Features RSS

little red dots

Among the discoveries JWST has made since its 2021 launch, “little red dots” are one of the most perplexing. Named for their compact size and red color, the origins of these distant galaxies remain unknown. A recent article explores some little red dots’ spectral energy distributions and local environments to better understand what may be lighting up these tiny torches.

Little Red Dot Dilemma

Along with their size and color, little red dots exhibit “V”-shaped spectral energy distributions (how they emit light across wavelengths), broad hydrogen emission lines, and no observed X-ray emission. These properties land them in an untapped parameter space with some similarities to both active galactic nuclei (AGNs) and stellar populations. Some previous investigations have suggested that little red dots contain AGNs, reddened by a dusty accretion disk scattering or blocking AGN light. Other studies have found that models for stellar populations can also fit certain little red dot spectra well. 

Adding to the ambiguity, observations and theory predict AGNs to show broad spectral lines, which are present in little red dots — but if little red dots are AGNs, this implies a much higher density of AGNs in the early universe than previously predicted by ground-based surveys. Furthermore, AGNs are expected to emit in the X-ray and show photometric variability, but neither property has been detected definitively thus far for a little red dot. With a clear dilemma arising for the origins of little red dots, astronomers are still prodding at these curious sources.  

AGN or Not?

AGN vs non-AGN fits

Comparison of AGN versus non-AGN fits using the Bayesian information criterion (BIC). Positive values of ΔBIC favor a non-AGN fit, and ~70% of little red dots have positive ΔBIC. Click to enlarge. [Carranza-Escudero et al 2025]

Leveraging the wealth of data available from recent JWST surveys, María Carranza-Escudero (University of Manchester) and collaborators built a sample of 124 little red dots spanning redshifts of z ~ 3–10. The authors used both AGN and non-AGN models to fit the spectral energy distribution for each galaxy. 

Using a robust statistical analysis, the authors found that AGN models tend to “overfit” the data — with more free parameters, an AGN model can be tweaked in a way that may not actually be physical (e.g., fitting for extremely high dust extinction that would not be possible). Instead, models without AGN components appear to be more appropriate for about 70% of the little red dots in their sample, suggesting that these peculiar objects may have a significant star-forming component powering their emission. 

environments histograms

Histograms for two redshift windows showing that little red dots (red) tend to be found in less dense environments than other galaxies (blue) in the same redshift window. Click to enlarge. [Carranza-Escudero et al 2025]

Lonely Neighborhoods

In addition to characterizing little red dots’ emission, the authors analyzed the local environments to compare to other galaxies at similar redshifts. From their analysis, they found that little red dots tend to be found in sparser environments, generally isolated from other galaxies. One explanation for this could be that little red dots in higher-density environments evolve past this peculiar stage faster, which is supported by observations of high-density environments accelerating the evolution of other galaxy types at similar redshifts. However, further investigation is required to better understand the connection between the local environment and little red dot properties. 

More little red dots are yet to be discovered, and continued analysis of their emission and environments will uncover more intriguing characteristics. For now, it seems as though little red dots are still a mystery.

Citation

“Lonely Little Red Dots: Challenges to the Active Galactic Nucleus Nature of Little Red Dots through Their Clustering and Spectral Energy Distributions,” María Carranza-Escudero et al 2025 ApJL 989 L50. doi:10.3847/2041-8213/adf73d

Beta Pictoris debris disk

JWST observations of a nearby star’s debris disk recently revealed what may be one of the lowest-mass planets ever imaged.

How to Find a Small Planet

Though it remains a formidable technical challenge, astronomers have gotten fairly good at taking images of planets around other stars by carefully blocking the light of the host and searching for the small points of light that remain. However, though this technique is well-suited for discovering large, bright, high-mass planets, their lower-mass cousins below the size of Jupiter remain challenging to detect. To get pictures of these smaller worlds, astronomers must resort to detective work and search for signs of their presence through indirect means.

One promising approach is to look not for the planet itself, but rather its effect on the dusty disk of material around the star. These structures, called debris disks, are constantly replenished by planetesimals colliding and grinding one another to dust. If a planet happens to orbit within this disk, it will “stir” the dust into distinctive patterns including rings and spiral arms. If astronomers observe that a star has a debris disk with gaps or spirals, they can analyze those substructures and deduce where a planet might be hiding.

The Star of this Show: TWA 7

TWA 7 debris disk and candidate planet

A mid-infrared image of TWA 7’s debris disk and candidate planet. [ESA/Webb, NASA, CSA, A.M. Lagrange, M. Zamani (ESA/Webb); CC BY 4.0]

TWA 7 is a tiny M-dwarf star just over 100 light-years from Earth. Data from the Spitzer Space Telescope revealed that TWA 7 was unusually bright when observed at infrared wavelengths, which hinted that there might be a warm, dusty disk surrounding the star. Follow-up observations with the Hubble Space Telescope and several major ground-based facilities confirmed that this star successfully met all the conditions listed above: TWA 7 is surrounded by a face-on debris disk with rings and a faint spiral arm. Using all of this information, astronomers predicted that a Saturn-mass planet might lie in a low-density pocket of the disk just beside the star.

This prediction led to a search with JWST last summer. Initial observations taken at mid-infrared wavelengths revealed a bright dot sitting near the predicted location of the planet. However, with just these observations, it was hard to confidently say that this source wasn’t just a distant background galaxy that happened to appear there by chance. To help settle the matter, JWST took another look in two different near-infrared wavelength bands a few weeks later.

JWST observations of TWA 7

New JWST observations of TWA 7. The sources labeled C5 and C6 are planet candidates. C6 is located at the same place as the planet candidate identified in mid-infrared observations, making it a strong candidate. C5 requires further observations to understand if it is real or an artifact. Click to enlarge. [Crotts et al. 2025]

Revisiting TWA 7

A team led by Katie Crotts (Space Telescope Science Institute) recently published these later observations. These new data show a dot in the exact same place as before, and with a color that’s much more planet-like than galaxy-like.

While this adds plenty of evidence to the planetary interpretation, the team cautions that one more set of follow-up observations is needed to be confident that this is, in fact, a planet. Assuming future observations back up these first hints, however, this would be the lowest-mass planet ever imaged, and a happy conclusion to a detective story that started with dust.

Citation

“Follow-Up Exploration of the TWA 7 Planet–Disk System with JWST NIRCam,” Katie Crotts et al 2025 ApJL 987 L41. doi:10.3847/2041-8213/ade798

JWST images of Earendel

What’s the nature of the distant source Earendel, which appears as a point of light in a dramatically gravitationally lensed galaxy?

Record-Breaking Discovery

Hubble image of the Sunrise Arc and Earendel

Hubble image zooming in on the Sunrise Arc and Earendel. The two images of the mirrored star cluster are called 1a and 1b. [NASA, ESA, Brian Welch (JHU), Dan Coe (STScI); Image Processing: Alyssa Pagan (STScI)]

In 2022, astronomers using the Hubble Space Telescope reported the discovery of the most distant single star candidate ever seen, now pinpointed to have a redshift of z = 5.926. The star, named Earendel, is an incredible beacon from the first billion years of the universe, standing out brilliantly from the red smear of its host galaxy, the Sunrise Arc.

But there’s a catch — at the distances involved, distinguishing between one star and many isn’t easy, and Earendel might not actually be just one star. New research uses stellar population modeling to explore the possibility that what has been touted as a single star is really a cluster.

The Light of Earendel, Our Most Beloved Star… Cluster?

The question sounds simple: does the light from Earendel resemble that of one star, or does it more closely align with the emission from a collection of many stars? What complicates matters is that Earendel’s light has been warped and magnified by an intervening galaxy cluster in a process called gravitational lensing. Because the degree of magnification isn’t known precisely, it’s not clear exactly how large the source is — leaving wiggle room for Earendel to be one or many stars.

JWST spectra of Earendel and 1b

JWST spectra of Earendel (top) and 1b (bottom), along with the best-fitting models. Click to enlarge. [Pascale et al. 2025]

To investigate Earendel’s identity, Massimo Pascale (University of California, Berkeley) and collaborators fit a simple stellar population model to JWST Near-Infrared Spectrograph (NIRSpec) spectra of both Earendel and another source in the Sunrise Arc called 1b, which is widely accepted to be a star cluster. The model varied the age of the cluster, its metallicity, the amount of dust it contains, and other factors. To make the modeling more rigorous, the team also used three different stellar population model libraries.

Both Earendel and 1b were well fit by all three stellar population models, supporting the hypothesis that Earendel is a cluster. Earendel and 1b share certain similarities, such as metallicity (less than 10% of the Sun’s), stellar surface density (high, rivaling the maximum density seen in the local universe), and age (more than 30 million years old).

Cluster Comparison

age and metallicity of star clusters in the nearby universe and at high redshifts

Metallicity and formation age of star clusters in the local universe, in the Milky Way and Magellanic Clouds, and at high redshifts. Click to enlarge. [Pascale et al. 2025]

Given the potential ages and metallicities of the two sources, it’s possible that both Earendel and 1b are the precursors to today’s globular clusters. These clusters may fit into an evolutionary sequence that connects other lensed star clusters, such as the redshift z = 10.2 Cosmic Gems clusters and the z = 1.4 Sparkler clusters.

While this work demonstrates that Earendel could be a cluster, it doesn’t prove that it is. Doing so is challenging, especially since certain features predicted to exist for a single star might be beyond our observational capabilities, or they could be reproduced by clusters with certain properties. The authors pointed to one smoking-gun signal for Earendel being a single, massive star: brightness fluctuations due to microlensing by stellar winds. So far, no such variability has been found, and the cluster hypothesis remains viable.

Citation

“Is Earendel a Star Cluster?: Metal-Poor Globular Cluster Progenitors at z ∼ 6,” Massimo Pascale et al 2025 ApJL 988 L76. doi:10.3847/2041-8213/aded93

An artist's impression of a planet beside a sun-like star.

By pushing JWST to its limits, astronomers may have just spotted a planet around the nearest Sun-like star, Alpha Centauri A. Though another look at the star is needed next year to confirm the finding, if the detection holds up, this discovery easily earns several superlatives: the planet would be the nearest, oldest, coldest, and lowest-mass world ever directly imaged beyond our solar system.

Hi, Neighbor!

The scale of our Milky Way galaxy is hard to comprehend with our Earth-bound minds that are more attuned to measuring distances in miles than in light-years. However, even though our suburban stellar neighborhood is tens of thousands of light-years from the galactic downtown, it is not empty: there are a handful of nearby systems that offer unique opportunities to study stars and their potential planet children “up close.”

An image of two bright stars atop many faint stars, with one faint star circled in red.

Alpha Centauri A and B (bright stars), along with Proxima Centauri, circled in red. [Wikipedia; CC BY-SA 3.0]

The nearest star system to the Sun at just over 4 light-years away is called Alpha Centauri. It’s a star “system” since what appears to the naked eye to be one star is actually three objects orbiting each other: Alpha Centauri A and Alpha Centauri B are two Sun-like stars that circle each other every 80 years or so, while Alpha Centauri C, better known as Proxima Centauri, circles the inner pair on a much wider orbit.

Though Proxima Centauri is the most famous of the trio, since it’s technically the closest star to the Sun, its larger siblings are arguably better targets for searching for planets. Since these stars are more massive, their habitable zones are large enough that astronomers can block out the star itself and search the surrounding area for planets using a tool called a coronagraph.

Challenging Observations

Back in 2019, a team of astronomers using a coronagraph on the Very Large Telescope uncovered tantalizing evidence of a giant planet orbiting Alpha Centauri A. However, confirming or rejecting this initial peek using telescopes on Earth’s surface was challenging. When JWST finally launched in 2021, following up on this hint was a top priority. Astronomers first attempted to point JWST toward the Alpha Centauri system in 2023, but unfortunately, the observations from that attempt were unusable.

Though one might think aiming a telescope at a nearby star is easier than taking a look at something more distant, this is unfortunately not the case. For one thing, the stars of the Alpha Centauri system are bright enough to overwhelm JWST’s sensitive detectors without careful calibration. For another, keeping the telescope locked on target and the star behind the coronagraph requires continuous tweaks to account for the Sun’s motion relative to Alpha Centauri, JWST’s motion relative to the Sun, and Alpha Centauri A’s motion relative to Alpha Centauri B. The team regrouped, tested a new observing strategy in mid-2024, then took three long observations in August 2024, February 2025, and April 2025.

A Planet Candidate

JWST coronagraph image of the Alpha Centauri system

JWST coronagraph image of the Alpha Centauri system. Alpha Centauri B is the bright labeled star at the top, while Alpha Centauri A is labeled but hidden behind the coronagraph. The inset shows the region around Alpha Centauri A during the three different observations. The planet candidate, labeled S1, is only visible in the August 2024 observation. Click to enlarge. [Beichman & Sanghi et al. 2025]

This time, the observations went off nearly without a hitch. After careful data processing, the team led by Charles Beichman and Aniket Sanghi of the California Institute of Technology found a bright blob positioned right beside the star in their August data. Interestingly, the blob disappeared in the next two observations. Working on the hunch that this blob was the same object as the planet candidate seen by the Very Large Telescope, the team realized that most allowed orbits would place the planet too close to the star to be visible in those later observations. In other words, the planet might be playing hide-and-seek, peeking out from behind the star in one month only to vanish in the next.

The authors estimated that the source is a 1–1.1 Jupiter radius planet with a mass of 90–150 Earth masses (0.28–0.47 Jupiter mass) on a 2–3-year orbit. The team stressed that with just one detection, this should still be regarded as a planet candidate, not a confirmed discovery. If the planet is eventually verified, however, it stands out among its peers as the first mature, cold planet ever imaged within its star’s habitable zone. Future detectors may be able to collect spectra of the planet itself, unlocking new insights into giant planet evolution and composition in multiple-star systems with nested orbits, like the Alpha Centauri system.

Now that JWST has a proven strategy for observing this challenging system, it should be possible to take follow-up images. If the planet is real and traveling on its expected orbit, it should reappear beside Alpha Centauri A in August 2026. Hopefully, JWST will be looking when it does, and we can finally confirm that we have a planetary neighbor next door.

Citation

“Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits,” Charles Beichman et al 2025 ApJL 989 L22. doi:10.3847/2041-8213/adf53f

“Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. II. Binary Star Modeling, Planet and Exozodi Search, and Sensitivity Analysis,” Aniket Sanghi et al 2025 ApJL 989 L23. doi:10.3847/2041-8213/adf53e

Current gravitational wave detectors are primarily sensitive to powerful sources like black hole–black hole mergers — what types of events may next-generation gravitational wave detectors reveal? A recent study explores stripped subgiant stars around supermassive black holes and how their gravitational waves may be detected in next-generation missions. 

Inspiraling Stars and Gravitational Waves

The immense gravity of supermassive black holes at the centers of galaxies drives complicated dynamics that could generate so far undetected gravitational wave signals. One predicted source of gravitational waves is a rare event known as an extreme-mass-ratio inspiral (EMRI) — a prolonged inspiraling of a stellar-mass object around a supermassive black hole, driven inward by gravitational waves. EMRIs are thought to arise when a stellar-mass object is captured into a close-in nearly circular orbit around a supermassive black hole, emitting gravitational waves due to the object’s proximity to the black hole. 

To date, most studies have explored EMRIs involving compact objects like black holes, but an EMRI with an inspiraling star is possible, though not yet well explored nor understood. In addition to generating gravitational waves, a stellar EMRI will also emit light as the supermassive black hole rips up siphoned material from the star. These events may explain recent observations of peculiar X-ray transients, but their gravitational wave counterparts remain undetected as EMRIs’ predicted signals fall outside the sensitivity range of current ground-based gravitational wave detectors. However, the Laser Interferometer Space Antenna (LISA), a space-based gravitational wave detector expected to launch in the mid-2030s, will be sensitive to the gravitational waves of EMRIs. In order to properly identify them, we must better understand what to expect.

Diagram showing the evolutionary steps of a supermassive black hole capturing a subgiant star that subsequently undergoes mass transfer and gravitational wave-driven inspiral. Click to enlarge. [Olejak et al 2025]

Modeling a Subgiant Inspiral

Seeking to better predict what the gravitational waves of stellar EMRIs may look like and what LISA may detect, Aleksandra Olejak (Max Planck Institute for Astrophysics) and collaborators used stellar evolution code to simulate the evolution of a subgiant star as it transfers mass to a supermassive black hole and gravitational waves draw in its orbit. In their models, the supermassive black hole captures the star through scattering between stars or tidal interactions with a stellar binary in which the black hole catches one star and ejects the other.

Once the star is captured, its orbit becomes circularized around the black hole, pulled in closer over time until mass transfer of the star’s outer envelope begins. During this stage, the gravitational wave signal remains too weak to be detected. However, as the star is stripped down to just a helium core, it contracts and experiences an extended gravitational wave–driven orbital decay.

Possible Detections with LISA

The strain spectral density as a function of the detected frequency of the gravitational wave. The colorful line indicates the signal from a stripped subgiant at the Milky Way’s center, and the gray lines are what would be observed at greater distances. LISA’s sensitivity to gravitational wave signals is shown with the black and red lines with detectable sources falling to the right of or above the line. Click to enlarge. [Olejak et al 2025]

With a better understanding of this process, the authors explored how such a signal compares to LISA’s sensitivity at various distances away from Earth. They found that as a star spirals inward, the gravitational wave signal grows stronger and enters LISA’s detectable frequency range. Stellar EMRIs occurring closer to Earth will result in higher signal-to-noise detections, and the gravitational waves from those occurring within the Milky Way would remain detectable for hundreds of thousands of years. The authors’ analysis revealed that, given their simulations, LISA could detect such an event out to ~3 billion light-years away. They estimate that a few systems involving similarly stripped subgiant stars could be detectable by LISA during a four-year mission, with a 1% chance of our galactic center hosting one.    

This study provides exciting potential for what is possible with LISA, and future detections of gravitational waves will shine further light onto the complicated dynamics of galactic centers and the evolution of stars around supermassive black holes.

Citation

“Supermassive Black Holes Stripping a Subgiant Star Down to Its Helium Core: A New Type of Multimessenger Source for LISA,” Aleksandra Olejak et al 2025 ApJL 987 L11. doi:10.3847/2041-8213/ade432

Illustration of an accreting supermassive black hole shrouded by dust

Astronomers have confirmed the discovery of a little red dot galaxy from when the universe was roughly half a billion years old. The galaxy, CAPERS-LRD-z9, is the most distant object to show the tell-tale broad emission lines of gas spiraling around a black hole, opening a new window onto black hole growth in the early universe.

Little Red Dots in the Spotlight

Images of six "little red dot" galaxies from JWST

Images of six “little red dot” galaxies from JWST. [NASA/ESA/CSA/I. Labbe]

Of all the discoveries JWST has enabled since its launch, none seems as enduringly mysterious as the tiny, distant galaxies nicknamed “little red dots.” These early universe objects are characterized by their small sizes, red color in JWST images, and V-shaped spectra.

But what are little red dots? Are they growing supermassive black holes busily amassing gas? Compact collections of old stars? Shredded stars spoon-feeding baby black holes? As reported today in the Astrophysical Journal Letters, new JWST data provide answers for one particularly distant dot.

JWST Takes Another Look

CAPERS-LRD-z9 was first identified as a possible high-redshift little red dot when it was observed by the Public Release IMaging for Extragalactic Research (PRIMER) survey with JWST’s Near-Infrared Camera (NIRCam). Anthony Taylor (The University of Texas at Austin) and collaborators followed up on the discovery with JWST Near-Infrared Spectrograph (NIRSpec) observations from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS). This spectrum pinned the object’s redshift at z = 9.288, corresponding to when the universe was only about half a billion years old.

With CAPERS-LRD-z9 placed along the cosmic timeline, Taylor and coauthors turned to the question of its identity. The JWST spectra revealed a broad emission line from hydrogen gas moving at thousands of kilometers per second — evidence that CAPERS-LRD-z9 harbors an accreting supermassive black hole (an active galactic nucleus or AGN) that is spinning gas into a frenzy around it. CAPERS-LRD-z9 is the most distant object known to show this characteristic signature of a growing black hole.

JWST spectrum of CAPERS-LRD-z9

JWST NIRSpec spectrum of CAPERS-LRD-z9 with the fit from the AGN (red) plus stars (blue) model. Click to enlarge. [Taylor et al. 2025]

Next, the team examined the little red dot’s spectral energy distribution, using a model that includes an AGN and a stellar population. To reproduce the step-like discontinuity seen in CAPERS-LRD-z9’s spectrum, they used a model in which the supermassive black hole is shrouded in a shell of dusty gas. The model fit well with a black hole mass of 38 million solar masses (though the authors estimate the mass could be anywhere in the range of 4.5–316 million solar masses), an upper limit of 1 billion solar masses on the stellar mass, and a gas density of 1010 per cubic centimeter surrounding the black hole.

Seeding a Black Hole

plot of black hole mass versus redshift for detected AGN and quasars

Observed black hole masses and redshifts of several sources, including CAPERS-LRD-z9 (large red star), quasars at redshifts of z > 6 (blue squares), massive spectroscopically confirmed AGN with broad emission lines (filled symbols), and the highest-redshift AGN detected to date via X-ray or ultraviolet emission. The shaded areas show the black hole masses achievable through accretion at the Eddington rate onto a massive (red) or stellar-mass (purple) seed. Click to enlarge. [Taylor et al. 2025]

Since successfully fitting one model doesn’t immediately rule out others, Taylor’s team also applied a stars-only model to the spectrum. This model fit poorly, and combined with the presence of broad hydrogen lines from fast-moving gas, this is strong evidence that CAPERS-LRD-z9 contains an accreting supermassive black hole.

This finding raises the question of how a black hole can grow to millions of solar masses in just 500 million years. The authors showed that this is possible in two scenarios: either the black hole began as a >10,000-solar-mass “seed” that grew at the Eddington rate — the hypothetical limit at which a black hole can accrete matter — or it started out as a smaller, ~100-solar-mass seed that grew at a super-Eddington rate. The observations rule out the possibility that the black hole grew from a ~100-solar-mass seed accreting at or below the Eddington rate.

In addition to setting the record for most distant broad-line AGN known, CAPERS-LRD-z9 gives new intel on the lives of black holes in the early universe. This won’t be the last we hear about this little red dot!

Citation

“CAPERS-LRD-z9: A Gas Enshrouded Little Red Dot Hosting a Broad-Line AGN at z = 9.288,” Anthony J. Taylor et al 2025 ApJL 989 L7. doi:10.3847/2041-8213/ade789

NGC 4151

Astronomers have known about NGC 4151’s X-ray-emitting active galactic nucleus since the 1970s. Now, observations from the X-Ray Imaging and Spectroscopy Mission (XRISM) show it in a whole new light.

Getting Feedback

illustration of active galactic nucleus winds

Illustration of the winds and accretion disk of an active galactic nucleus. [NASA, and M. Weiss (Chandra X -ray Center)]

Active galactic nuclei (AGNs) are extremely luminous galactic centers powered by accretion of matter onto a supermassive black hole. These nuclei provide a venue for galaxies and their supermassive black holes to interact. This interaction goes both ways, with the galaxy providing fuel to the supermassive black hole, and the AGN injecting material, momentum, and energy back into the surrounding galaxy in a process known as feedback.

AGN feedback can dramatically reshape a galaxy’s star formation and evolution. One of the most powerful ways an accreting supermassive black hole can influence its host galaxy is through ionized winds, which can scour the surrounding galactic bulge clear of star-forming material. There is much still to learn about these winds, including how they are structured and what physical processes drive them.

New Insights from XRISM

NGC 4151 provides an excellent opportunity to learn about active galactic nucleus winds. Only about 60 million light-years away, NGC 4151 hosts an accreting 34-million-solar-mass black hole that is luminous, highly variable, and shows a complex absorption spectrum that suggests that the AGN’s intense radiation is filtering through outflowing winds.

XRISM spectrum of NGC 4151

XRISM spectrum of NGC 4151, showing the multi-component model fit. Click to enlarge. [Xiang et al. 2025]

To study the winds of NGC 4151, a team led by Xin Xiang (University of Michigan) obtained X-ray spectra of NGC 4151 from XRISM on five dates spanning a period of about 6 months.

Xiang’s team modeled the array of absorption and emission lines in the XRISM spectra to tease out the properties of NGC 4151’s winds. They found that the best match to the spectra required up to six layers of absorbing material, showing that NGC 4151’s winds are highly structured. These absorbing layers took the form of slow warm absorbers (velocities between 100 and 1,000 km/s), very fast outflows (1,000–10,000 km/s), and ultra-fast outflows (10,000–100,000 km/s; up to one-third of the speed of light). While most of these components carry away mass as fast as or faster than the black hole accretes, some appeared to lack the oomph to escape the oncoming accretion flow, suggesting that they might be “failed” winds that curl back toward the AGN.

Being Blown Away

The data showed that the winds are likely magnetocentrifugally driven, meaning that material is lifted and accelerated from the surface of the disk along magnetic field lines as the disk rotates. For some of the wind components, especially warm absorbers emerging farther from the black hole, radiation pressure may be a driver as well.

Diagram of the multiple wind components of NGC 4151

Diagram of the wind components of NGC 4151, including ultra-fast outflows (UFOs), very fast outflows (VFOs), and warm absorbers (WAs). [Xiang et al. 2025]

Altogether, the modeling paints a picture of a complex, asymmetric, time-variable, and clumpy set of winds that carry significant mass away from the AGN. Several fast-moving outflow components appear to exceed the threshold luminosity necessary to blow star-forming gas out of the galactic bulge, suggesting that star formation in NGC 4151’s galactic bulge may someday be halted entirely by these winds.

Citation

“XRISM Spectroscopy of Accretion-Driven Wind Feedback in NGC 4151,” Xin Xiang et al 2025 ApJL 988 L54. doi:10.3847/2041-8213/adee9b

Crab Nebula

With a measurement 15 years in the making, astronomers have pinned down the path of a neutron star launched by a collapsing star. This finding helps to explain how neutron stars are “kicked” into space by supernovae.

Just for Kicks

Crab Nebula pulsar

This multiwavelength image shows the pulsar — a type of neutron star — at the center of the Crab Nebula supernova remnant. [X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech]

When massive stars reach the end of their lives, they expire in a final, fantastic cosmic display: a core-collapse supernova. These events can leave behind remnants called neutron stars, which are composed of highly compressed neutrons arranged in a sphere roughly as wide as the island of Manhattan is long.

Many neutron stars have been observed to zip through space at hundreds of kilometers per second, which suggests that these stars get a “kick” when they’re born in a supernova. However, the details of this kick are not yet clear. Are neutron stars launched into space in the opposite direction from the material ejected in the explosion, as some studies suggest? Or is the neutron star’s motion determined by the burst of neutrinos that carries off most of the supernova’s energy, as other studies hint?

Worth the Wait

To answer these questions, astronomers must compare the velocities of young neutron stars to the movement of their associated supernova remnants. In a recent research article, Tyler Holland-Ashford (NASA Goddard Space Flight Center) and collaborators measured the motion of the neutron star affiliated with the G18.9–1.1 supernova remnant, using Chandra observations made 15 years apart in September 2009 and July 2024.

Chandra images of the field containing the neutron star

Chandra images from 2009 (left) and 2024 (right; this image is the merged product of two observations). The neutron star is shown in black. Blue and red sources were used for astrometric correction. The red sources were present in both observations. Click to enlarge. [Holland-Ashford et al. 2025]

Making this measurement is trickier than it sounds, requiring more finesse than simply charting the location of the neutron star at different times. Holland-Ashford’s team used measurements from the ultra-precise star-mapping Gaia spacecraft to account for the proper motions of other sources in the images and to put the observations from the two time periods into the same frame of reference. After these adjustments, they measured the proper motion of the neutron star to be 24.7 milliarcseconds per year.

Because the distance to the supernova remnant is uncertain, this proper motion could correspond to a range of transverse velocities. For distance estimates of 6,800 and 12,400 light-years, this puts the neutron star’s transverse velocity at 264 or 474 km/s, respectively.

A Distinct Offset

supernova remnant and neutron star location

Current location of the neutron star (purple) compared to the geometric center of the supernova remnant (red) and the center of its X-ray emission (green). Even assuming the oldest reasonable age for the supernova remnant, there is a distinct offset between the neutron star’s birthplace and the center of the remnant. Click to enlarge. [Holland-Ashford et al. 2025]

What does this velocity tell us about the kick this neutron star received at birth? To probe the origin of the kick, the team first used the neutron star’s measured velocity and the likely age of the supernova remnant to trace the neutron star’s trajectory back to its birth site. This showed that the neutron star’s birthplace is offset from the center of the supernova remnant by several arcseconds, though both locations fall along the trajectory set by the neutron star’s motion. This suggests that the ejected stellar material and the newborn material were kicked in opposite directions by the supernova, most likely by a theorized “conservation-of-momentum-like” process.

Currently, Chandra is the only X-ray observatory with fine enough resolution to make the kind of measurement needed in this study. Luckily, Chandra’s observations of neutron stars stretch back to 1999, and combining this wealth of data with sensitive measurements from future high-resolution X-ray instruments should provide the long time baselines needed to trace the trajectories of more neutron stars and further explore the origins of neutron star kicks.

Citation

“Proper Motion of the Neutron Star in the Supernova Remnant G18.9–1.1,” Tyler Holland-Ashford et al 2025 ApJ 988 218. doi:10.3847/1538-4357/adeb7e

collage of multiple illustrations and images

There’s been a lot of astronomy in the news lately! Many recent news stories have featured research published in the AAS journals, so today we’re taking a look at four research articles that have recently gotten attention from the media.

New Horizons Navigates by the Stars

Starting closest to home, the first article describes a technological demonstration that took place on the edge of our solar system. In the nearly 20 years since its launch, the New Horizons spacecraft has ventured from Cape Canaveral to its current berth in the Kuiper Belt, roughly 61 au (5.7 billion miles or 9.1 billion kilometers) from Earth. In that time, New Horizons became the first spacecraft to venture close to Pluto and its moons as well as a second Kuiper Belt object called Arrokoth.

images of Proxima Centauri and Wolf 359 from New Horizons and from Earth

The difference in the position of Proxima Centauri (top row) and Wolf 359 (bottom row) as seen from New Horizons (left column) and Earth (right column) is evident by eye. [Adapted from Lauer et al. 2025]

New Horizons has also traveled a large enough distance for nearby stars to shift their positions relative to the background of more distant stars, enabling a measurement of the spacecraft’s position in space. Tod Lauer (NSF National Optical Infrared Astronomy Research Laboratory) and collaborators demonstrated this ability using New Horizons Long Range Reconnaissance Imager (LORRI) observations from April 2020, when the spacecraft was 47 au from the Sun. The stars used for the parallax measurements were Proxima Centauri and Wolf 359, two of the nearest stars to Earth. The team measured the stars’ positions relative to the positions of background stars and compared the results to observations made from Earth.

From the apparent shift in position of the two stars, the team determined the location of the spacecraft in space as well as the error in their measurement. They were able to ascertain the position of the spacecraft to within 0.44 au of its true position.

Though this measurement is far less accurate than localization with the Deep Space Network, it’s still an important step toward understanding the future prospects for autonomous spacecraft navigation via the stars. Looking ahead to future interstellar navigation systems, the team showed that measurements of a few nearby stars (Proxima Centauri and Barnard’s Star are the best bets for journeys within tens of thousands of astronomical units of the Sun) are more useful than measurements of a larger number of more distant stars. Basing measurements on a larger number of images to cut down on random scatter in the position of the star would also improve the results, as would simply using newer instruments. Ultimately, other types of navigation systems, such as those based on measurements of pulsars, are more likely to reach the precision necessary for autonomous spacecraft navigation. However, this method remains interesting, given that the straightforward nature of the imaging and analysis is already well within the capabilities of modern spacecraft systems.

First Detection of Semiheavy Water Ice Around a Low-Mass Protostar

Next up is a discovery from 457 light-years away in the Taurus molecular cloud. With a mass of 0.3–0.5 solar mass, a disk spanning 75–125 au, and a surrounding envelope of 0.9 solar mass, the isolated low-mass protostar L1527 is likely to grow into a star of similar mass to the Sun. That makes it an excellent target for investigating how planetary systems like our own acquire critical molecules like water.

Katerina Slavicinska (Leiden Observatory) and coauthors used JWST to search L1527 for semiheavy water (HDO) — a water molecule in which one of the hydrogen atoms is replaced with a deuterium atom. HDO has been detected in many locations throughout our solar system, including in Earth’s oceans, and water in our solar system tends to contain a high abundance of HDO molecules. A high deuterium abundance can be linked to formation in a cold environment, suggesting that our solar system’s water may have formed in the icy clouds out of which the Sun and the planets were born.

JWST spectrum of L1527

JWST spectrum of L1527. [Slavicinska et al. 2025]

Thanks to JWST’s high resolution and sensitivity, Slavicinska’s team was able to detect HDO ice in L1527, where previous, lower-resolution observations had only hinted at the presence of the molecule. They also measured emission from H2O ice, yielding a ratio of the abundances of the two types of water. The ice HDO/H2O ratio of L1527 is consistent with the gas HDO/H2O ratios of other isolated low-mass protostars and 4–7 times higher than the gas HDO/H2O ratios of clustered low-mass protostars.

plot of the ratio of semiheavy water to water for various solar system objects and protostars

HDO/H2O ratios for various solar system objects and protostars. Click to enlarge. [Slavicinska et al. 2025]

This difference may be due to differences in the star-forming environments of clustered protostars, or it may signal that the water in these protostars underwent gas-phase processing at some point. If environmental factors are the cause, that would suggest that L1527 should have a higher HDO/H2O ratio than objects in our solar system, since the Sun likely formed in a cluster environment.

This study demonstrates JWST’s ability to investigate the chemistry of young stars and probe the chemical evolution of protostars and planetary systems. Slavicinska and coauthors identified two important next steps to advance our understanding of the chemistry of star- and planet-forming environments: 1) measuring gas-phase and ice-phase HDO/H2O ratios in the same object to understand how gas-phase chemistry alters water around protostars and 2) measuring the HDO/H2O ratios of larger samples of isolated and clustered protostars in order to understand the impact of environmental factors.

A Massive Planet Approaches Its Doom

TOI-2109b is an ultra-hot Jupiter exoplanet that orbits its host star every 16 hours, giving it the shortest period of any known hot Jupiter. Orbiting its host star so closely, TOI-2109b is susceptible to powerful tidal forces that can lead to an exchange of angular momentum between the planet and its home star, potentially causing the planet to spiral inward and be engulfed by its star.

orbital periods, temperatures, and radii of ultra-short-period hot Jupiters

Comparison of the orbital period, temperature, and radius of TOI-2109b to other ultra-short-period Jupiters. [Alvarado-Montes et al. 2025]

Jaime Alvarado-Montes (Macquarie University) and collaborators investigated how and when TOI-2109b’s doom might come about. Critical to the discussion is the uncertain age of TOI-2109, which likely lies in the range of 1.09–2.65 billion years. If the star’s age is on the lower end of the range, TOI-2109b’s orbit would decay slowly (~4 milliseconds per year); if the star’s age is on the higher end of the range, the planet’s orbit would decay quickly (~1,100 milliseconds per year). The decay rate depends on the star’s age because planets lose their kinetic energy due to friction inside their host stars, and the efficiency of this process depends upon the interior structure of the star, which changes with age.

Alvarado-Montes and coauthors used data from the Transiting Exoplanet Survey Satellite (TESS), the CHaracterising ExOPlanet Satellite (CHEOPS), and multiple ground-based telescopes to constrain the rate of change of TOI-2109b’s orbital period. Taking into account changes in transit timing due to an outer planet candidate in the system, deviations from spherical symmetry, and other factors, the authors find a likely orbital decay rate of just 2.6 milliseconds per year. This is consistent with the rate predicted for a “young” host star, and it’s expected to shift TOI-2109b’s mid-transit time by a few seconds over a three-year period. This change is potentially detectable with high-cadence observations, helping to understand not just the fate of TOI-2109b, but of ultra-short-period planets as a whole.

Discovery of a Mysterious Long-Period Transient

Finally, Fengqiu Adam Dong (National Radio Astronomy Observatory; Green Bank Observatory) and coauthors recently described their discovery of an unusual long-period transient radio signal. Long-period radio transients exhibit signals that repeat with periods ranging from 10 seconds to multiple hours. While the exact origin of these signals remains unknown, researchers suspect that magnetic white dwarfs and neutron stars are the cause, with the two sources perhaps representing different classes under the long-period radio transient umbrella.

The signal was detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope, which was searching for bursts of radio emission from pulsars within our galaxy. The newly discovered radio signal, which comes from a source named CHIME J1634+44, has a primary period of 841 seconds and a secondary period of 4,206 seconds, making it decidedly un-pulsar-like. Dong’s team performed follow-up observations of CHIME J1634+44 with the Very Large Array, the Neil Gehrels Swift Observatory, and the Green Bank Telescope. The Very Large Array and the Green Bank Telescope each detected two bursts from the source, bringing the total number of bursts reported in this study to 89.

images of CHIME J1634+44

Continuum images of CHIME J1634+44 from the Very Large Array. The two panels show the autocorrelation function of the left-hand (left) and right-hand (right) circularly polarized components of the signal. CHIME J1634+44 is only detected in one of these two images, which suggests a 100% circularly polarized signal. [Dong et al. 2025]

CHIME J1634+44 is unusual in a number of ways. Its emission is almost entirely circularly polarized, meaning that the plane in which the electric and magnetic waves of the radio signal oscillates rotates in a circle as the signal travels through space. The time between pulses is also decreasing, slowly but steadily. If the pulsation period coincides with an object’s spin period, this means that the object is spinning faster as time goes on; this could occur if the source of the bursts is accreting material from a companion. If instead the pulsation period is linked to the orbital period of an object in a binary system, emission of gravitational waves could be causing the orbit to shrink.

What kind of object could produce this signal? Dong and coauthors considered binary systems containing either a white dwarf or a neutron star. Neither scenario perfectly fits the available evidence, but the team concluded that a binary system containing a neutron star is the likeliest source of the long-period, highly polarized, steadily accelerating pulses of CHIME J1634+44. The strongest evidence in favor of this scenario is that neutron stars are known to exhibit strongly polarized pulses of similar luminosity to those from CHIME J1634+44. Dong’s team expects that CHIME J1634+44 will remain an important test of theories of long-period radio transients — and as new information emerges about its identity, CHIME J1634+44 might just find its way into the news again!

Citation

“A Demonstration of Interstellar Navigation Using New Horizons,” Tod R. Lauer et al 2025 AJ 170 22. doi:10.3847/1538-3881/addabe

“HDO Ice Detected Toward an Isolated Low-Mass Protostar with JWST,” Katerina Slavicinska et al 2025 ApJL 986 L19. doi:10.3847/2041-8213/addb45

“Orbital Decay of the Ultra-Hot Jupiter TOI-2109b: Tidal Constraints and Transit-Timing Analysis,” Jaime A. Alvarado-Montes et al 2025 ApJ 988 66. doi:10.3847/1538-4357/ade057

“CHIME/Fast Radio Burst Discovery of an Unusual Circularly Polarized Long-Period Radio Transient with an Accelerating Spin Period,” Fengqiu Adam Dong et al 2025 ApJL 988 L29. doi:10.3847/2041-8213/adeaab

Through detailed simulations of gas and dust, a recent study revealed that the behavior of dust within protoplanetary disks is a bit more complex than previously assumed.

Dust Traps in Protoplanetary Disks

As a planet forms within a protoplanetary disk — dust and gas orbiting a new star — tidal interactions between the budding body and the dusty material surrounding it can create pressure bumps where dust builds up. These dust traps appear as rings in observations of protoplanetary disks.

Dust traps are thought to play a critical role in the disk’s evolution and the early stages of planet formation. Dust traps may prevent solid material from migrating inward, starving the inner disk and impeding planet growth interior to the trap. These reservoirs may also serve as a chemical barrier, keeping volatile materials like water from moving to the inner regions of a disk.

While a perfect dust trap completely isolates material from the rest of the disk, recent observations and 2D simulations have shown that dust traps may be a bit more permeable — leaking smaller sized grains, mixing material, and changing the disk’s appearance. However, these results only account for two dimensions of the complex three-dimensional environment in which dust traps reside. Thus, 3D hydrodynamical simulations are necessary to provide more realistic details of dust dynamics within planet-hosting protoplanetary disks. 

Dusty Simulations

Dust-gas density ratios for 3d models at 1500 orbits

Z-axis averaged dust–gas density ratios (top) and dust–gas surface density ratios for the 3D simulations after 1,500 orbits. For the simulations with higher diffusion and lower planet mass, there is clear leaking of dust beyond the dust trap ring (edges marked with dotted red lines). Click to enlarge. [Huang et al 2025]

In a recent study, Pinghui Huang (Chinese Academy of Sciences; University of Victoria) and collaborators performed multiple 2D and 3D numerical simulations of gas and dust within a protoplanetary disk with a forming planet. The simulations varied the mass of the planet and the level of turbulent diffusion — how well material and energy flow and mix within the gas. These variations allowed the authors to explore how dust traps behave within different types of systems. 

The simulations showed that the embedded planet will perturb the gas and dust, producing density shocks that create gaps and, subsequently, pressure bumps where dust traps coalesce. From their analysis, the authors found that dust traps become leakier at higher levels of diffusion and when the embedded planet is lower in mass. Essentially, if the gas flows and mixes more efficiently, the perturbations of the planet are erased more quickly, and if the planet is sufficiently small, its ability to disrupt the disk is much weaker. Dust remains coupled to the gas, flowing through these weak traps without becoming stuck. Additionally, the 3D simulations show higher amounts of leakage compared to the 2D simulations, which the authors attributed to the asymmetric and complex vertical geometry of the disk.

Trapping over time.

Flux-trapping ratio (left) and mass-trapping ratio (right) as a function of time for the 2D (top) and 3D (bottom) simulations. The higher-mass planet in Model A causes more flux and mass-trapping than the lower-mass planets and more turbulent systems. Additionally, the 3D simulations show significantly lower flux and mass-trapping than the 2D simulations. Click to enlarge. [Huang et al 2025]

Implications and Comparison to Observations

What then are the consequences of leaky dust traps? In planet formation theory, dust traps determine the mass at which a planet creates a sufficient pressure bump that isolates small pebbles and dust exterior to its orbit. For perfect dust traps, this isolation of material from the planet and inner disk creates a clear chemical distinction between the inner and outer disk. However, as shown by the 3D simulations, dust traps are imperfect, allowing small particles to filter through; the authors suggest this may mean that the growing planet slows but does not stop the migration of solid materials in a disk.

Recent observations of protoplanetary disks reveal the presence of larger volatiles within the inner disk. Specifically, the disk PDS 70 shows water emission in its inner disk despite having two confirmed giant planets orbiting in the outer disk. Without leaky dust traps, volatiles like water would be trapped in the pressure bumps created by these planets. However, as the authors have shown, the complex reality of dust dynamics within protoplanetary disks allows heavier elements to leak through, enriching the inner disk. Further observations and detailed 3D simulations will allow astronomers to understand the extent of leaky dust traps and reveal the realistic conditions driving early planet formation.

Citation

“Leaky Dust Traps in Planet-Embedded Protoplanetary Disks,” Pinghui Huang et al 2025 ApJ 988 94. doi:10.3847/1538-4357/addd1f

1 … 8 9 10 11 12 … 120