025]

Researchers developed the SOFIA Massive Star Formation Survey to investigate the origins of massive stars, targeting roughly 50 high-mass and intermediate-mass protostars in a wide variety of environments in our galaxy. This particular work, the fifth in a series of articles reporting the survey’s findings, described the team’s study of massive protostars forming in cluster environments. Using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), Telkamp and collaborators identified 34 protostars in seven star-forming regions and estimated their masses and other physical properties. The team noted a lack of protostars above 30 solar masses in these cluster regions, which might be evidence that competition for gas in dense environments can prevent the formation of more massive protostars. More work is needed to confirm this finding.

Citation

Zoie Telkamp et al 2025 ApJ 986 15. doi:10.3847/1538-4357/adcd79

side-by-side images of galaxies

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

ImageMM: Joint Multi-Frame Image Restoration and Super-Resolution

Published September 2025

Main takeaway:

A team led by Yashil Sukurdeep (Johns Hopkins University) developed a new method for processing and combining ground-based astronomical images. The authors’ algorithm, called ImageMM because it leverages a method called majorization–minimization, yielded greater detail in bright sources and distinguished more faint sources from the background than existing methods.

Why it’s interesting:

As ground-based telescopes grow larger and their cameras grow more sensitive, they must still contend with one unfortunate fact: they are trapped beneath Earth’s atmosphere, which blurs fine details in astronomical images. To extract as much information as possible from beneath Earth’s blurry, ever-shifting atmosphere, researchers have developed numerous strategies for cleaning, combining, and sharpening astronomical images. From simple averaging of multiple exposures to complex statistical techniques, each of these methods has unique strengths and weaknesses. ImageMM succeeds in quieting background noise and sharpening images of both extended and point-like sources while avoiding many of the pitfalls of statistical methods.

How they tested the new method:

satellite-trail removal by ImageMM

An example of satellite-trail removal by ImageMM. Click to enlarge. [Adapted from Sukurdeep et al. 2025]

Sukurdeep and collaborators tested ImageMM on data from the Hyper Suprime-Cam on the 8.2-meter Subaru Telescope as well as on simulated images. These tests demonstrated not only that ImageMM can enhance the scientific value of noisy datasets, it can also handle interlopers like satellite trails and cosmic rays — and it processes data nearly in real time as it comes down the pipeline. This ability to rapidly and faithfully process high-resolution astronomical images will be critical for upcoming surveys, like the Vera C. Rubin Observatory’s 10-year Legacy Survey of Space and Time, which will generate immense amounts of data ready for processing.

Citation

Yashil Sukurdeep et al 2025 AJ 170 233. doi:10.3847/1538-3881/adfb72

extreme-ultraviolet image of the Sun

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

The Sun Reversed Its Decades-Long Weakening Trend in 2008

Published September 2025

Main takeaway:

plots of solar wind parameters from 2008 to 2025

Various solar wind parameters measured at Earth’s orbital distance from 2008 to 2025. [Jasinski and Velli 2025]

Jamie Jasinski (NASA’s Jet Propulsion Laboratory) and Marco Velli (NASA’s Jet Propulsion Laboratory and the University of California, Los Angeles) analyzed solar wind data from 2008 to 2025 and found that many solar wind parameters such as speed, density, temperature, and magnetic field strength increased over that time period. This increase ran counter to expectations that the Sun may be entering a historically low period of activity in 2008.

Why it’s interesting:

The Sun undergoes an 11-year activity cycle that is driven by a change in its internal magnetic field structure. As the Sun’s magnetic activity changes, the number of sunspots, the frequency of solar flares and coronal mass ejections, and the intensity of the solar wind vary as well. Atop these mostly regular 11-year changes are longer-term variations. A recent example of this longer-term behavior began in the 1980s, when an overall weakening trend was stamped upon the usual 11-year cycle. This decline led to an exceptionally deep solar minimum in 2008, leading researchers to suspect that the Sun’s activity level might remain low for decades.

The historical context for a prolonged weak period:

Though the Sun reversed its weakening activity trend in 2008, a prolonged period with little solar activity wouldn’t have been unprecedented. Astronomers have monitored and counted sunspots for centuries, allowing modern-day researchers to investigate the Sun’s behavior long before spacecraft began to study our home star. In the historical record, there are two instances of weak solar activity spanning multiple decades: the Maunder minimum in 1645–1715 and the Dalton minimum in 1790–1830. Compared to the 11-year solar cycle, these longer-term behaviors are more difficult to predict, and their causes are uncertain.

Citation

Jamie M. Jasinski and Marco Velli 2025 ApJL 990 L55. doi:10.3847/2041-8213/adf3a6

CHIME radio telescope

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

A Repeating Fast Radio Burst Source in the Outskirts of a Quiescent Galaxy

Published January 2025

Main takeaway:

FRB 20240209A localization region and likely host galaxy

Gemini-North image of the FRB 20240209A localization region (white lines) and the source’s likely host galaxy (cyan crosshairs). [Shah et al. 2025]

Using the Canadian Hydrogen Intensity Mapping Experiment (CHIME), Vishwangi Shah (McGill University) and collaborators discovered the repeating fast radio burst source FRB 20240209A. The team localized the source to roughly 130,000 light-years from the center of a quiescent elliptical galaxy about 1.8 billion light-years away. This suggests that the bursts originated from a globular cluster on the outskirts of the galaxy, pointing to a delayed formation pathway for the source.

Why it’s interesting:

Fast radio bursts are brief, intense flashes of radio waves from sources across the universe. Aside from one fast radio burst that has been associated with a magnetar within our own Milky Way, the source of these outbursts remains mysterious, and precise localization of these bursts is key to pinning down their origins; fast radio bursts that come from galaxies with active star formation may be linked to “prompt” formation channels like core-collapse supernovae or young magnetars, while bursts that arise in quiescent galaxies might be due to “delayed” formation pathways such as neutron stars that are born from merging white dwarfs.

How FRB 20240209A compares to other fast radio bursts, and what may have caused it:

FRB 20240209A is similar to other repeating fast radio bursts in terms of the shape of its individual bursts as well as its tendency to undergo periods of high and low bursting activity. Its location makes it quite unusual, though: it’s the only repeating fast radio burst known to come from a quiescent galaxy, and it’s the only burst — repeating or not — that has been found in an elliptical galaxy. If confirmed to originate from a globular cluster, FRB 20240209A would also be only the second known fast radio burst source to come from this type of environment. Shah’s team explored multiple possible origin stories for FRB 20240209A, including the possibility that the source was ejected from its host galaxy. The team favors an origin involving a magnetar formed through the collapse or merger of a compact object.

Citation

Vishwangi Shah et al 2025 ApJL 979 L21. doi:10.3847/2041-8213/ad9ddc

Messier 101 and SN 2023ixf

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

Search for Gravitational Waves Emitted from SN 2023ixf

Published May 2025

Main takeaway:

The LIGO, Virgo, and KAGRA collaborations searched for gravitational waves from the core-collapse supernova SN 2023ixf. Though no significant gravitational wave events were detected during times when two or more gravitational wave detectors were online, the non-detection of gravitational waves from this nearby supernova places constraints on the amount of energy emitted by the explosion in the form of gravitational waves, the shape of the proto-neutron star produced in the collapse, and more.

Why it’s interesting:

When a massive star expires in a core-collapse supernova, the collapse of the stellar core into a neutron star or black hole produces gravitational waves. These gravitational waves, along with a stream of neutrinos, should arrive at Earth before the light from the explosion does; gravitational waves and neutrinos can easily escape the dense, roiling ejecta from the explosion, but photons take some time to claw their way through the debris. Gravitational waves from a supernova have never been detected, but the nearby supernova SN 2023ixf, which occurred in a galaxy about 20 million light-years away, offered the best recent opportunity to detect these waves.

photometric evolution of SN 2023ixf and gravitational wave coverage of the event

Photometric evolution of SN 2023ixf in its early days and gravitational wave coverage leading up to the supernova’s discovery (inset image). [LIGO-Virgo-KAGRA Collaborations 2025]

What we learned from this non-detection:

Using the non-detection of SN 2023ixf, researchers placed stringent constraints on the gravitational wave energy and luminosity of a supernova explosion, but an even closer supernova is still needed to begin to rule out model predictions for these quantities. To estimate the distance out to which we can expect to detect gravitational waves from collapsing stars, the collaboration members injected synthetic supernova signals into their data. The majority of non-rotating explosions can be detected out to about 22,000 light-years — meaning events on the far side of our galaxy remain inaccessible to current detectors — while rapidly rotating explosions should be detectable out to nearly 100,000 light-years, pushing the detection horizon beyond the borders of the Milky Way.

Citation

A. G. Abac et al 2025 ApJ 985 183. doi:10.3847/1538-4357/adc681

3I/ATLAS

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

Hubble Space Telescope Observations of the Interstellar Interloper 3I/ATLAS

Published August 2025

Main takeaway:

3I/ATLAS

3I/ATLAS as seen by Hubble on 21 July 2025, when the comet was 3.83 au from the Sun. [Adapted from Jewitt et al. 2025]

David Jewitt (University of California, Los Angeles) and collaborators used the Hubble Space Telescope to observe the interstellar object 3I/ATLAS just a few weeks after it was discovered. These observations allowed the team to constrain the object’s mass-loss rate and the size of its nucleus, placing its radius between 0.22 and 2.8 kilometers.

Why it’s interesting:

3I/ATLAS is just the third known object to visit our solar system from another planetary system. With such a small sample size, every interstellar object discovered is a source of fascination. Are these objects more like comets or asteroids? How many of them roam the space between the stars? What, exactly, launches them into interstellar space? Using all available tools, including powerful observatories like Hubble, researchers can extract as much information as possible when interstellar objects make their brief journeys through our solar system, and get us closer to answering these key questions.

How these observations were planned, and what happened afterward:

After interstellar objects 1I/ʻOumuamua and 2I/Borisov zipped through the solar system in 2017 and 2019, respectively, researchers knew it was only a matter of time before the next interstellar interloper paid a visit. In preparation for the next arrival, Jewitt’s team proposed a target-of-opportunity observation with Hubble. This allowed them to disrupt the telescope’s planned observing schedule once 3I/ATLAS was discovered, getting an early high-resolution look that could guide further observations. Since then, researchers have published more than 30 articles in the AAS journals alone about 3I/ATLAS. In these articles, researchers have sought to understand where 3I/ATLAS came from, investigated its polarization properties, collected JWST data of the object, found it in pre-discovery data, and much more, crafting a comprehensive view of a rare visitor to our neighborhood.

Citation

David Jewitt et al 2025 ApJL 990 L2. doi:10.3847/2041-8213/adf8d8

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