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Lagoon and Trifid Nebulae

On 23 June 2025, the public got its first look at images from the NSF–DOE Vera C. Rubin Observatory — and the discoveries are already starting to roll in.

Trifid and Lagoon

Trifid Nebula closeup

A closeup of the Trifid Nebula from one of the Rubin Observatory first-look images. [Adapted from NSF–DOE Vera C. Rubin Observatory; CC BY 4.0]

One of the first-look images from Rubin features two photogenic star-forming regions in the Milky Way: the Trifid Nebula (Messier 20) and the Lagoon Nebula (Messier 8). The image, which was constructed from 678 exposures totaling 7.2 hours of observations, demonstrates Rubin’s ability to quickly cover large swaths of sky.

The Trifid and Lagoon nebulae are both HII regions, making them ideal places to search for circumstellar and protoplanetary disks, as well as proplyds — protoplanetary disks that are in the process of being evaporated by the intense radiation from nearby massive stars. The glowing gas of an HII region provides the background illumination needed to pick out the silhouettes of dark and dusty disks.

disk candidate

The Trifid Nebula disk candidate identified in this work. [Adapted from Zamani & Rector 2025]

Disk Detected

Published today in the Research Notes of the AAS, Mahdi Zamani (Zamani Scientific Visualizations & Imaging) and Travis Rector (University of Alaska Anchorage) reported the results of their search for proplyds in the Rubin image of the Trifid and Lagoon nebulae. The team detected one candidate circumstellar or protoplanetary disk on the edge of the Trifid Nebula, surrounded by tenuous, filamentary clouds of gas and dust.

The Rubin data don’t show evidence for ionized gas surrounding the disk, so it’s not yet clear if the object should be classified as a proplyd. The disk has a projected distance of 7.5 light-years from HD 164492A, the O-type star whose intense radiation is responsible for energizing the surrounding nebula, and may also be capable of ionizing the disk studied here.

Disk Detected

infrared image of the stars and protostars in the orion nebula

The Orion molecular cloud complex is among the most active star-forming regions in the Milky Way, home to hundreds of protostars and thousands of pre-main-sequence stars. [ESO/H. Drass et al.; CC BY 4.0]

This disk candidate is remarkable for both its size and location. With an estimated diameter of 4,000 au, it’s larger than most known circumstellar disks. Finding a disk outside the nearby Orion Nebula is also comparatively rare, since searches in more distant star-forming regions require finer resolution than the nearby Orion Nebula. (Orion is about 1,300 light-years away, and the Trifid Nebula is about 4,000 light-years away.)

Researchers have searched the Trifid Nebula previously for signs of protoplanetary disks, but while those searches found evidence for disks around hot stars near the center of the cluster, this particular disk candidate went undetected. Previous searches likely didn’t cover a large enough area of the nebula, or perhaps lacked the resolution needed to differentiate between the dusty disk and the nearby filamentary gas clouds. With Rubin’s broad field of view and precise resolution, the observatory was well-positioned to spot this disk candidate.

Citation

“The Potential Discovery of a Circumstellar Disk in M20 from Rubin First Look,” Mahdi Zamani and T. A. Rector 2025 Res. Notes AAS 9 172. doi:10.3847/2515-5172/ade982

Infinity Galaxy

Researchers have discovered a rare ring-galaxy duo that appears to harbor a supermassive black hole formed through direct collapse — a process similar to what may have jump-started the growth of the first supermassive black holes in the universe.

Searching for Oddballs

To find something remarkable, sometimes you have to go looking for it. As described in an article published today in the Astrophysical Journal Letters, a research team led by Pieter van Dokkum (Yale University; Dragonfly Focused Research Organization) recently struck gold in their search for unusual objects.

Van Dokkum and coauthors searched for interesting objects in publicly available images from COSMOS-Web, a JWST program dedicated to understanding how galaxies have evolved over the course of cosmic history. Having already published their discovery of a complete Einstein ring in the COSMOS-Web field, the team is now revealing a second finding: a galaxy featuring two bright, compact nuclei, two starry rings, and an unexpected inhabitant right in the center.

four views of the Infinity Galaxy

Four views of the Infinity Galaxy from Hubble and JWST. [van Dokkum et al. 2025]

Gathering Data

To learn more about this strange object, named the Infinity Galaxy for its resemblance to the infinity symbol, the team gathered data from the Hubble Space Telescope, the Keck I telescope, the Chandra X-ray Observatory, and the Very Large Array. The resulting multiwavelength portrait allowed the team to weigh the two nuclei, showing them to be massive — containing 80 billion and 180 billion solar masses of stars — and extremely compact. The new data also revealed that the cloud of gas between the nuclei contains a 1-million-solar-mass black hole.

The nuclei, the rings, and the gas between them appear to be the result of two disk galaxies that shot through one another, forming a pair of collisional ring galaxies. To achieve the infinity-symbol shape, the galaxies must have met one another face on, forming two parallel nucleus–ring systems that we see from an angle of about 40º. As the galaxies collided, some of their gas would have been torn away, left tangled together in the void between the two nuclei.

To the Infinity Galaxy and Beyond

radio and X-ray observations of the Infinity Galaxy

Radio (left) and X-ray (right) observations of the Infinity Galaxy, demonstrating that the black hole candidate is a strong radio and X-ray source. Click to enlarge. [Adapted from van Dokkum et al. 2025]

That explains the nuclei, the rings, and the gas between them — but where did the black hole come from? It’s possible that the black hole’s position between the two nuclei is simply a coincidence, either due to a chance alignment with an unrelated galaxy that hosts the black hole, or because the black hole happened to end up there after being ejected from one of the galaxies involved in the collision, or even from another galaxy that merged with the Infinity Galaxy.

The authors favor a different explanation, in which the location of the black hole is no coincidence. In this scenario, the colliding galaxies crushed a gas cloud between them so forcefully that the condensed gas collapsed directly into a black hole. The authors estimated that the collision happened 50 million years ago and created a 300,000-solar-mass black hole that subsequently grew to its current mass of 1 million solar masses. Direct collapse has been proposed to be a source of the seeds of supermassive black holes in the early universe, though there are some differences between the proposed process in the early universe and what may be happening in the Infinity Galaxy.

Van Dokkum and collaborators concluded their article by saying that future observations could clarify whether the black hole is truly associated with the Infinity Galaxy — and as reported in a press release today, preliminary analysis of follow-up observations with JWST show just that. With the black hole now definitively placed within the Infinity Galaxy, the evidence for direct collapse is strengthened, though more work is needed to probe this possibility.

Citation

“The ∞ Galaxy: A Candidate Direct-Collapse Supermassive Black Hole Between Two Massive, Ringed Nuclei,” Pieter van Dokkum et al 2025 ApJL 988 L6. doi:10.3847/2041-8213/addcfe

Falling into a supermassive black hole will leave a star mangled and destroyed but not without a fiery end. A recent study explores an intriguing case, uncovering new possibilities for stars lost to black hole bites.

Tidal Disruption Events

Invisible in light but strong in gravitational influence, some supermassive black holes reveal themselves when a star comes close enough to be ripped apart by the black hole’s tidal forces. This violent encounter produces a flare of radiation known as a tidal disruption event, allowing astronomers to explore the otherwise hidden properties of supermassive black holes and their influence on the material around them. 

Tidal disruption events vary depending on the properties of the host galaxy, the supermassive black hole, and the star itself. These events often appear as X-ray flares, but over the past decade, researchers have discovered a new class of optical-ultraviolet tidal disruption events. Emitting primarily in ultraviolet and optical wavelengths, these flares are significantly less energetic than predicted, leaving researchers wondering — what drives these disruptions?

Optical and ultraviolet light curves for the two observed flares of AT 2022dbl. The flares have very similar light curves across wavelengths. Click to enlarge. [Makrygianni et al 2025]

Origins of AT 2022dbl

New detections of optical-ultraviolet tidal disruption events can provide insights into their origins, and one such discovery is particularly intriguing. AT 2022dbl first flared in 2022 and emitted a second, nearly identical flare 700 days later in 2024 — behavior uncommon among this class of tidal disruption events — raising many questions about AT 2022dbl’s origins. Did this supermassive black hole perhaps capture two unrelated stars? Is this actually the same flare seen twice due to gravitational lensing? Could a single star have survived the first flare only to be disrupted again?

Lydia Makrygianni (Lancaster University) and collaborators performed follow-up imaging and spectroscopy of AT 2022dbl to probe how the two flares compare to each other and to other observations of optical-ultraviolet tidal disruption events. With these observations and detailed analysis, the team determined that gravitational lensing, the tidal disruption of two separate stars, and even the possibility of a hidden binary companion to the supermassive black hole slurping up some stellar crumbs each cannot account for the two flares of AT 2022dbl.

Ultimately, the authors concluded that the two flares of AT 2022dbl are related to the same star, leaving two possibilities. First, loose debris from the initial flare bound to a tidal tail around the black hole could have ignited the second flare; however, the authors found that there would not be enough loose material bound to the black hole to produce the bright second flare. Rather, the second and likeliest explanation is two repeated disruptions of the same star.

Disrupting Expectations

Light curves of AT 2022dbl flares compared to other optical-ultraviolet tidal disruption events. Both flares show similar peak luminosities and decline rates to other events. Click to enlarge. [Makrygianni et al 2025]

Assuming that the two tidal disruption events are from the same star, this implies that the first flare was a partial disruption, removing only some material without destroying the star entirely. The second flare could be a complete disruption or another partial disruption, but observations of a third flare in 2026 would be necessary to confirm this. 

Other optical-ultraviolet tidal disruption events appear similar to the flares of AT 2022dbl, and these have generally been assumed to be complete disruptions. With the discovery and classification of AT 2022dbl, the similar optical-ultraviolet tidal disruption events could also be partial disruptions, with their second flares on longer timescales yet to be observed. Future observations of optical-ultraviolet tidal disruption events are required to further understand the mechanisms driving them, and this study opens up new possibilities to consider. 

Citation

“The Double Tidal Disruption Event AT 2022dbl Implies that at Least Some ‘Standard’ Optical Tidal Disruption Events Are Partial Disruptions,” Lydia Makrygianni et al 2025 ApJL 987 L20. doi:10.3847/2041-8213/ade155

solar wind

Spacecraft scattered throughout the solar system keep tabs on the solar wind, but the measurements are dotted with data gaps. How can scientists prevent these gaps from biasing their studies of the solar wind?

Sampling the Solar Wind

intracluster medium

Left: the distribution of hot gas between the galaxies in the cluster Abell 2029. Right: the visible light from the galaxies in the cluster. [X-ray: NASA/CXC/UCI/A.Lewis et al. Optical: Pal.Obs. DSS]

The solar wind is a tenuous, fast-moving, turbulent plasma that constantly streams out from the Sun. Studying the solar wind is important for understanding how potentially damaging space weather events like coronal mass ejections travel through the solar system. Solar wind studies also have far-reaching implications, since solar-wind-like plasmas exist throughout the universe, such as in the sparse medium between galaxies in a cluster.

Luckily, there are many spacecraft that sample the solar wind from various locations within our solar system. Unluckily, many of these spacecraft do not continuously monitor the solar wind. For example, when a spacecraft orbiting a planet dips into the planet’s atmosphere, this detour creates an hours-long gap in solar wind monitoring.

The Impact of Data Gaps

How do these data gaps affect studies of the solar wind? In a recent research article, Daniel Wrench and Tulasi Parashar (Victoria University of Wellington) approached this question in terms of how gaps affect the structure function: a mathematical description of how the solar wind fluctuates over different length or time scales.

Wrench and Parashar introduced random artificial gaps into data from the Parker Solar Probe, which monitors the solar wind continuously, and compared the structure functions calculated from the continuous and interrupted data sets. They used the difference between the true structure function — calculated from the continuous data set — and the structure functions from the artificially gapped data sets to develop a correction factor.

bar plot of correction method performance

Performance of the correction factor method (black) compared to the uncorrected, gapped data (red) or gaps filled using linear interpolation (blue). MAPE is the mean absolute percentage error. [Wrench & Parashar 2025]

The team then tested their correction factor using data from the Wind spacecraft, which continuously monitors the solar wind from the L1 Lagrange point. The team calculated the structure function from 1) the continuous data set, 2) the artificially gapped data, 3) the gapped data with linear interpolation used to fill the gaps, and 4) the gapped data with the correction factor applied. This test showed that the correction factor performs better than other commonly used gap-handling methods, such as linear interpolation, which can systematically underestimate the structure function. Using the correction factor, the error in the structure function remained below 50% even when 95% of the data were missing.

plot of structure function from Voyager 1 data

Structure function calculated from uncorrected Voyager 1 data (red), linearly interpolated data (blue), and corrected data (black). Both the linear interpolation method and the correction factor method remove the artifact around a lag of 3×104 seconds, but the correction factor method does not suppress the signal like the linear interpolation method does. [Adapted from Wrench & Parashar 2025]

Correcting Voyager 1

Finally, the authors applied their validated method to data from Voyager 1. Data from the two Voyager spacecraft are extremely scientifically valuable — no other spacecraft have ventured as far from the Sun and can measure the solar wind at such large distances. The data are also extremely sparse; one segment used in this work was missing 85% of the data. This means that an effective method of correcting these data has potentially huge scientific significance.

Wrench and Parashar applied their correction factor to the Voyager 1 data, showing that this method handily removes artifacts while avoiding the underestimation introduced by linear interpolation. While the authors saved the interpretation of the newly corrected Voyager 1 data for future research, this study makes it clear that even large data gaps needn’t hinder studies of the solar wind.

Citation

“Debiasing Structure Function Estimates from Sparse Time Series of the Solar Wind: A Data-Driven Approach,” Daniel Wrench and Tulasi N. Parashar 2025 ApJ 987 28. doi:10.3847/1538-4357/addc6a

Illustration of Jupiter and a Jupiter-like exoplanet

Of the nearly 6,000 currently known exoplanets, few closely resemble any of the planets in our solar system. New research suggests that JWST is capable of directly imaging exoplanets with temperatures and orbital distances similar to Jupiter and Saturn, placing truly familiar exoplanets within our observational grasp.

Increasingly Cold Discoveries

Epsilon Indi Ab

A JWST image of the exoplanet Epsilon Indi Ab, one of the coldest exoplanets to be directly imaged. The planet’s temperature is estimated to be just 275K (35℉/2℃). [NASA, ESA, CSA, STScI, Elisabeth Matthews (MPIA)]

JWST has already proven itself to be a powerful tool to directly image exoplanet systems. The telescope has imaged increasingly cold planets, but the gas giants in our solar system are substantially colder than the coldest planet imaged by JWST so far. This raises the question of whether JWST is capable of directly imaging Jupiter and Saturn if they orbited another star.

Answering this question requires a deep dive into the abilities of JWST’s instruments. The current go-to method for directly imaging planets with JWST is coronagraphy with its Near-Infrared Camera (NIRCam). In this observing mode, the instrument blocks the light from the star, allowing the fainter thermal glow of the planet to shine through.

But as Rachel Bowens-Rubin (University of Michigan and Eureka Scientific) and collaborators note in a recent research article, this may not be the best way to detect cold giant planets. Models suggest that these planets have cloudy atmospheres, which means that they wouldn’t be bright at NIRCam’s preferred near-infrared wavelengths, and would instead be detected more easily in the mid-infrared, where JWST’s Mid-Infrared Instrument (MIRI) reigns.

Combining Data and Models

To examine the capabilities of both of these instruments, Bowens-Rubin’s team analyzed JWST observations from the Cool Kids on the Block program, which targets cold, low-mass giant planets around nearby low-mass stars with NIRCam coronagraphy and MIRI imaging. The team used observations of nearby M-dwarf stars Wolf 359 and EV Lac to construct constrast curves: the level of planet–star flux contrast that is detectable by each instrument as a function of distance from each star. These curves depend on the flux of the star and the planet as well as the limitations of the instrument — the detector noise and background noise.

plot of coldest planets detectable by MIRI and NIRCam

Temperatures of coldest detectable planets as a function of separation from the host star for Wolf 350 and EV Lac. Results are shown for MIRI F2100W imaging and NIRCam F444W coronagraphy. Click to enlarge. [Bowens-Rubin et al. 2025]

Bowens-Rubin and coauthors converted the contrast curves into information about the coldest planet each instrument can detect. To do this, the team modeled the atmospheres of planets with temperatures down to 50K and generated thermal emission spectra, which allowed them to relate the temperature of their modeled planets to the level of contrast.

NIRCam vs. MIRI

This analysis showed that MIRI is the best choice for directly imaging cold planets around nearby stars (within 65 light-years). MIRI should be able to detect giant planets with temperatures down to 94K around Wolf 359 and 114K around EV Lac — about the temperature of Saturn and slightly colder than Jupiter, respectively. For Wolf 359, sub-100K planets are detectable at orbital distances of at least 4.8 au, meaning these planets could also have similar orbital separations to Jupiter and Saturn.

plot coldest planets detectable by NIRCam and MIRI as a function of distance from Earth

Temperatures of planets detectable to a signal-to-noise ratio of 3 as a function of distance from Earth. Detection limits for MIRI and NIRCam are shown as red and blue lines, respectively. Click to enlarge. [Bowens-Rubin et al. 2025]

NIRCam coronagraphy can match MIRI’s performance only for the unlikely case of cloud-free giant planets; for cloudy planets around nearby stars, MIRI can spot planets 90–130K colder than NIRCam can. NIRCam has the advantage for more distant stars — beyond about 200 light-years — but only planets significantly warmer than Jupiter and Saturn are detectable at these distances.

As impressive as these results are already, Bowens-Rubin and coauthors noted that future work, such as developing strategies to mitigate MIRI’s “brighter-fatter effect” that limits sensitivity at small angular separations from the host star, could enhance the search for exo-Saturns and exo-Jupiters even further.

Citation

“NIRCam Yells at Cloud: JWST MIRI Imaging Can Directly Detect Exoplanets of the Same Temperature, Mass, Age, and Orbital Separation as Saturn and Jupiter,” Rachel Bowens-Rubin et al 2025 ApJL 986 L26. doi:10.3847/2041-8213/addbde

images from the Hubble Image Similarity Project

Motivated by a desire to support community members financially during the coronavirus pandemic, researchers employed 30 local citizen scientists in the Hubble Image Similarity Project. This project quantified the similarities between astronomical images, providing a way to test the results of image-search algorithms.

Seeking Similarities

Eagle Nebula

The Eagle Nebula, pictured here in an image from Kitt Peak National Observatory, is a star-forming region in the Milky Way. [T.A.Rector (NRAO/AUI/NSF and NOIRLab/NSF/AURA) and B.A.Wolpa (NOIRLab/NSF/AURA); CC BY 4.0]

Say you have an image of a star-forming region, featuring eye-catching gas clouds, dense and dusty knots, and newborn stars. How would you go about finding other images that resemble yours?

You might start your search with an astronomical image database, using filters for object type or instrument to sift through thousands and thousands of options. But even filtering out everything but star-forming regions might yield vastly different results, given the widely varying shapes, colors, and sizes of these regions.

Or maybe you’ll feed your image into a neural network that has been trained to spot similar images. The results may seem promising, but how can you tell whether the algorithm has found the images that are the most similar? Would another algorithm do better?

The Hubble Image Similarity Project

Astronomical image collections rarely contain information about similarities between images in their metadata, and while neural networks appear to excel at gathering similar images, the results of these models are generally unverified. The Hubble Image Similarity Project, led by Richard White (Space Telescope Science Institute) and Josh Peek (Space Telescope Science Institute and Johns Hopkins University), addressed these issues with a team of citizen scientists who generated similarity information for astronomical images, providing a quantitative means to test the results of neural networks.

example of how the Hubble Image Similarity Project selects image cutouts for study

An example of individual test images (green squares) extracted from a Hubble Legacy Archive image (red square). Low-contrast areas have been excluded, leaving the galaxy’s spiral arms for analysis. Click to enlarge. [White & Peek 2025]

White and Peek began by amassing a sample of images from the Hubble Legacy Archive. This sample included many different object types, such as galaxies, planetary nebulae, star-forming regions, and star clusters. After trimming and binning the images, converting them to 8-bit grayscale, filtering out low-contrast images, and eliminating satellite trails, image artifacts, and repeated observations of the same patch of sky, 2,098 images of 666 objects remained.

Citizen Scientists, Assemble

White and Peek recruited 30 members of the community within walking distance of the Space Telescope Science Institute to identify similar astronomical images, and the reviewers were paid for their work. In the three phases of the project, reviewers considered test images one at a time and 1) selected all similar images from a set of 15 comparison images, 2) selected the most similar image from a narrowed-down set of 6 comparison images, and finally 3) selected the most similar image from a set of 3 comparison images.

similar images from the Hubble Image Similarity Project and a visualization of the data

Examples of similar images according to the image similarity matrix. In the lower-right corner is a visualization of the similarity data. The semicircle of data points in the bottom half of this visualization represents galaxies, while star clusters occupy the small arc near the top and nebulae sit in the island in the center of the plot. Click to enlarge. [Adapted from White & Peek 2025]

The citizen science team ultimately compared 5.4 million pairs of images, and White and Peek used these comparisons to produce an image similarity matrix. The matrix describes the metaphorical “distance” between the images, with the most similar images being the smallest distance apart.

Similar images resemble one another in terms of structure, texture, and other factors that White and Peek say are “difficult even to describe in words” — for example, the diffuse glow of a galaxy interrupted by a bright star with diffraction spikes, or a nebula speckled with stars and dense dusty clumps. The similarity data from this study are available online and can be used to test the performance of image-search algorithms. In future work, the authors plan to carry out a similar project using images of the Martian landscape.

Citation

“The Hubble Image Similarity Project,” Richard L. White and J. E. G. Peek 2025 AJ 169 306. doi:10.3847/1538-3881/adcb43

While classic spiral and elliptical galaxies shine brightly, another class of galaxy flies under the radar. A recent study uses a new technique to search for galaxies so faint they are nearly completely dark.

Ultra-Diffuse Galaxies

Hard to see and harder to understand, ultra-diffuse galaxies are a galaxy class with extremely low surface brightness. With low luminosities but large physical extents, these galaxies appear as barely visible smudges, making them difficult to detect. Historically, astronomers have searched for ultra-diffuse galaxies using methods that search for diffuse stellar light; however, this method only catches those bright enough to spot — if even darker galaxies exist, they will not be found this way. Is there another way to discover these elusive galaxies?

Recent studies have shown that ultra-diffuse galaxies tend to have more globular clusters on average than typical galaxies. While this raises questions surrounding their formation and evolution, the abundance of globular clusters provides another way to search for ultra-diffuse galaxies. In general, globular clusters do not clump together in space unless there is additional mass, like dark matter, pulling them together. Thus, searching for overdensities of globular clusters could reveal a hidden population of ultra-diffuse galaxies.

Candidate Confirmation

Discovered as an overdensity of three globular clusters, Candidate Dark Galaxy-2 (CDG-2) was found in data from a Hubble Space Telescope (HST) program aimed at imaging the Perseus galaxy cluster. With an updated globular cluster catalog and improved statistical method for detecting overdensities, Dayi (David) Li (University of Toronto) and collaborators perform a follow-up search and analysis to confirm CDG-2 as a galaxy. Their method searches for clustering of globular clusters that do not appear to belong to any bright galaxy and are unlikely to be randomly grouped so closely in the intergalactic medium.

CDG-2

Euclid images of CDG-2 showing the four identified globular clusters (blue circles) and the faint diffuse emission (orange circles) associated with the galaxy. Click to enlarge. [Modified from Li et al 2025]

From their analysis, the authors find an additional globular cluster that belongs to CDG-2, making the object even more statistically likely to be a galaxy as opposed to four randomly clumped globular clusters. Further pointing to CDG-2’s galactic nature, two stacked HST images reveal a very faint light surrounding these globular clusters. To confirm that this diffuse emission is truly associated with CDG-2, the authors use data from Euclid, a space telescope that is optimized for detecting diffuse structures. The Euclid data confirm a low-surface-brightness fuzzy emission that coincides with the emission seen with HST and corresponds to the location of the four globular clusters — strong evidence that CDG-2 is indeed a galaxy.

Globular Cluster and Dark Matter Dominated

plot

Plot showing globular cluster total luminosity versus total galaxy luminosity for multiple galaxies. CDG-2 falls along the line corresponding to 16% of the total galaxy light coming from globular clusters. Click to enlarge. [Li et al 2025]

Further analysis of CDG-2 reveals that at least ~16.6% of its total light is contained within its globular clusters. However, if CDG-2 follows the typical distribution of globular clusters in galaxies and some are still undetected, this fraction could be as high as 33%, which would make CDG-2 have the highest globular cluster-to-stellar mass ratio of any galaxy to date. With additional analysis of the mass contained within the observed globular clusters, the authors estimate that CDG-2 is highly dark-matter dominated with 99.94%–99.98% of its total mass contained within dark matter. The dark-matter fraction could be even higher if CDG-2 contains more undetected globular clusters. Future observations of CDG-2 with deeper imaging and spectroscopy will more confidently determine the galaxy’s extreme and unique structure.

Through this study, the authors have confirmed the first galaxy ever detected solely through its globular cluster population. This technique opens a promising avenue to discovering more galaxies hiding out in the dark.

Citation

“Candidate Dark Galaxy-2: Validation and Analysis of an Almost Dark Galaxy in the Perseus Cluster,” Dayi (David) Li et al 2025 ApJL 986 L18. doi:10.3847/2041-8213/adddab

Messier 87 jet

M87 EHT image

The first detailed image of a black hole, M87*, taken with the Event Horizon Telescope. [Adapted from EHT Collaboration et al. 2019]

Messier 87, or M87, is a massive elliptical galaxy that hosts one of the best-studied supermassive black holes in the universe. The black hole, commonly called M87*, was the subject of the first-ever photograph of a black hole, which was released by the Event Horizon Telescope collaboration in 2019. Two years after that groundbreaking first photograph was revealed to the public, the collaboration released a set of polarized images of the black hole, illuminating the magnetic field conditions close to the black hole and fueling years of research since.

Today’s Monthly Roundup explores three aspects of this supermassive black hole: how fast it spins, the properties of its relativistic jet, and the source of its powerful flares.

Taking M87’s Black Hole for a Spin

Spin is one of the fundamental parameters describing a black hole, along with mass and electric charge, and it’s a challenging quantity to measure. In a recent research article, Michael Drew (University of Central Lancashire) and collaborators used data from the Event Horizon Telescope from 2017 and 2018 to measure the spin of M87*. Their goal was to measure the angular momentum of the innermost region of the disk of material swirling around the black hole. For a 10-billion-year-old black hole like M87’s, the angular momentum of the inner reaches of the accretion disk is fundamentally linked to the spin of the black hole.

Radial brightness profiles of M87*

Radial brightness profiles of the Event Horizon Telescope images of M87*. The variation of the brightness of the ring is due in part to Doppler beaming. Click to enlarge. [Event Horizon Telescope Collaboration 2019]

The team’s measurement technique hinges on the existence of relativistic Doppler beaming, which affects the apparent brightness of the fast-spinning material in the black hole’s accretion disk; material moving toward us as the disk rotates appears brighter, while material moving away appears fainter. By comparing the brightness of the brightest and faintest parts of the ring, Drew and coauthors estimated the velocity of the inner edge of the accretion disk. Combining this estimate with a measure of the disk’s inner radius from the Event Horizon Telescope yielded a measurement of the disk’s angular momentum and, by extension, the black hole’s spin.

This method returned a spin parameter of 0.8, which is within the broad range of previous estimates for M87*’s spin (0.1–0.98). Given certain assumptions made in this work, the team expects that this spin measurement is a lower limit on the black hole’s spin.

Closeup of Messier 87's relativistic jet

Closeup of Messier 87’s relativistic jet. [NASA and the Hubble Heritage Team (STScI/AURA)]

In addition to measuring the spin, the team also found a range of plausible accretion rates, from 4×10-5 to 4×10-1 solar mass per year (about 0.04–400 times the mass of Jupiter). These values are far below the theoretical maximum accretion rate for M87*, suggesting that while M87* is far more active than the black hole at the Milky Way’s center, it’s still fairly calm as far as black holes go. Finally, the team estimated the black hole’s accretion energy per unit time to be 6×1033–6×1037 Joules per second. These estimates largely overlap with existing estimates for the energy of M87*’s relativistic jet, supporting models in which the jet is powered by accretion.

A New Model for Bright-Edged Jets

One of the most dramatic features of Messier 87 is its prominent jet. Researchers have noted that M87*’s jet exhibits limb brightening, meaning that the jet appears brighter along its edges than in its center. This characteristic is present throughout M87*’s jet, from close to the point at which it’s launched to far down its length, and is also seen in other black hole jets.

simulation results showing that anisotropy results in a limb-brightened jet

Demonstration of limb brightening in models that include an anisotropic electron distribution. [Tsunetoe et al. 2025]

So far, simulations have succeeded in producing a limb-brightened jet under carefully tailored conditions, but they have not yet managed to produce this feature across a range of scales and black hole spins. A team led by Yuh Tsunetoe (Black Hole Initiative at Harvard University; University of Tsukuba) aimed to change that with their recent modeling study. The key feature of the team’s model is that the electrons that produce the jet’s prominent radio emission have much higher velocities parallel to the magnetic field lines that thread through the jet than perpendicular to the magnetic field (i.e., the electron distribution is anisotropic). Previous simulations using particle-in-cell methods, in which the behavior of individual particles is tracked, show that this anisotropic electron distribution is expected to arise in a relativistic, turbulent, magnetically dominated plasma.

Tsunetoe’s team used both general relativistic magnetohydrodynamics (GRMHD) and general relativistic force-free electrodynamics (GRFFE) in their modeling. These two modeling techniques have different strengths and weaknesses: GRMHD allows time variations to be studied, but is only effective close to the black hole, while GRFFE applies at a large distance from the black hole, but can only give a time-averaged result. By combining these two methods, the authors were able to generate synthetic radio-frequency images of M87*’s jet and compare them to observations.

simulated black hole jets

Simulated (left column) and observed (right column) jets. The top left shows the result from the GRMHD simulation and the bottom left shows the result from the GRFFE simulation. Note the difference in scale between the two simulations. Click to enlarge. [Adapted from Tsunetoe et al. 2025]

The resulting images show a clear limb-brightened jet across a wide range of both radio frequencies and spatial scales, as well as a striking resemblance to observations of the jet. In addition to comparing against existing data, Tsunetoe and collaborators produced images that can be compared against images from future facilities, such as the next-generation Event Horizon Telescope or the Black Hole Explorer. While more work remains to be done in the study of M87*’s jet — the team noted that their model doesn’t yet produce a counter-jet component as bright as what’s seen in observations — this work represents a significant advance in our ability to model the jets from supermassive black holes.

Investigating a Potential Source of Flares

Like many accreting supermassive black holes, M87* exhibits flares of high-energy radiation. These flares are highly variable, sometimes lasting only a couple of days, which suggests that they arise very close to the black hole’s event horizon. Precisely how these flares are generated is still unknown, though magnetic reconnection, in which magnetic fields rearrange and release pent-up magnetic energy, is a strong candidate.

Recently, Siddhant Solanki (University of Maryland) and collaborators investigated the source of M87*’s flares by tracing the paths of photons through a general relativistic magnetohydrodynamics simulation of an accreting spinning supermassive black hole. The simulation captured the region close to the black hole where magnetic reconnection is thought to occur, potentially launching electron–positron pairs that kick background photons up to high energies, powering a flare.

simulation of emission from M87* during a flare

Illustration of the origin of the simulated flare emission. The majority of the emission arises from very close to the black hole. The purple and cyan curves indicate magnetic field lines. [Solanki et al. 2025]

By charting the course of individual photons as they depart from the current sheet — the surface that separates magnetic fields of opposite direction — and navigate the magnetized plasma surrounding the black hole, Solanki and coauthors show that much of the flux from the simulated flares arises within just 5 gravitational radii of the black hole. This supports the hypothesis that quickly varying flares are generated near the black hole’s event horizon.

The timescales of the simulated flares were also instructive. While the simulated flares tended to last about 130 days, each flare was composed of multiple smaller subflares, which lasted roughly as long as the rapid, ~2-day flares seen from M87*. If these flares are truly subflares arrayed within a longer-duration flare, Solanki and collaborators noted, they should have different time variability at long and short wavelengths. This suggests a need for long-term, multiwavelength monitoring of M87* to clarify the source of its flares.

Citation

“New Estimates of the Spin and Accretion Rate of the Black Hole M87*,” Michael Drew et al 2025 ApJL 984 L31. doi:10.3847/2041-8213/adc90e

“Limb-Brightened Jet in M87 from Anisotropic Nonthermal Electrons,” Yuh Tsunetoe et al 2025 ApJ 984 35. doi:10.3847/1538-4357/adc37a

“Modeling of Lightcurves from Reconnection-Powered Very High-Energy Flares from M87*,” Siddhant Solanki et al 2025 ApJ 985 147. doi:10.3847/1538-4357/adcba9

Illustration of a planet around a red dwarf star

Which of the nearly 6,000 known exoplanets have atmospheres? New research suggests that small, rocky planets around the smallest and coolest stars are even less likely to hang on to their atmospheres than suggested by previous research. This result will help to guide the selection of target exoplanets for atmospheric characterization.

Approaching a Milestone

plot of the masses, orbital periods, and detection methods for currently confirmed exoplanets

Mass, period, and detection method for confirmed exoplanets as of 17 June 2025. Click to enlarge. [Exoplanet Archive/Caltech/NASA]

Today, the Exoplanet Archive reports that humanity has discovered 5,921 exoplanets, bringing us only a handful of detections away from the remarkable milestone of 6,000 known exoplanets. Though just a small fraction of the hundreds of billions to trillions of worlds estimated to occupy our galaxy, this planet sample is ripe for the search for atmospheres, habitable surfaces, and even life. But where to look?

When seeking planets with atmospheres, researchers must consider how a planet has fared in its lifelong battle between gravity and radiation. Massive planets orbiting calm stars are more likely to have atmospheres than lightweight planets around active stars. Astronomers define the cosmic shoreline as the dividing line between planets with atmospheres and planets without, in terms of escape velocity and the extreme-ultraviolet flux of the star.

Charting the Cosmic Shoreline

To predict on which side of the cosmic shoreline a particular planet lies, it’s not enough to know the current extreme-ultraviolet flux of its host star. A star’s extreme-ultraviolet flux changes over time, and integrating these changes over the lifetime of a planet yields its position along the shoreline. In a new research article, Emily Pass (Massachusetts Institute of Technology) and collaborators have suggested that this integration hasn’t been performed correctly for certain planets.

plot showing the rotation periods of M dwarf stars as a function of mass

Rotation periods of M dwarfs with masses less than 0.3 solar mass. The lack of M dwarfs with rotation periods between 9 and 50 days suggests a rapid transition between the two regimes. Click to enlarge. [Pass et al. 2025]

As stars age, they spin more slowly, and this slowdown is accompanied by a decrease in atmosphere-stealing stellar activity. For all stars down through early type M dwarfs, the slowdown is uniform, but research has shown that for mid-to-late M dwarfs, the transition from fast to slow rotation is sudden. Pass and coauthors suspected that this difference could impact how much radiation the planets of mid-to-late M dwarfs receive over their lifetimes.

Crossing the Line

Pass’s team estimated the flux of mid-to-late M dwarfs during two phases of their lives: the “saturated” phase, during which the stars rotate rapidly and their high-energy flux does not scale with their rotation rate, and the “unsaturated” phase, during which the high-energy flux declines as the rotation rate slows. The team consulted the literature to find the X-ray flux of M dwarfs during the two phases, then used a statistical approach to estimate how long the stars spend in each of these phases. The team also considered the impact of stellar flares as well as the stars’ lengthy pre-main-sequence phase, during which their overall luminosity is higher than it is once the star has fully contracted and begun its main-sequence lifetime.

positions of exoplanets relative to the cosmic shoreline

Previous and new positions of known exoplanets orbiting mid-to-late M dwarfs relative to the cosmic shoreline. Click to enlarge. [Pass et al. 2025]

Ultimately, these factors mean that it’s more challenging than previously predicted for planets around mid-to-late M dwarfs to hold on to their atmospheres. This recalculation even pushed some planets from one side of the cosmic shoreline to the other. The team also noted that certain planets still tagged as potentially having atmospheres may in reality be gaseous rather than terrestrial, highlighting the need for more work to characterize these worlds and guide the selection of target exoplanets for JWST and other sensitive telescopes.

Citation

“The Receding Cosmic Shoreline of Mid-to-Late M Dwarfs: Measurements of Active Lifetimes Worsen Challenges for Atmosphere Retention by Rocky Exoplanets,” Emily K. Pass et al 2025 ApJL 986 L3. doi:10.3847/2041-8213/adda39

Messier 81

New X-ray observations reveal the potential remnant of a dusty torus in the galaxy Messier 81. These observations help to advance our knowledge of low-luminosity active galactic nuclei, a population of accreting black holes that is still poorly understood.

Understanding Accretion

diagram of the unified model of active galactic nuclei

A diagram of the unified model of active galactic nuclei, showing an accretion disk, dusty torus, and jets. It’s not yet clear if LLAGNs conform to this model. [B. Saxton NRAO/AUI/NSF; CC BY 4.0]

Nearly all galaxies in our universe harbor a supermassive black hole. Many of these black holes are actively accreting matter from their surroundings, and these active galactic nuclei are powerful producers of radiation, winds, and jets. Roughly 40% of galaxies host a black hole that accretes matter at only a modest rate, which translates into a low-luminosity active galactic nucleus, or LLAGN.

Given how common it is for black holes to occupy this low-luminosity state, it’s critical to understand whether these systems are structured according to the typical picture of an active galactic nucleus, with a compact accretion disk surrounded by a dusty, donut-shaped torus. To probe the details of the LLAGN state, a team led by Jon Miller (University of Michigan) has turned to one of the best-studied — but still poorly understood — objects in this class.

Meet Messier 81

Just 12 million light-years away, the spiral galaxy Messier 81 is home to the nearest and brightest LLAGN. Messier 81’s central black hole was selected for observation during the 6-month Performance Verification phase of the X-ray Imaging and Spectroscopy Mission (XRISM), which launched in 2023. Messier 81 is the first LLAGN to be observed with a microcalorimeter, a type of instrument that detects photons by measuring minuscule changes in the temperature of the detector.

XRISM spectrum of Messier 81

XRISM spectrum of Messier 81’s nucleus (black line). The blue line shows the expected non-X-ray background. The bottom panel zooms in on the iron Kα line and several lines from highly ionized iron. Click to enlarge. [Miller et al. 2025]

Miller and collaborators focused on XRISM’s observations of several spectral lines from iron: the iron Kα emission line at 6.4 keV, which arises when neutral iron atoms in the vicinity of the active galactic nucleus reflect X-rays generated through accretion, and several emission lines from iron atoms stripped of all but one or two electrons.

Investigating a Diagnostic Line

The iron Kα line appears in the spectra of many active galactic nuclei, and it’s key to understanding whether LLAGNs like this one have the same accretion disk and torus structure as more vigorously accreting active galactic nuclei.

Modeling of the XRISM data suggests that the iron Kα line arises from material no closer than 27,000 gravitational radii from the black hole — a large distance compared to a typical compact accretion disk that closely rings the black hole. Miller and collaborators suggest that the likeliest explanation for the origin of the iron Kα emission is the remnant of a dusty torus that is only lightly obscuring the central accretion disk. This is in line with the hypothesis that LLAGNs are winding down from a higher-luminosity state, and that they maintain certain structures (i.e., a torus) from that highly active state as their accretion rate slows.

The team found that it’s also possible for the emission to arise from an accretion disk whose inner edge lies far from the black hole, in agreement with the predictions of an accretion model called radiatively inefficient accretion flow. The XRISM data didn’t place strong constraints on another possible accretion model, the magnetically arrested disk model. Future observations that either probe more deeply or attempt to detect variability could better illuminate the structure surrounding the black hole.

Fermi bubbles

Processing of data from the Fermi Gamma-ray Space Telescope reveals a dumbbell-shaped structure emerging from the center of the Milky Way. [NASA/DOE/Fermi LAT/D. Finkbeiner et al.]

Finally, a note about the emission lines from ionized iron: these might be due to a wind blowing outward from the accreting black hole, but Miller’s team suggests that they could also indicate the beginning of a feature similar to the so-called Fermi bubbles seen to extend on large scales from the center of the Milky Way.

Citation

“XRISM Reveals a Remnant Torus in the Low-Luminosity AGN M81*,” Jon M. Miller et al 2025 ApJL 985 L41. doi:10.3847/2041-8213/add262

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