JWST Spies a Potential Microlensed Massive Binary Star System

The galaxy cluster MACS J0416.1-2403, as seen by the Hubble Space Telescope and JWST

Credit: Image: NASA, ESA, CSA, STScI, Jose Diego (IFCA), Jordan D'Silva (UWA), Anton Koekemoer (STScI), Jake Summers (ASU), Rogier Windhorst (ASU), Haojing Yan (University of Missouri); Image Processing: Joseph DePasquale (STScI)

JWST image of the gravitationally lensed Cosmic Gems arc, in which multiple individual star clusters are visible. Credit: ESA/Webb, NASA & CSA, L. Bradley (STScI), A. Adamo (Stockholm University) and the Cosmic Spring collaboration; CC BY 4.0

Glimpses of Single Stars

Galaxy clusters, the largest gravitationally bound structures in the universe, create the conditions necessary for astronomers to perform an extraordinary feat: examine individual massive stars and star clusters at far greater distances than our telescopes can typically achieve. This is possible thanks to gravitational lensing, the bending of spacetime by an immense mass, which warps and magnifies the light from more distant objects.

These glimpses of single stars and star clusters offer a rare chance to study massive stars in our universe’s distant past directly. In particular, these observations allow us to probe whether factors like the multiplicity fraction — how many massive stars are in binary or multiple systems — have changed over cosmic time.

The Warhol arc is the pinkish galaxy at the center of this image. Adapted from NASA, ESA, CSA, STScI, Jose Diego (IFCA), Jordan D’Silva (UWA), Anton Koekemoer (STScI), Jake Summers (ASU), Rogier Windhorst (ASU), Haojing Yan (University of Missouri); Image Processing: Joseph DePasquale (STScI)

Peering Through a Gravitational Lens

In a recent research article, a team led by Hayley Williams (University of Minnesota) reported on their examination of an intriguing source in a gravitationally lensed galaxy called the “Warhol arc.” This galaxy, located at a redshift of z = 0.94 (when the universe was roughly 6 billion years old), is gravitationally lensed by the massive galaxy cluster MACS J0416.1−2403. The cluster is located at a redshift of z = 0.396, corresponding to when the universe was about 9.4 billion years old.

Using data from the JWST Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS) program and the Canadian NIRISS Unbiased Cluster Survey (CANUCS), Williams’s team analyzed a source in the Warhol arc called W2, which previous work suggests is either a binary star system or a small star cluster.

Top row: The Warhol arc during four epochs of JWST observations. Bottom row: On the left, a magnified image of W2 during the first epoch. The remaining images show the difference in brightness between subsequent epochs and the first epoch. Click to enlarge. Credit: Williams et al. 2026

Multiplicity and Microlensing

Across four epochs spanning 126 days, the JWST observations show the source W2 within the Warhol arc. Williams and collaborators performed spectral fitting of the JWST light curves to investigate the multiplicity of the source. They found that the data are best matched by a binary system containing stars with temperatures of 3500K and 12600K.

W2 varies between observations in both brightness and color, a fact that the authors suggested is due to microlensing by a star within the lensing galaxy cluster, rather than variability within the binary system itself. Under this hypothesis, the orbital motions of the binary bring the stars across the microlensing caustic — a region in which the magnification is exceptionally high — and the brightness and color of W2 vary as the components of the binary approach and recede from the caustic.

Williams and collaborators also performed stellar population modeling to explore the binary configurations that could match the observations. They found that the stars likely have masses of 21–24 solar masses, with one being a cool red supergiant and the other a hot, main-sequence companion. Depending on the precise evolutionary stage of the binary, it’s possible that one of the stars is nearing a supernova explosion. Lending more support to the binary system hypothesis, the microlensing measurements constrain W2 to be no larger than 90 au — too small for even a compact star cluster.

The team closed by proposing further observations of W2’s position to rule out the possibility that the microlensing rate there is unusually high, an outcome that may suggest that microlensing of two unrelated stars, rather than a binary system, is responsible for these observations.

By Kerry Hensley

Citation

“JWST’s PEARLS: A Candidate Massive Binary Star System in a Lensed Galaxy at Redshift 0.94,” Hayley Williams et al 2026 ApJ 997 292. doi:10.3847/1538-4357/ae2003

Source: American Astronomical Society/AAS/Nova

---

NASA's Roman Could Bring New Waves of Information on Galaxy’s Stars

Red Giant Echoes with the Roman Space Telescope
Credits/Image: NASA, STScI, Ralf Crawford (STScI)

.

Red Giant Echoes with the Roman Space Telescope (Video)
Credits/Video: NASA, STScI
Sonification: Christopher Britt (STScI), Martha Irene Saladino (STScI)
Designer: Ralf Crawford (STScI) | Science: Noah Downing (OSU), Trevor Weiss (CSU)

---

A team of researchers has confirmed stars ring loud and clear in a “key” that will harmonize well with the science goals and capabilities of NASA’s upcoming Nancy Grace Roman Space Telescope.

Stars’ turbulent natures produce waves that cause fluctuations in their overall brightness. By studying these changes — a method called asteroseismology — scientists can glean information about stars’ ages, masses, and sizes. These shifts in brightness were perceptible to NASA’s Kepler space telescope, which provided asteroseismic data on approximately 16,000 stars before its retirement in 2018.

Using Kepler data as a starting point and adapting the dataset to match the expected quality from Roman, astronomers have recently proven the feasibility of asteroseismology with the soon-to-launch telescope and provided an estimated range of detectable stars. It’s an added bonus to Roman’s main science goals: As the telescope conducts observations for its Galactic Bulge Time-Domain Survey — a core community survey that will gather data on hundreds of millions of stars in the bulge of our Milky Way galaxy — it will also provide enough information for astrono mers to determine stellar measurements via asteroseismology.

“Asteroseismology with Roman is possible because we don’t need to ask the telescope to do anything it wasn’t already planning to do,” said Marc Pinsonneault of The Ohio State University in Columbus, a co-author of a paper detailing the research. “The strength of the Roman mission is remarkable: It’s designed in part to advance exoplanet science, but we’ll also get really rich data for other scientific areas that extend beyond its main focus.”

Exploring what’s possible

The galactic bulge is densely populated with red giant branch and red clump stars, which are more evolved and puffier than main sequence stars. (Main sequence stars are in a similar life stage as our Sun.) Their high luminosity and oscillating frequency, ranging from hours to days,work in Roman’s favor. As part of its Galactic Bulge Time-Domain Survey, the telescope will observe the Milky Way’s galactic bulge every 12 minutes over six 70.5-day stretches, a cadence that makes it particularly well suited for red giant asteroseismology.

While previous research has explored the potential of asteroseismology with Roman, the team took a more detailed look by considering Roman’s capabilities and mission design. Their investigation consisted of two large efforts:

First, the team members looked at Kepler’s asteroseismic data and applied parameters so the dataset matched the expected quality of Roman data. This included increasing the observation frequency and adjusting the wavelength range of light. The team calculated detection probabilities, which confirmed with a resounding yes that Roman will be able to detect the oscillations of red giants.

The team then applied their detection probabilities to a model of the Milky Way galaxy and considered the suggested fields of view for the galactic bulge survey to get a sense of how many red giants and red clump stars could be investigated with asteroseismology.

“At the time of our study, the core community survey was not fully defined, so we explored a few different models and simulations. Our lower limit estimation was 290,000 objects in total, with 185,000 stars in the bulge,” said Trevor Weiss of California State University, Long Beach, co-first author of the paper. “Now that we know the survey will entail a 12-minute cadence, we find it strengthens our numbers to over 300,000 asteroseismic detections in total. It would be the largest asteroseismic sample ever collected.”

Bolstering science for all

The benefits of asteroseismology with Roman are numerous, including tying into exoplanet science, a major focus for the mission and the galactic bulge survey. Roman will detect exoplanets, or planets outside our solar system, through a method called microlensing, in which the gravity of a foreground star magnifies the light from a background star. The presence of an exoplanet can cause a noticeable “blip” in the resulting brightness change.

“With asteroseismic data, we’ll be able to get a lot of information about exoplanets’ host stars, and that will give us a lot of insight on exoplanets themselves,” Weiss said.

“It will be difficult to directly infer ages and the abundances of heavy elements like iron for the host stars of exoplanets Roman detects,” Pinsonneault said. “Knowing these things — age and composition — can be important for understanding the exoplanets. Our work will lay out the statistical properties of the whole population — what the typical abundances and ages are — so that the exoplanet scientists can put the Roman measurements in context.”

Additionally, for astronomers who seek to understand the history of the Milky Way galaxy, asteroseismology could reveal information about its formation.

“We actually don’t know a lot about our galaxy’s bulge since you can only see it in infrared light due to all the intervening dust,” Pinsonneault said. “There could be surprising populations or chemical patterns there. What if there are young stars buried there? Roman will open a completely different window into the stellar populations in the Milky Way’s center. I’m prepared to be surprised.”

Since Roman is set to observe the galactic bulge soon after launch, the team is working to build a catalog in advance and provide a target list of observable stars that could help with efforts in validating the telescope’s early performance.

“Outside of all the science, it’s important to remember the amount of people it takes to get these things up and running, and the amount of different people working on Roman,” said co-first author Noah Downing of The Ohio State University. “It’s really exciting to see all of the opportunities Roman is opening up for people before it even launches and then think about how many more opportunities will exist once it’s in space and taking data, which is not very far away.” Roman is slated to launch no later than May 2027, with the team working toward a potential early launch as soon as fall 2026.

The paper was published in The Astrophysical Journal.

The Nancy Grace Roman Space Telescope is managed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation by NASA's Jet Propulsion Laboratory in Southern California; Caltech/IPAC in Pasadena, California; the Space Telescope Science Institute in Baltimore; and a science team comprising scientists from various research institutions. The primary industrial partners are BAE Systems, Inc. in Boulder, Colorado; L3Harris Technologies in Melbourne, Florida; and Teledyne Scientific & Imaging in Thousand Oaks, California.

To learn more about Roman, visit: https://www.nasa.gov/roman

Source: Space Telescope Science Institute (STScI)/Press Releases

---

About This Release

Credits:

Media Contact:

Abigail Major
Space Telescope Science Institute, Baltimore

Christine Pulliam
Space Telescope Science Institute, Baltimore

Permissions: Content Use Policy

Related Links and Documents

Noticias en español: El telescopio espacial Roman de la NASA podría aportar información nueva sobre las estrellas de la galaxia, PDF (406.55 KB)

---

Astronomers Find Far-flung “Super Earths” Are Not Farfetched

This artist's concept illustrates the results of a new study that measured the masses of many planets relative to the stars that host them, leading to new information about populations of planets in the direction of the bulge of the Milky Way. This study, published in the journal Science, shows that super-Earths are common and places them in context with gas giant planets. Credit: Westlake University

---

A new study shows that planets bigger than Earth and smaller than Neptune are common outside the Solar System

The same international team including astronomers from the Center for Astrophysics | Harvard & Smithsonian (CfA) has also announced the discovery of a planet about twice the size of Earth orbiting its star farther out than Saturn is to the Sun.

These results are another example of how planetary systems can be different from our Solar System.

"We found a 'super Earth' -- meaning it's bigger than our home planet but smaller than Neptune -- in a place where only planets thousands or hundreds of times more massive than Earth were found before" said Weicheng Zang, a CfA Fellow. He is the lead author of a paper describing these results in the latest issue of the journal Science.

The discovery of this new, farther-out super Earth is even more significant because it is part of a larger study. By measuring the masses of many planets relative to the stars that host them, the team has discovered new information about the populations of planets across the Milky Way.

This study used microlensing, an effect where light from distant objects is amplified by an intervening body such as a planet. Microlensing is particularly effective at finding planets at large distances – approximately between the orbits of Earth and Saturn – from their host stars. The largest study of its kind, this work has about three times more planets and includes planets that are about eight times smaller than previous samples of planets found using the microlensing technique.

The researchers used data from the Korea Microlensing Telescope Network (KMTNet). This network consists of three telescopes in Chile, South Africa, and Australia, which allows for uninterrupted monitoring of the night sky.

"The current data provided a hint of how cold planets form," said Professor Shude Mao of Tsinghua University and Westlake University, China. "In the next few years, the sample will be a factor of four larger, and thus we can constrain how these planets form and evolve even more stringently with KMTNet data."

Our Solar System consists of four small, rocky, inner planets (Mercury, Venus, Earth and Mars) and four large, gaseous, outer planets (Jupiter, Saturn, Uranus and Neptune). The searches for exoplanets to date using other techniques, i.e., transiting planet from telescopes like Kepler and TESS and radial velocity searches, have shown that other systems can contain a variety of small, medium, and large planets in orbits inside that of the Earth.

The latest work from the CfA-led team shows that such super-Earth planets are also common in the outer regions of other solar systems. "This measurement of the planet population from planets somewhat larger than Earth all the way to the size of Jupiter and beyond shows us that planets, and especially super-Earths, in orbits outside the Earth's orbit are abundant in the Galaxy" said co-author Jennifer Yee of the Smithsonian Astrophysical Observatory, which is part of the CfA.

"This result suggests that in Jupiter-like orbits, most planetary systems may not mirror our Solar System," said co-author Youn Kil Jung of the Korea Astronomy and Space Science Institute that operates the KMTNet.

The researchers are also looking to determine how many super Earths exist versus the number of Neptune-sized planets. This study shows that there are at least as many super Earths as Neptune-size planets.

Other CfA contributors to this study include post-doctoral fellow In-Gu Shin, former Harvard undergraduate student Hangyue Wang (now at Stanford), and Sun-Ju Chung, a KASI scientist who visited CfA on sabbatical from 2022-2023.

In addition to KMTNet, the Optical Gravitational Lens Experiment (OGLE) and Microlensing Observations in Astrophysics (MOA) survey groups contributed data for the planet characterization.

Source: Harvard-Smithsonian Center for Astrophysics (CfA)/News

---

About the Center for Astrophysics | Harvard & Smithsonian

The Center for Astrophysics | Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask—and ultimately answer—humanity's greatest unresolved questions about the nature of the universe. The Center for Astrophysics is headquartered in Cambridge, MA, with research facilities across the U.S. and around the world.

---