Young Giant Gas Planet Beta Pic b Refuses to Reveal its Origin

Young Giant Gas Planet Beta Pic b Refuses to Reveal its Origin
© ESO/L. Calçada

The GRAVITY instrument of the Very Large Telescope Interferometer (VLTI) at the European Southern Observatory’s (ESO) Paranal Observatory. © G. Rojas/ESO

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To the point

• Beta Pictoris b, atmosphere, origin: Researchers used the upgraded GRAVITY instrument (GRAVITY+) to study the atmosphere of Beta Pictoris b, a young giant gas planet, to understand its origin and atmospheric variability.


• Improved data, new findings: The updated GRAVITY data show a higher 12CO/13CO ratio than previous results, aligning with other studies and suggesting a lack of variance in the abundance ratio in the disc during planet formation.


• Atmospheric variability, rotation: There are tentative signs of atmospheric changes linked to Beta Pic b’s rotation period, possibly indicating clouds or chemical processes, but further observations are needed.


• Diagnostic tool doubts, isotope ratio limits: The consistent isotope ratios across many young gas giants and the interstellar medium challenge the use of carbon isotope ratios as reliable indicators of planet formation location.

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Results cast doubt on a seemingly reliable tool for inferring the origins of gas planets

The young and evolving planetary system of the 23-million-year-old star Beta Pictoris (short: Beta Pic) is regarded as an iconic circumstellar dust disc, which hosts at least three giant gas planets. Discovered already in 2008 by direct imaging, Beta Pic b is the most massive of those planets, measuring approximately 11 Jupiter masses. It orbits its host star on a wide trajectory, taking about 23 years for one revolution.

Astronomers from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, the Observatoire de la Côte d’Azur (OCA), Nice, France and others observed Beta Pic b to investigate the planet’s origin and potential atmospheric variability with the recently upgraded GRAVITY+ instrument. It is mounted to the Very Large Telescope Interferometer (VLTI), operated by the European Southern Observatory (ESO) at the Paranal Site in Chile. MPIA’s PhD student Antonia von Stauffenberg is the main author of the study published as a letter in the journal Astronomy & Astrophysics.

“The GRAVITY+ interferometric instrument is highly stable [...], making it uniquely capable of high-fidelity characterization of directly imaged exoplanets”, says co-author and MPIA scientist Jonas Sauter. GRAVITY+ is an upgrade of the original GRAVITY instrument, equipped with improved adaptive optics. What can we learn about Beta Pic b’s atmosphere and origin?

The team applied a method proposed a few years ago to identify a planet’s birthplace inside its planet-forming disc. By measuring the relative abundance ratio between two different versions of carbon (C) locked inside carbon monoxide (CO) gas in Beta Pic b’s atmosphere, it should be possible to infer whether the planet formed outside or inside a region in the disc where carbon monoxide was present as ice. Considering the irradiation by the host star heating the disc from its centre, this would directly translate to the distance from the star at which the planet formed. The radius at which the temperature is low enough to turn gas into ice is commonly referred to as the snowline.

The technical term for the different forms of an element, such as carbon, is an isotope. Isotopes exhibit the same number of positively charged protons in the nucleus of an atom, but differ in the number of neutral neutrons, like in the two carbon isotopes 12C and 13C. As a consequence, they have slightly different masses but exhibit similar chemical properties. In space, carbon is often found in association with oxygen, forming 12CO and 13CO molecules.

Exciting tentative scenario

Interestingly, in an earlier attempt to assess the diagnostic ratio between 12CO and the somewhat heavier 13CO, MPIA scientist Matthieu Ravet utilised the original GRAVITY instrument before its upgrade, yielding a comparatively low ratio. The authors already suspected that GRAVITY may have been inadequate to properly resolve the key signals in this dataset and advised caution in interpreting the results. Still, following the rationale of the scenario mentioned above, this face value suggests that Beta Pic b might have grown in the outer disc beyond the snowline by accumulating CO ice rather than CO gas.

However, at a range of about 10 au (astronomical unit = the mean distance between the Sun and the Earth; 1 au = 149.6 million km) from the host star, Beta Pic b currently circles the disc clearly between the star and the snowline, where CO should have been present predominantly as a gas. Assuming the result was correct, this finding would indicate Beta Pic b may have migrated through the disc.

New and better outcomes with GRAVITY

Using GRAVITY+, von Stauffenberg and her collaborators now derived an updated and more precise 12CO/13CO abundance ratio in Beta Pic b’s atmosphere, which is significantly higher than the earlier value. While 12CO is clearly detected and its content is straightforward to determine, measuring 13CO requires a more sophisticated approach. Interestingly, the ratio is consistent with the value reported in the companion paper by González Picos et al. (2026), who employed a different instrument. This demonstrates the improved data quality GRAVITY+ delivers compared to its original design. The previous GRAVITY result was clearly affected by systematic uncertainties.

In addition, the astronomers also found subtle hints that the observed levels of flux coming from the planet vary over time. Despite its low significance, the dominating variations seem to be linked to the planet’s rotation period of approximately 8.7 hours. If true, this may hint at clouds or chemical processes in Beta Pic b’s atmosphere. However, more sensitive observations are required to confirm the result.

Antonia von Stauffenberg says: “The ability to accurately constrain both isotopologues and potential rotational variability using ground-based observations of a bona fide planet such as Beta Pictoris b demonstrates the exceptional data quality achieved with the updated GRAVITY+ instrument.”

Doubting the significance of abundance ratios

In the proposed scheme to recover a gas giant’s birthplace, the new, more precise 12CO/13CO abundance ratio clearly shifts Beta Pic b into the warmer, inner range of the natal planet-forming disc, consistent with the planet’s current location. In addition, the ratio broadly matches values commonly found in the Solar System and the interstellar medium (ISM), which pervades the space between the stars in the Milky Way. The overwhelming majority of about a dozen young giant gas planets probed for the CO ratio show similar values.

This consistency may actually be bad news, because the carbon isotope abundance ratio doesn’t seem to be that diagnostic after all, when used as a probe to identify a planet’s distance from its host star. The most likely explanation is that any potential variance during planet formation is too small to be caught by the proposed method. This means that the 12CO/13CO ratio currently fails to be sufficiently decisive to tell us anything specific about individual planet-forming environments.
 

"It is still difficult to utilise 13CO as a formation tracer of giant planets, due to the uncertainties that still persist in the models and measurements."  Antonia von Stauffenberg, MPIA

Therefore, it is very likely astronomers are missing some crucial physics that govern CO ice chemistry in planet-forming discs. Thus, the 12CO/13CO ratio may not tell us much about the differences between the milder gaseous environments and the cold, CO-ice-laden realm after all. For now, it seems the wide-orbit giant gas planets refuse to reveal their origins. New tools that can distinguish between planet formation scenarios are needed, and GRAVITY+ may play a vital role in finding and evaluating them.

Additional information

The results are based on data obtained as part of the GRAVTY+ Guarantee Time Programme (GTO) 114.27JS (PI: Laura Kreidberg). The GRAVITY+ consortium includes the following institutes: MPE, INSU/CNRS, University of Cologne, MPIA, CENTRA, University of Southampton, and the associated partners KU Leuven, University College Dublin, and Universidad Autónoma de México, in close collaboration with ESO and supported by the Max Planck Foundation.

MPIA astronomers involved in this study were Antonia von Stauffenberg, Jonas Sauter, Paul Mollière, Matthieu Ravet (also at Observatoire de la Côte d’Azur, Nice, France [OCA] and Université Grenoble Alpes, Grenoble, France), David Trevascus, Wolfgang Brandner, Gaël Chauvin (also at OCA), Laura Kreidberg, and Elisabeth Matthews.

Other researchers were:

A. Berdeu (Observatoire de Paris, Meudon, France), M. Bonnefoy (Institut de Planétologie et d’Astrophysique de Grenoble, France), G. Bourdarot (Max-Planck-Institut für extraterrestrische Physik, Garching bei München, Germany [MPE]), J.-B Le Bouquin (Université Grenoble Alpes: Saint-Martin-d’Hères, Auvergne-RhôneAlpes, France [UGA]), F. Eisenhauer (MPE), M. Houllé (UGA), F. Millour (OCA), J. Scigliuto (OCA), J. Wang (Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, USA), J. W. Xuan (Department of Astronomy, California Institute of Technology, Pasadena, USA [Caltech] and Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, USA), Y. Zhang (Caltech), and the GRAVITY+ Collaboration.

The Very Large Telescope Interferometer (VLTI), operated by the European Southern Observatory (ESO), is an infrared interferometer that combines light collected by the four Very Large Telescope (VLT) 8.2-metre Unit Telescopes (UTs) or the four movable 1.8-metre Auxiliary Telescopes (ATs). The VLTI is located at ESO’s Paranal Observatory in Chile.

GRAVITY+ is an upgrade to the VLTI and its original GRAVITY instrument. It enables imaging of fainter and more distant astronomical objects than previously possible, while also improving high-contrast precision on bright objects. Its consortium consists of 15 research institutes from seven European countries, including MPIA and ESO.

Source: Max Planck Institute for Astronomy/Researche Reports

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Contacts:

Dr. Markus Nielbock
Press and outreach officer
Tel: +49 6221 528-134
Email: pr@mpia.de
MPIA press team
Max Planck Institute for Astronomy, Heidelberg, Germany

Antonia von Stauffenberg
Email: a-stauffenberg@mpia.de
Max Planck Institute for Astronomy, Heidelberg

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Original publication

A. von Stauffenberg et al.
13CO and potential variability in β Pictoris b with GRAVITY+
Astronomy & Astrophysics (2026)

Source | DOI

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Links

GRAVITY+ at ESO
GRAVITY+ at Max Planck Institute for Extraterrestrial Physics (MPE)
GRAVITY at ESO
GRAVITY at Max Planck Institute for Extraterrestrial Physics (MPE)

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Probing the host galaxy of one of the most distant quasars

Artist's impression of the early quasar with its starforming host galaxy.
© T. Müller, HdA/MPIA

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To the point:

• Super-effective distant quasar hunter: the ESA space telescope Euclid has found a treasure trove of early quasars, including two at record-breaking distances, and is poised to find many more.


• First look at ordinary early quasars: This is the first time astronomers can examine very early quasars that are ordinary, instead of seeing only the very brightest quasars.


• A massive, star-forming host galaxy: Follow-up on the galaxy hosting one of those ordinary quasars reveals a massive galaxy forming many stars – a new piece for the puzzle of galaxy formation.

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ESA’s space telescope Euclid has opened up a new chapter in the study of early galaxies. New research by Silvia Belladitta (Max Planck Institute for Astronomy, MPIA) and colleagues has followed up on one of the Euclid discoveries to uncover key properties of the host galaxy of one of the earliest supermassive black holes known in the universe.

Bright objects with a dark center

Active galactic nuclei known as quasars are responsible for some of the brightest celestial objects we see in the sky. The “engine” behind that enormous luminosity is matter falling onto a central supermassive black hole – a black hole with masses of millions, billions or an even greater number of solar masses. Such supermassive black holes are found in all but the smallest galaxies. Energy from the 'central engine' influences star formation in a galaxy (in particular the most massive galaxies): by either heating or compressing the gas that is the raw material for new stars, limiting star formation in the first case, enhancing it in the second.

How the first galaxies and their central black holes emerged is a highly active area of research. Finding the earliest quasars and examining their properties and the properties of their host galaxies is an important piece of the puzzle. But targeting the earliest quasars is challenging. Objects that we see as they were in the early universe are necessarily very far away. When light reaching our telescopes today shows us a quasar as it was 13.4 billion years ago, that is because the light needed 13.4 billion years to travel from its source to our telescopes.

Searching for “ordinary” quasars

At such great distances, even intrinsically bright objects like quasars appear rather dim. Easiest to observe are particularly bright specimens – but those, being exceptionally bright, are unlikely to be representative of their more normal siblings. When it comes to the population of quasars, we had so far seen only the tip of the iceberg. This is changing: Euclid’s combination of sensitivity and the ability to scan large areas of the sky at once makes it an ideal search machine for quasars in the early universe. Follow-up observations with ground-based telescopes confirm Euclid’s remarkable quasar-finding power.

Eduardo Bañados, group leader at MPIA and co-lead of the Euclid Quasar Work Package from 2022 to 2025, says: “Seeing Euclid deliver on its potential is immensely satisfying. But more than that, it marks a genuine shift: For the first time, we can study the typical early-universe quasar, not just exceptional outliers. We now have a real window onto how the bulk of the first black holes grew — and how they shaped the galaxies around them."

After only 1.5 years of data-taking, Euclid has more than doubled the number of known early quasars, from nine to 21 (“redshift z>7 quasars”, seen as they were less than 800 million years after the Big Bang). In fact, within a few months, Euclid broke the quasar redshift record not once, but twice!

Probing an extremely distant host galaxy

One refreshingly ordinary early quasar is the one that Belladitta and her team examined more closely. The quasar has the designation EUCL J125308.55+705432.3 (in the usual astronomy fashion, less a name than a detailed sky position). Light we receive today from this quasar was emitted 13 billion years ago, a mere 800 million years after the Big Bang (“z=7.7”). Its UV light amounts to only about 15% the brightness of previous redshift record-holding quasars.

For their follow-up, the astronomers used the NOEMA (NOrthern Extended Millimeter Array) observatory on the Plateau de Bure in the French Alps. NOEMA’s twelve 15-m-antennas act in concert like a single, much larger telescope. The astronomers observed submillimeter light at two carefully chosen wavelengths, each of which traces a different property of the quasar’s host galaxy.

Star formation and dust content

The first type of light is what astronomers call the [CII] line. This kind of light is produced in clouds of molecular gas where new stars are being born. The brightness of this line therefore indicates a galaxy’s star formation rate. The light also allows for a mass estimate: If you have ever heard the way that an emergency vehicle’s siren sound changes as the vehicle passes by, you know how motion influences the wavelength of waves. Applying the same principle in reverse, the way that the [CII] line is shaped allows astronomers to reconstruct the motion of gas in the quasar’s host galaxy, which in turn yields an estimate of its total mass.

The second type of light is thermal radiation from the cold dust in a galaxy. The intensity of this light reveals how much dust is present. The amount of dust is typically associated with the amount of molecular hydrogen, the raw material for star formation – of which this quasar appears to have a lot!

Reconstructing the galaxy’s star-formation rate

Taken together, Belladitta and her colleagues were able to reconstruct key properties of the galaxy that is hosting the quasar. The galaxy is forming stars at a rate of more than 250 solar masses per year – an impressive amount compared to the one solar mass per year of our own Milky Way, but not unexpected given previous finds for less distant quasars. The galaxy’s mass is estimated at around ten billion solar masses, a factor ten less than our own Milky Way. This is consistent with early galaxies that still have a lot of growth ahead of them.

"We found a galaxy that has all the ingredients to build a giant system: it is as massive as the hosts of the brightest early quasars and contains a huge reservoir of molecular gas to fuel intense star formation,” says Silvia Belladitta, a postdoctoral researcher at MPIA. Belladitta, who is the lead author of the study and the new co-leader of the Euclid Quasar Work Package, adds: “This raises an intriguing possibility. UV-faint quasars like EUCL J125308.55+705432.3 may be in a different evolutionary phase than their brighter cousins. Either the black hole is growing more slowly than in the brightest quasars, or else much of its activity is hidden behind thick clouds of dust. Distinguishing between these possibilities will be an exciting challenge for future observations.”

Future plans

For the big picture of galaxy evolution, these are incremental results. But they are pioneering achievements nonetheless, and they point the way forward: with the full 6-year Euclid survey expected to uncover hundreds of additional early quasars of this kind, and with follow-up observations like those of Belladitta and her colleagues providing an ever-larger set of information about star formation rates and galaxy masses, astronomy is steadily building a picture of the earliest galaxies and supermassive black holes in the universe. This will bring the story of the origin of galaxies, and of ourselves, into ever sharper focus.

Background information

The results described here have been published as Belladitta et al. “Euclid: A UV-faint quasar in a highly luminous star-forming host galaxy at z≈7.7” in the journal Astronomy & Astrophysics, doi: 10.1051/0004-6361/202659319. The Euclid quasar search results have been published as D. Yang et al., “Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8” in the journal Astronomy & Astrophysics, doi: 10.1051/0004-6361/202658883.

The MPIA scientists involved are Silvia Belladitta, Eduardo Banados, Fabian Walter, Knud Jahnke, Sarah Bosman, Julien Wolf, and Mischa Schirmer, in collaboration with Roberto Decarli (INAF Observatory, Bologna), Daming Yang (Leiden Observatory), Francesco Guarneri (University of Hamburg) and the rest of the EuclidCollaboration.

Euclid is ESA's mission to characterize Dark Energy and Dark Matter across cosmic time. Launched in 2023, Euclid will survey a third of the sky, recording images for two billion galaxies and precise distances of 50 million galaxies. Euclid's first major data release DR1 will provide data to the world for almost 2000 square degrees in November 2026. The Max-Planck-Institute for Astronomy (MPIA) is a founding member of the Euclid Consortium, a group of now more than 150 institutions across Europe, Canada, Japan, and the USA. During its construction MPIA has contributed hardware for the near-infrared instrument onboard Euclid. Now MPIA scientists are involved in its operation in orbit and are leading Euclid's overall calibration work.

Source: Max Planck Institute for Astronomy

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Contacts:

Dr. Markus Pössel
Head of press relations and outreach
Tel: +49 6221 528-261
Email: pr@mpia.de
Max Planck Institute for Astronomy, Heidelberg

Dr. Silvia Belladitta
Tel: +49 6221 528-102
Email: belladitta@mpia.de
Max Planck Institute for Astronomy, Heidelberg

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Original publication

Silvia Belladitta et al.
Euclid: A UV-faint quasar in a highly luminous star-forming host galaxy at z≈7.7
Astronomy & Astrophysics (2026)

DOI

Daming Yang (Leiden Observatory) et al.
Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8
Astronomy & Astrophysics (2026)

DOI

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From Dusk Till Dawn

Artist's impression of the exoplanet WASP-121 b. It belongs to the class of hot Jupiters. Due to its proximity to the central star, the planet's rotation is tidally locked to its orbit around it. As a result, one of WASP-121 b's hemispheres always faces the star, heating it to temperatures of up to 2500 degrees Celsius. The night side is always oriented towards cold space, which is why it is 1775 degrees Celsius cooler there. © Patricia Klein and MPIA

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To the point:

• Ultrahot exoplanet, atmospheric differences: Researchers discovered clear differences in the atmosphere between the morning and evening sides of the ultrahot gas planet WASP-121 b using the James Webb Space Telescope (JWST).


• Temperature and chemical variations: The evening side absorbs more infrared light due to higher temperatures caused by strong winds moving heat eastward, while water molecules decrease in the evening terminator due to high temperatures breaking them apart.


• Planetary rotation and observation method: WASP-121 b’s synchronous rotation reveals different atmospheric regions during transit, allowing scientists to analyse changes in light absorption over time and longitude.

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Astronomers find variations between the morning and the evening conditions of an ultra-hot exoplanet.

Astronomers have revealed distinct differences in atmospheric conditions between the morning and evening transition zones of the ultra-hot gas planet WASP-121 b, which separate day from night, commonly called terminators. This achievement was only possible due to the unmatched sensitivity of the James Webb Space Telescope (JWST). Led by Cyril Gapp, a PhD student at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, a team of researchers detected this phenomenon, which had previously been predicted by theoretical computations.

Confirmation of variations between dusk and dawn

The discovery corresponds to an asymmetry in the absorption of infrared light received from the host star, which is partially filtered through the planet’s atmosphere during its transit. The researchers interpret this as the result of non-uniform temperatures and chemical compositions in the exoplanet’s atmosphere.

With its unprecedented observational quality, JWST gives us the most detailed glimpses into distant planets to date: By measuring how star light absorption changes as WASP-121 b rotates, we probe its atmosphere longitude by longitude. Cyril Gapp, MPIA

The data indicate that the evening terminator absorbs more light than the morning side, consistent with the commonly accepted picture of powerful winds that transport intense heat from the day to the night side. Hot winds follow the planet’s rotation eastward, which heats the evening zone. With rising temperatures, this region is bound to expand, increasing the planet’s cross-section and allowing it to absorb stellar radiation more efficiently.

Besides a general slight reduction in brightness towards the end of the transit, the data obtained by JWST’s NIRSpec (Near-infrared spectrograph) instrument also reveal an increase in the carbon monoxide (CO) signal. However, this appears to be a temperature effect, not related to an increase in carbon monoxide molecules.

In contrast, the amount of water (H₂O) in the atmosphere appears to drop, which the astronomers interpret as a real decrease in water molecules. The temperatures in the upper atmosphere are high enough to break water molecules into their constituents. This result again corroborates the existence of hot winds heating the evening terminator region.

Top view of the orbit of the exoplanet WASP-121 b around its star. The planet’s rotation is synchronized to its orbit, both taking about 30 hours to complete. As a result, the planet constantly faces the star with the same side producing distinct day and night sides. The transition zones between those hemispheres are the morning and evening regions. Due to the planet’s proximity to the central star of only 1.9 stellar diameters, the planet rotates by about 30 degrees during its transit. © MPIA (CC BY 4.0)

Two extreme sides of an ultra-hot planet

To detect these minute variations, the astronomers exploited a peculiar behaviour of hot gas planets. The proximity to their host stars slowly synchronizes their spin and orbital motion via tidal forces,such that eventually one rotation takes as long as one revolution. Finally, these planets exhibit two distinct hemispheres: a hot side constantly facing the star and an opposite, darker and cooler side.

“WASP-121 b is particularly extreme, with average temperatures on the dayside hemisphere being around 2770 Kelvin, while those on the nightside are closer to about 1000 Kelvin,” co-author Tom Evans-Soma from the University of Newcastle, Australia, explains. He previously determined the planet’s temperature range and is also affiliated with MPIA. These values translate to almost 2500 degrees Celsius, or about 4525 degrees Fahrenheit, on the dayside, and approximately 725 degrees Celsius, or 1340 degrees Fahrenheit, at night.

When astronomers observe such a planet transiting in front of a star, the planet rotates slightly between the points of ingress and egress, revealing different fractions of its atmosphere. While the planet mostly presents its night side, our point of view permits glimpses beyond the dusk and dawn towards the bright dayside, depending on the transit’s progress. The zone leading the planet’s orbit corresponds to the morning side, and the one trailing is the evening side.

Apart from recording the measured brightness variation over time, spectrographs break light into smaller components, which physicists call a spectrum, much as a prism produces a rainbow-like distribution of colours. Since atmospheric gases absorb light at distinct colours or wavelengths, a detailed analysis reveals their chemical composition.

Elapsed time converts to longitude

Hence, the variation along the direction of rotation translates into a time-dependent change of the filtered signal. In the case of WASP-121 b the rotation angle during a full transit amounts to about 30 degrees, which is sufficient to probe the morning (dawn) and evening (dusk) terminators with high precision in longitude.

Astronomers usually average the measurements over the entire transit to achieve a clearer signal. However, to determine how the signal changes during the planet’s trajectory across the star, Gapp and his colleagues allowed for a temporal variation while the planet rotates. By applying statistical methods, they found that their procedure provides a significantly better fit to the data, indicating that they indeed detected a significant variation.

Notable gaps in atmospheric models

To verify the measured temperatures that would cause local expansion, the astronomers ran models simulating heat distribution in the upper layers of a gas planet, depending on the planet's properties and the constellation of the planet and its host star. While these atmospheric models confirmed the asymmetric effect caused by spatial temperature variations, the data revealed a larger signal amplitude than the models predicted.

The astronomers suspected that cooling mechanisms at the morning terminator might be at work that the models didn’t account for. Previous studies have indicated that clouds may be present, albeit composed not of water droplets but of minerals such as silicates. Clouds can efficiently shield infrared light emitted from hot gaseous layers below, mimicking lower temperatures. Infamously, simulating the physics of clouds, condensation, and evaporation in a dynamic environment is hard. Therefore, physical models commonly applied to exoplanet atmospheres, such as the one used in this study, do not account for clouds, which can yield unrealistic results.

After tweaking the simulation to better approximate the effect of clouds on infrared radiation from deeper layers, the results were more consistent with observations. However, only more sophisticated models will be able to confidently confirm the presence of clouds.

A blueprint for future studies

Model updates will also improve future investigations using this method. The astronomers have already identified additional suitable targets within the required temperature range and rotation speed to successfully probe the terminator regions. This will help them establish a sample of ultrahot gas planets, revealing their longitudinal structure, and potentially discover similarities and differences among these extreme worlds.

Additional information

MPIA astronomers involved in this study were Cyril Gapp (also Heidelberg University), Thomas M. Evans-Soma (also University of Newcastle, Australia), and Eva-Maria Ahrer.

Other researchers were: Aurélien Falco (Sorbonne Université, Paris, France), David K. Sing (Johns Hopkins University, Baltimore, USA), Shashank Dholakia (University of Queensland, St. Lucia, Australia), Vivien Parmentier (Université de la Côte d’Azur, Nice, France), Jérémy Leconte (Université Bordeaux, France), and Guangwei Fu (Johns Hopkins University).

The JWST observations used in this study were conducted as part of GO program #1729 (PI: Thomas Evans-Soma, Co-PI: Tiffany Kataria) titled “A NIRSpec Phase Curve for the ultrahot Jupiter WASP-121b” and GTO program #1201 (PI: David Lafreniere) labelled “NIRISS Exploration of the Atmospheric diversity of Transiting exoplanets (NEAT).”

NIRSpec (Near Infrared Spectrograph) was built by European industry to the European Space Agency’s (ESA) specifications and managed by the ESA JWST Project at ESTEC (European Space Research and Technology Centre), the Netherlands. The prime contractor was Airbus Defence and Space in Ottobrunn, Germany. MPIA contributed to the development and manufacture of NIRSpec’s filter and grating wheels. The NIRSpec detector and micro-shutter array subsystems were provided by NASA’s Goddard Space Flight Center (GSFC).

The James Webb Space Telescope is the world’s leading observatory for space research. It is an international programme led by NASA and its partners ESA and CSA (Canadian Space Agency).

Source: Max Planck Institute for Astronomy/Research Reports

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Contacs:

Dr. Markus Nielbock
Press and outreach officer
Tel: +49 6221 528-134
Email: pr@mpia.de
MPIA press team
Max Planck Institute for Astronomy, Heidelberg, Germany

Cyril Gapp
Tel: +49 6221 528-328
Email: gapp@mpia.de
Cyril Gapp / MPIA
Max Planck Institute for Astronomy, Heidelberg, Germany

Dr. Thomas M. Evans-Soma
Tel: +61 2 4055-3229
Email: tom.evans-soma@newcastle.edu.au
Homepage Thomas Evans-Soma
School of Information and Physical Sciences, The University of Newcastle, Callaghan, Australia
Max-Planck-Institut für Astronomie, Heidelberg, Deutschland

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Original publication

Cyril Gapp, Aurélien Falco, Thomas M. Evans-Soma, et al. (incl. Eva-Maria Ahrer)
Atmospheric asymmetries in WASP-121 b revealed by rotational transits detected with JWST
Nature Astronomy (2026). DOI: 10.1038/s41550-026-02887-6

Source

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Orbit of WASP-121 b around its host star (Video)

This animation illustrates the orbit of the exoplanet WASP-121 b around its host star, as well as its tidal locking. The perspective shifts from a top-down view of the orbit to the alignment during observation. During the transit, it becomes apparent that at the beginning and the end of the passage, a portion of the planet's illuminated dayside appears as a narrow crescent. T. Müller (MPIA/HdA)

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Downloads

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Astronomers Explore the Surface Composition of a Nearby Super-Earth

This high-resolution photo of the planet Mercury probably resembles the rocky exoplanet LHS 3844 b. Results from JWST observations favour an airless rocky planet with a dark, basalt-like surface, likely space-weathered by irradiation and meteorite impacts. © NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington (cropped)

Infrared spectrum of LHS 3844 b’s hot dayside derived from the brightness contrast to its host star in ppm (parts per million = 0.0001%) at different wavelengths. The observational data obtained from the James Webb and Spitzer Space Telescopes are consistent with mantle or lava rock, whereas they rule out an Earth-like crust. © Sebastian Zieba et al./MPIA

A close-up view of an astronaut’s boot print in the fine-powdered lunar regolith, during the Apollo 11 extravehicular activity (EVA) on the Moon. Similar conditions may exist on the exoplanet LHS 3844 b due to prolonged space weathering by stellar irradiation and meteorite impacts. © NASA

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To the point:

• JWST Observations: The James Webb Space Telescope analysed the rocky exoplanet LHS 3844 b, revealing a dark, hot surface without an atmosphere.


• Surface Composition: The analysis indicates the planet's surface is likely composed of basalt or mantle rock, ruling out a composition similar to Earth's silicate-rich crust.


• Geological Activity: The findings suggest that LHS 3844 b may have undergone prolonged geological inactivity, as no signs of volcanic gases were detected.

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Using MIRI (Mid Infrared Instrument) on board the James Webb Space Telescope (JWST), a team of researchers led by former MPIA (Max Planck Institute for Astronomy, Heidelberg, Germany) PhD student Sebastian Zieba (Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA) and Laura Kreidberg, MPIA Director and study PI (principal investigator), analysed the surface composition of the rocky exoplanet LHS 3844 b. Beyond characterizing exoplanetary atmospheres, this kind of deciphering the geological properties of planets orbiting distant stars is the next step in unveiling their nature. The results of this investigation are now published in the journal Nature Astronomy. A dark and airless rocky super-Earth

A dark and airless rocky super-Earth

LHS 3844 b is a rocky planet 30% bigger than Earth and orbits a cool red dwarf star once within roughly 11 hours. Whirling just three stellar diameters above the host star’s surface, the planet is tidally locked to its orbit. This means one rotation takes just as long as one revolution. As a result, the same hemisphere of LHS 3844 b always faces its star, producing a constant dayside with an average temperature of about 1000 Kelvin (approximately 725 Degrees Celsius or 1340 Degrees Fahrenheit). The LHS 3844 system is only 48.5 light-years (14.9 parsecs) away from Earth.

“Thanks to the amazing sensitivity of JWST, we can detect light coming directly from the surface of this distant rocky planet. We see a dark, hot, barren rock, devoid of any atmosphere. Laura Kreidberg, MPIA”

With its dark surface, LHS 3844 b may resemble a larger version of the Moon or the planet Mercury. This conclusion is based on analysing the infrared radiation received from the planet’s hot dayside. However, when measuring this radiation, we cannot see the planet directly; instead, we register the repeating change in brightness we receive from the star and the orbiting planet combined.

MIRI divided a portion of the planet’s infrared emission, ranging from 5 to 12 micrometres, into smaller wavelength sections and measured the brightness per wavelength bin. This is what astronomers call a spectrum, a rainbow-like distribution of the light’s components. Another data point, obtained from observations with the Spitzer Space Telescope and published a few years ago, augmented the analysis.

Constraining geological activity

Instead, the dark surface points to a composition reminiscent of terrestrial or lunar basalt, or of Earth’s mantle material. However, the astronomers attempted an even more detailed characterization.

A statistical analysis of how well this spectrum fits various mineral mixtures and configurations revealed that extended solid areas of basalt or magmatic rock best match the observations. They are rich in magnesium and iron and can include olivine. Crushed material, such as rocks or gravel, also fits fairly well, whereas grains or powders are inconsistent with the observations due to their brighter appearance, at least at first glance.

Without a protective atmosphere, planets are subjected to space weathering, predominantly driven by hard, energetic radiation from the host star and impacts from meteorites of various sizes.

“It turns out, these processes not only slowly dissolve hard rocks into regolith, a layer of fine grains or powder as found on the Moon,” explains Zieba. “They also darken the layer by adding iron and carbon, making the regolith’s properties more consistent with the observations.”

What can we deduce about an exoplanet's rocky surface?

Instead, the dark surface points to a composition reminiscent of terrestrial or lunar basalt, or of Earth’s mantle material. However, the astronomers attempted an even more detailed characterization.

A statistical analysis of how well this spectrum fits various mineral mixtures and configurations revealed that extended solid areas of basalt or magmatic rock best match the observations. They are rich in magnesium and iron and can include olivine. Crushed material, such as rocks or gravel, also fits fairly well, whereas grains or powders are inconsistent with the observations due to their brighter appearance, at least at first glance.

Without a protective atmosphere, planets are subjected to space weathering, predominantly driven by hard, energetic radiation from the host star and impacts from meteorites of various sizes.

“It turns out, these processes not only slowly dissolve hard rocks into regolith, a layer of fine grains or powder as found on the Moon,” explains Zieba. “They also darken the layer by adding iron and carbon, making the regolith’s properties more consistent with the observations.”

Geologically fresh or weathered? Two possible scenarios

This assessment left the astronomers with two scenarios for the planet’s surface that match the data equally well. One involves a surface dominated by dark, solid rock composed of basaltic or magmatic minerals. Compared to geological timescales, space weathering alters its properties quickly. Therefore, the astronomers conclude that, in this scenario, the surface should be relatively fresh, produced by recent geological activity, such as widespread volcanism.

The second scenario also proposes a dark surface, comparable to the Moon or Mercury. Still, it accounts for prolonged space weathering, which leads to extended regions covered by a darkened regolith layer, a fine powder also present on the Moon, as evidenced by the iconic photos of the astronauts’ footprints. This alternative relies on longer periods of geological inactivity, thereby requiring conditions opposite to the first scenario.

Attempts to resolve the ambiguity

These two alternatives differ in the degree of recent geological activity required. On Earth and other active objects in the Solar System, a typical phenomenon during such activity is outgassing. Sulphur dioxide (SO2) is a gas commonly connected to volcanism. If present on LHS 3844 b in reasonable amounts, MIRI should have detected it. Still, it found nothing. Therefore, a recent period of activity seems unlikely, which leads the astronomers to favour the second scenario. If correct, LHS 3844 b may truly look much like Mercury indeed.

In order to test their idea, Zieba, Kreidberg, and their colleagues are already pursuing a more direct approach. They have obtained additional JWST observations, which should enable them to discern surface conditions by exploiting small differences in how solid slabs and powders emit or reflect light. The distribution of emission angles depends on surface roughness, which affects the amount of radiation received at a given viewing angle. This concept is successfully applied to characterizing asteroids in the Solar System. “We are confident the same technique will allow us to clarify the nature of LHS 3844 b’s crust and, in the future, other rocky exoplanets,” concludes Kreidberg.

Additional information

Laura Kreidberg is the only MPIA astronomer involved in this study.

Other researchers were: Sebastian Zieba (Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA), Brandon P. Coy (Department of the Geophysical Sciences, University of Chicago, USA), Aaron Bello-Arufe (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA [JPL]), Kimberly Paragas (Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, USA), Xintong Lyu (Peking University, Beijing, China), Renyu Hu (The Pennsylvania State University, University Park, USA and JPL), Aishwarya Iyer (NASA Goddard Space Flight Center, Greenbelt, USA), Kay Wohlfarth (Technische Universität Dortmund, Germany)

The JWST observations used in this study were conducted as part of GO program #1846 (PI: Laura Kreidberg, co-PI: Renyu Hu) titled “A Search for Signatures of Volcanism and Geodynamics on the Hot Rocky Exoplanet LHS 3844 b.”

The MIRI consortium comprises the ESA (European Space Agency) member states: Belgium, Denmark, France, Germany, Ireland, the Netherlands, Spain, Sweden, Switzerland, and the United Kingdom. National science organisations fund the consortium’s work – in Germany, the Max Planck Society (MPG) and the German Aerospace Center (DLR). Participating German institutions include the Max Planck Institute for Astronomy in Heidelberg, the University of Cologne, and Hensoldt AG in Oberkochen, formerly Carl Zeiss Optronics.

The James Webb Space Telescope is the world’s leading observatory for space research. It is an international programme led by NASA and its partners ESA and CSA (Canadian Space Agency)..
The Spitzer Space Telescope was operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

Similar to how exoplanetary atmosphere research has benefited from climate science, this emerging field of exoplanetary geology draws on Earth-based geologic knowledge. Zieba, Kreidberg, and their collaborators ran models and accessed template libraries of rocks and minerals known from Earth, the Moon, and Mars to see what infrared signatures they would produce under the conditions on LHS 3844 b. Comparing observation-based data with these computations confidently ruled out a composition comparable to Earth’s crust, typically silicate-rich rocks such as granite.

Although this result is not very surprising – even in the Solar System, Earth is the only planet with such a crust – it may reveal details on LHS 3844 b’s geological history. Earth-like silicate-rich crusts are thought to form through a prolonged refinement process that requires tectonic activity and typically relies on water as a lubricant. The rocky material repeatedly melts and solidifies as it is mixed with mantle material, leaving the lighter minerals on the surface.

“Since LHS 3844 b lacks such a silicate crust, one may conclude that Earth-like plate tectonics does not apply to this planet, or it is ineffective,” says Sebastian Zieba. “This planet likely only contains little water.”

Source: Max Planck Institute for Astronomy/News

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Contacs:

Dr. Markus Nielbock
Press and outreach officer
Tel: +49 6221 528-134
Email: pr@mpia.de
MPIA press team
Max Planck Institute for Astronomy, Heidelberg, Germany

Prof. Dr. Laura Kreidberg
Director
Tel: +49 6221 528-215
Email: kreidberg@mpia.de
Laura Kreidberg / MPIA
Max Planck Institute for Astronomy, Heidelberg, Germany

Dr. Sebastian Zieba
NASA Sagan Fellow
Email: sebastian.zieba@cfa.harvard.edu
Sebastian Zieba / Harvard
Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA, USA

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Original publication

Sebastian Zieba, Laura Kreidberg, et al.
The dark and featureless surface of rocky exoplanet LHS 3844 b from JWST mid-infrared spectroscopy
Nature Astronomy (2026)

Source | DOI

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JWST/MIRI observing program information">JWST/MIRI observing program information

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Related Articles

From Heidelberg into outer space

December 20, 2021

The James Webb Space Telescope launches into space with equipment developed and built at the Max Planck Institute for Astronomy.

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Astronomers find an exo-Jupiter, and it seems to have clouds

Artist's impression of the planet Epsilon Indi Ab, with water clouds atop its ammonia-dominated atmosphere.
© E. C. Matthews, MPIA / T. Müller, HdA. Download image

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To the point

• New observations: Astronomers have used the James Webb Space Telescope to study the atmosphere of a massive Jupiter-analogue.


• Evidence for clouds: Surprisingly, the observations indicate the presence of water-ice clouds – previous models had been too simple!


• Part of a larger search: Observations and analysis provide a test run for certain challenges of observing a “second Earth”

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A team of astronomers led by Elisabeth Matthews at the Max Planck Institute for Astronomy (MPIA) has made a discovery that highlights the limits of most current models of exoplanet atmospheres: water-ice clouds on a distant Jupiter-like exoplanet called Epsilon Indi Ab. The way the observations were made has broader implications for exoplanet research: as an interesting immediate step on the path towards eventually finding and characterizing an Earth-analogue exoplanet.

Step by step towards a second Earth

Exoplanet research has an ambitious long-term goal: at some time within the next few decades, astronomers hope to be able to detect traces of life on an exoplanet. On the path towards that goal, exoplanet research has gone through several stages. In the first stage of research, from 1995 to about 2022, the main focus of exoplanet researchers was on detecting more and more exoplanets, using indirect methods that gave them information about the masses of some exoplanets, the diameters of others, and in some cases both mass and diameter.

When the James Webb Space Telescope (JWST) began operating in earnest in 2022, exoplanet research entered a second stage: High-quality, detailed information about the atmospheres of many exoplanets became available for a considerable number of planets, and researchers began to reconstruct the properties of such atmospheres in some detail. This is still at least one stage removed from realistic searches for life on exoplanets, which are expected to require the next generation of space telescopes.

With the new study, the astronomers are exploring some aspects of these next-level methods – although not yet for a planet like Earth. Elisabeth Matthews (Max Planck Institute for Astronomy), the study’s lead author, says: “JWST is finally allowing us to study solar-system analogue planets in detail. If we were aliens, several light years away, and looking back at the Sun, JWST is the first telescope that would allow us to study Jupiter in detail. For studying Earth in detail, we would need much more advanced telescopes, though.”

Elusive exo-Jupiters But as amazing as results from JWST about exoplanet atmospheres are, studying the analogues of our Solar System’s Jupiter has proven surprisingly difficult. Almost all gas giants studied with JWST so far differ from Jupiter in that they are much, much hotter – for the most common method of studying exoplanet atmospheres to work, the planet needs to pass in front of its host star from the perspective of an observer on Earth, and the probability for that configuration is much higher when the planet is closer to its star, which in turns makes the planet comparatively hot. The new study by Elisabeth Matthews and her colleagues uses a different technique. This is the closest observers have come to studying a Jupiter-analogue – and it has provided at least one surprise!

Matthews and her colleagues used JWST’s mid-infrared instrument MIRI to obtain direct images of the planet Epsilon Indi Ab. Naming conventions for exoplanets are such that this designation indicates the first planet discovered to orbit the star Epsilon Indi A in the constellation Indus (in the southern sky). Bhavesh Rajpoot, a PhD student at the Max Planck Institute for Astronomy who contributed to the study, says: “This planet has a considerably greater mass than Jupiter – the new study fixes its mass at 7.6 Jupiter masses – but the diameter is about the same as for its solar-system cousin.”

A more massive, slightly warmer Jupiter

Epsilon Indi Ab is about four times as distant from its central star as Jupiter is from the Sun. The star Epsilon Indi A itself is a bit less massive and a bit less hot than our Sun. This makes the surface temperature of Epsilon Indi Ab very low, at about 200 to 300 Kelvin (between –70 and +20 degrees Celsius). The reason the planet is slightly warmer than Jupiter (140 K) is that there is still a lot of heat remaining from the planet formation phase. Over the next billions of years, Epsilon Indi Ab will steadily cool down, eventually becoming colder than Jupiter. The astronomers used the coronagraph of the MIRI instrument to block out the central star’s light, which would otherwise outshine the planet’s much dimmer light. They then took an image through a very particular filter: 11.3 μm, which is just outside the wavelength region close to 10.6 μm that is characteristic for ammonia molecules NH3. The comparison with images at 10.6 μm that Matthews and her team had already taken in 2024 enabled the astronomers to estimate the amount of ammonia present. (Incidentally, both the mechanical filter wheels placing the coronagraph and the filter in front of the MIRI camera were constructed at MPIA, one of the German contributions to the JWST.)

Surprising evidence for clouds

For Jupiter, both ammonia gas and ammonia clouds dominate the upper layers of the atmosphere that are visible in observations. Given its properties, Epsilon Indi Ab was thought to have massive amounts of ammonia gas as well, although not ammonia clouds. Surprisingly, the photometric comparison showed somewhat less ammonia than expected. The best explanation Matthews and her colleagues found for this deficit was the presence of thick but patchy water-ice clouds, similar to the high-altitude cirrus clouds in Earth’s atmosphere – an unexpected complication!

In interpreting observations of this kind, astronomers compare their data to simulations of planetary atmospheres. But most of the published models neglect to include clouds, as the presence of clouds makes the computation that much more complicated – clearly something theorists will need to fix! James Mang (University of Texas at Austin), a co-author of the study, says: “It’s a great problem to have, and it speaks to the immense progress we’re making thanks to JWST. What once seemed impossible to detect is now within reach, allowing us to probe the structure of these atmospheres, including the presence of clouds. This reveals new layers of complexity that our models are now beginning to capture, and opens the door to even more detailed characterization of these cold, distant worlds.”

An opportunity for the Roman Space Telescope

On the upside, there is an upcoming opportunity for observing the water-ice clouds, which are very reflective directly: NASA’s Nancy Grace Roman Space Telescope, where MPIA is a partner, is slated for launch in 2026–2027, and should be suitable for exactly that kind of observation. In the meantime, Matthews and her colleagues are applying for JWST observation time to target additional cold Jupiter-analogues. And at the same time that Matthews and other astronomers are learning more about cold exo-Jupiters, their observational techniques are laying the groundwork that, if all goes well, will help future observers target earthlike planets, in search of life.

Background information

The results described here have been published as E. C. Matthews et al., “A second visit to Eps Ind Ab with JWST: new photometry confirms ammonia and suggests thick clouds in the exoplanet atmosphere of the closest super-Jupiter” in the Astrophysical Journal Letters.

The MPIA researchers involved are Elisabeth Matthews and Bhavesh Rajpoot, in collaboration with James Mang and Caroline Morley (University of Texas at Austin), Aarynn Carter and Mathilde Mâlin (Space Telescope Science Institute), and others.

Source: Max Planck Institute for Astronomy/News

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Contacts:

Dr. Markus Pössel
Head of press relations and outreach
Tel: +49 6221 528-261
pr@mpia.de
Max Planck Institute for Astronomy, Heidelberg

Dr. Elisabeth Matthews
Tel: +49 6221 528-102
matthews@mpia.de
Max Planck Institute for Astronomy, Heidelberg

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Original publication

Elisabeth C. Matthews, James Mang, Aarynn L. Carter, Mathlide Mâlin, Caroline V. Morley, Bhavesh Rajpoot, Leindert A. Boogaard, Jennifer A. Burt, Ian J. M. Crossfield, Fabo Feng, Anne-Marie Lagrange, Mark W Phillips
A second visit to Eps Ind Ab with JWST: new photometry confirms ammonia and suggests thick clouds in the exoplanet atmosphere of the closest super-Jupiter

Astrophysical Journal Letters (2026)

Source | DOI

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SPHERE’s debris disk gallery: tell-tale signs of dust and small bodies in distant solar systems

SPHERE gallery of debris disks, visible by the starlight they reflect, with the central star blocked out.
© N. Engler et al./SPHERE Consortium/ESO

Images of dust around distant exoplanets provide a glimpse of asteroids and comets in other solar systems

To the point:

• Traces of comets and asteroids in distant solar systems: In young planetary systems, mutual collisions between asteroids or comets generate large amounts of dust, forming a "debris disk". The disk contains information about the system’s smaller bodies.


• Observational challenge accepted: Producing debris disk images is difficult, in particular because of the glare of the bright star in the center. The SPHERE instrument was optimised for that kind of observation.


• Familiar structures: Some of the disks imaged with SPHERE show structures reminiscent of the solar system, with asteroids concentrated in an asteroid belt inside the giant planet orbits, comets in a “Kuiper belt” outside.

Observations with the instrument SPHERE at ESO’s Very Large Telescope have produced an unprecedented gallery of “debris disks” in exoplanetary systems. Gaël Chauvin (Max Planck Institute for Astronomy), project scientist of SPHERE and co-author on the paper publishing the results, says: “This data set is an astronomical treasure. It provides exceptional insights into the properties of debris disks, and allows for deductions of smaller bodies like asteroids and comets in these systems, which are impossible to observe directly.”

In our own solar system, once you look beyond the Sun, the planets, and dwarf planets like Pluto, there is a bewildering array of smaller (“minor”) bodies. Of particular interest are the larger small bodies, with diameters between about a kilometer and several hundred kilometers. We call those objects comets if they put on (at least occasionally) a display of losing gas and dust to form distinctive visible structures like a tail, and asteroids when they don’t. Small bodies provide a glimpse of the earliest history of the solar system: In the evolution from dust grains to full-size planets, small bodies called planetesimals are a transitional stage, and the asteroids and comets are remnants from that stage – planetesimals that did not manage to evolve into larger planets. Small bodies are (somewhat) modified remnants of the building material for planets like our Earth!

Small bodies around stars other than the Sun?

So far, astronomers have detected more than 6000 exoplanets (that is, planets orbiting stars other than the Sun), giving us a much better idea of the diversity of planets out there, and of the place of our solar system within this teeming population. Taking actual images of such planets is a considerable challenge, though. At this time, there are less than 100 exoplanets that astronomers have been able to image, and even giant planets are no more than a structureless little blob on such images. “Finding any direct clues about the small bodies in a distant planetary system from images seems downright impossible. The other indirect methods used to detect exoplanets are no help, either” says Dr Julien Milli, astronomer at the University Grenoble Alpes and co-author of the study.

The solution, ironically, comes from stuff that is even smaller, by orders of magnitude. In particular in younger planetary systems, planetesimals will regularly collide – sometimes to stick together to form a larger body, sometimes to go their separate ways. These collisions create copious amounts of new dust, and the dust, it turns out, can be observed over large distances, given suitable instruments: Whenever you divide an object into smaller components, the total volume remains the same, but the total surface area increases. Divide an asteroid with a diameter of one kilometer into dust grains with diameters of one micrometer (= millionth of a meter), and you increase the overall surface by a factor of a billion! That is, in large part, why it is possible to observe debris disks around young stars by the starlight they reflect. Observe the dust, and you can glean information about the planetary system’s small bodies.

These images of the debris disks around the star HD 106906 (left) and that around HR 4796 (right) showcase the amount of detail that is possible with SPHERE. © N. Engler et al./SPHERE Consortium/ESO

Observing debris disks

Over time, such a debris disk will fade. Collisions will become less frequent. Dust will be blown out of the system by radiation pressure, caught by planetesimals or planets, or ends up in the central star. Our own solar system provides an example of what is left after billions of years: In this case, there are two remaining planetesimal belts, namely the asteroid belt between Mars and Jupiter, and a reservoir of comets outside the orbits of the giant planets in what is known as the Kuiper belt. There is also dust in our solar system’s main orbital light, known as zodiacal dust. Under a very dark sky, you will be able to see light reflected by that dust with the naked eye shortly after sunset or shortly before sunset, the so-called zodiacal light.

This configuration would be difficult to detect for alien astronomers studying our solar system from afar. But as the present study has shown, with the best current telescopes and instruments, for not-too-far-away systems, the dust should be observable for about the first 50 million years of the debris disk’s life. Which is not to say that such observations are not a considerable technical challenge! Imaging a debris disk is like taking a picture of a puff of cigarette smoke, but the smoke is hovering next to a bright stadium floodlight, and you are trying to take the picture from a distance of several kilometers. This is where suitable instrumentation makes all the difference, and it is where the SPHERE instrument, which began operating at one of ESO’s Very Large Telescopes (VLT) in the spring of 2014, excels.

Blocking out starlight

At the heart of SPHERE is a very simple concept. If in everyday life, we want to look at something and the Sun in the background is making this difficult, we put up a hand to block out the sunlight. When SPHERE observes an exoplanet or debris disk, it uses a coronagraph to block out the star’s light – in effect, a little disk inserted in the optical pathway that removes most of the starlight before the image is taken. The catch is that unless imaging is very precise and stable, this simple recipe cannot work in practice!

To meet the stringent requirements, SPHERE utilizes an extreme version of adaptive optics, where the unavoidable perturbations caused by the light passing through Earth’s atmosphere are analyzed and largely compensated for in real time through the use of a deformable mirror. Another, optional part of SPHERE filters out light with specific properties (“polarised light”) that are characteristic for light reflected by something like dust particles, as opposed to starlight, setting the stage for particularly sensitive debris disk images.

An unprecedented gallery of debris disk images

The new publication presents an unprecedented collection of debris disk images, produced with SPHERE from starlight reflected by small dust particles in these systems. "To obtain this collection, we processed data from observations of 161 nearby young stars whose infrared emission strongly indicates the presence of a debris disk," says Natalia Engler (ETH Zurich), the lead author of the study. "The resulting images show 51 debris disks with a variety of properties — some smaller, some larger, some seen from the side and some nearly face-on – and a considerable diversity of disk structures. Four of the disks had never been imaged before."

Comparisons within a larger sample are crucial for discovering the systematics behind object properties. In this case, an analysis of the 51 debris disks and their stars confirmed several systematic trends: When a young star is more massive, its debris disk tends to have more mass as well. The same is true for debris disks where the majority of the material is located at a greater distance from the central star.

Finding asteroid belts and Kuiper belts in other systems

Arguably the most interesting feature of the SPHERE debris disks are the structures within the disks themselves. In many of the images, disks have a concentric ring- or band-like structure, with disk material predominantly found at specific distances from the central star. The distribution of small bodies in our own solar system has a similar structure, with small bodies concentrated in the asteroid belt (asteroids) and the Kuiper belt (comets).

All of these belt structures appear to be associated with the presence of planets, specifically of giant planets, clearing their neighbourhoods of smaller bodies. Some of the giant planets had been observed already. In some of the SPHERE images, features like sharp inner edges or disk asymmetries give tantalizing hints of as-yet unobserved planets. In this way, the SPHERE disk collection sets interesting targets for future observations: the JWST, or the Extremely Large Telescope (ELT) currently under construction by ESO should allow astronomers to produce images of the planets that create these structures.

Background information

The results described here have been published as Natalia Engler et al., “Characterization of debris disks observed with SPHERE,” in the journal Astronomy and Astrophysics. DOI: 10.1051/0004-6361/202554953

The MPIA researchers involved are Gaël Chauvin, Thomas Henning, Samantha Brown, Matthias Samland, and Markus Feldt, in collaboration with Natalia Engler (ETH Zürich), Julien Milli (CNRS, IPAG, Université Grenoble Alpes), Nicole Pawellek (University of Vienna), Johan Olofsson (ESO), Anne-Lise Maire (CNRS, IPAG, Université Grenoble Alpes), and others

Source: Max Planck Institute for Astronomy/Research Reports

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Contacts:

Dr. Markus Pössel
Head of press relations and outreach
Tel: +49 6221 528-261
pr@mpia.de
Max Planck Institute for Astronomy, Heidelberg

Dr. Gaël Chauvin
Tel: +49 6221 528-287
chauvin@mpia.de
Max Planck Institute for Astronomy, Heidelberg

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Original publication

N. Engler, J. Milli, N. Pawellek, R. Gratton, P. Thébault, C. Lazzoni, J. Olofsson, H.M. Schmid, S. Ulmer-Moll, C. Perrot, J.-C. Augereau, S. Desidera, G. Chauvin, et al.
Characterization of debris disks observed with SPHERE
Astronomy and Astrophysics

DOI

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“Black Hole Stars” could solve JWST riddle of overly massive early galaxies

Artist’s impression of a black hole star (not to scale). The cut-out reveals the central black hole with it surrounding accretion disk. What makes this a black hole star is the surrounding envelope of turbulent gas. This configuration can explain what astronomers observe in the object they are calling “The Cliff.” © MPIA/HdA/T. Müller/A. de Graaff

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A newly discovered distant object that astronomers have dubbed “The Cliff” could solve a riddle posed by some of the first observations of the distant universe with the James Webb Space Telescope, related to the discovery of a population of objects dubbed “little red dots.” Those objects were thought to be young galaxies, but with such considerable mass as would have been difficult to explain in current models of cosmic evolution. “The Cliff” has led to a proposal that could resolve this problem: Little red dots are not galaxies, but instead supermassive black holes that are embedded in a thick envelope of gas. The researchers call this new class of object a “black hole star.”

n the summer of 2022, less than a full month after the James Webb Space Telescope (JWST) had begun to produce its first scientific images, astronomers noticed something unexpected: little red dots. In pictures taken at JWST’s unprecedented sensitivity, these extremely compact, very red celestial objects showed very clearly in the sky, and there appeared to be a considerable number of them. JWST had apparently discovered a whole new population of astronomical objects, which had eluded the Hubble Space Telescope. That latter part is unsurprising. “Very red” is astronomy lingo for objects that emit light predominantly at longer wavelengths. The little red dots emit light predominantly at wavelengths beyond a 10 millionth of a meter, in the mid-infrared. Hubble cannot observe at wavelengths this long. JWST, on the other hand, is designed to cover this range.

Additional data showed that these objects were far away indeed. Even the closest examples were so far away that their light had taken 12 billion years to reach us. Astronomers always look into the past, and we see an object whose light takes 12 billion years to reach us as it was those 12 billion years ago, a mere 1.8 billion years after the Big Bang.

Unexplainable young, massive galaxies?

This is where things get dicey. In order to interpret astronomical observations, you need a model of the object in question. When astronomers point to their data and say, “This is a star,” the statement comes with a lot of baggage. It is trustworthy only because astronomers have robust physical models of what a star is – in short, a giant plasma ball held together by its own gravity, producing energy by nuclear fusion in its centre. You also need a good understanding of how stars look, both in images and in the rainbow-like decomposition of light known as a spectrum. In turn, if you see an object with the right kind of appearance and the right kind of spectrum, you can confidently state that it is a star.

The little red dots did not seem to fit into any of the usual slots, so astronomers set out to look beyond the standard objects. One of the first interpretations offered was a bombshell in and of itself: In this interpretation, little red dots were galaxies that were extremely rich in stars, their light reddened by huge amounts of surrounding dust. Within our own cosmic neighborhood, if you put our solar system in a cube one light-year a side, that cube would only contain a single star: our Sun. In the star-rich galaxies postulated to explain little red dots, a cube that size would contain several hundred thousand stars.

In our home galaxy, the Milky Way, the only region that dense in stars is the central nucleus, but that contains only about one thousandth of the stars needed in those little-red-dot models. The sheer number of stars involved, as high as hundreds of billions of solar masses’ worth less than a billion years after the Big Bang, raised major questions about astronomers’ basic understanding of galaxy evolution: Could we even explain how these galaxies produced so many stars, so quickly? Co-author Bingjie Wang (Penn State University) explains: “The night sky of such a galaxy would be dazzlingly bright. If this interpretation holds, it implies that stars formed through extraordinary processes which have never been observed before.”

Galaxies vs. active galactic nuclei

The interpretation itself remained controversial. The community split into two camps: One group that favored the many-stars-plus-dust interpretation, and another that interpreted little red dots as active galactic nuclei, but also obscured by copious dust. Active galactic nuclei are what we see when a steady stream of matter falls onto a galaxy’s central black hole, forming an exceedingly hot, so-called accretion disk around the central object. But this second interpretation came with its own set of limitations. There are marked differences between the spectra of little red dots and those of the dust-reddened active galactic nuclei astronomers had previously observed. In addition, this interpretation would require extremely large masses for the supermassive black holes at the center of those objects – and surprisingly many of those, given the large number of little red dots that had been found.

There was a consensus, too: that in order to resolve the puzzle, astronomers would need more and different observational data. The original JWST observations had provided images. For testing physical interpretations, astronomers need spectra: detailed information about how much light an object emits at different wavelengths. For the top telescopes, there is considerable competition for observing time. Once it became clear just how interesting little red dots were, numerous astronomers world-wide began to apply for time to observe them more closely. One such application was the RUBIES program formulated by Anna de Graaff at the Max Planck Institute for Astronomy in Heidelberg and an international team of colleagues, where the acronym stands for “Red Unknowns: Bright Infrared Extragalactic Survey.”

The distant treasures of RUBIES

The RUBIES application was successful, and between January and December 2024, the astronomers used nearly 60 hours of JWST time to obtain spectra from a total of 4500 distant galaxies, one of the largest spectroscopic data sets obtained with JWST to date. As Raphael Hviding (MPIA) says: “In that data set, we found 35 little red dots. Most of them had already been found using publicly available JWST images. But the ones that were new turned out to be the most extreme and fascinating objects.” Most interesting of all was the spectrum for an object the astronomers found in July 2024. The astronomers dubbed the object in question “The Cliff,” and it seemed to be an extreme version of the population of little red dots – and by that very fact a promising test case for interpretations of just what little red dots were. The Cliff is so distant from us that its light took 11.9 billion years to reach us (redshift z=3.55).

A curious similarity to single stars

With this unmissable, unusual feature, The Cliff looked like it did not fit any of the interpretations that had been proposed for little red dots. But De Graaff and her colleagues wanted to make sure. They constructed diverse variations of all the models that tried to cast little red dots either as massive star-forming galaxies or as dust-shrouded active galactic nuclei, attempted to reproduce the spectrum of The Cliff with each one, and failed every single time.

Anna de Graaff says: “The extreme properties of The Cliff forced us to go back to the drawing board, and come up with entirely new models.“ By that time, the idea that Balmer-break features in a spectrum might be due to something other than stars had entered the discussion (in the shape of a September 2024 article by two researchers based in China and the UK). De Graaff and her colleagues had started to wonder about something very similar themselves: Balmer breaks can be found both in the spectra of single, very hot, young stars and in the spectra of galaxies containing a sufficient number of such very hot, young stars. Weirdly, The Cliff looked more like the spectrum of a single star than that of a whole galaxy.

Enter black hole stars

On this basis, de Graaff and her colleagues developed a model some of them have taken to calling a “black hole star,” written as BH*: An active galactic nucleus, that is, a supermassive black hole with an accretion disk, but surrounded and reddened not by dust, but by virtue of being embedded in a thick envelope of hydrogen gas. The BH* is not a star in the strict sense, since there is no nuclear fusion reactor in its center. In addition, the gas in the envelope is swirling much more violently (there is much stronger turbulence) than in any ordinary stellar atmosphere. But the basic physics is similar: The active galactic nucleus heats the surrounding gas envelope, just like the nuclear-fusion-driven center of a star heats the star’s outer layers, so the external appearance has marked similarities.

The models formulated by de Graaff and colleagues at this point are proofs-of-concept – pioneering work, but not by any measure a perfect fit. Still, these black hole star models describe the data much better than any other type of model. In particular, the shape of the name-giving cliff in the spectrum is nicely explained by assuming a turbulent, dense, spherical gas envelope around an AGN. From that perspective, The Cliff would be an extreme example where the central black hole star dominates the object’s brightness. For the other little red dots, their light would be a more even mixture of the central black hole star with the light from stars and gas in the surrounding parts of the galaxy.

A new mechanism for rapid early galaxy formation?

If a black hole star is indeed the solution, it might have another potential advantage. Systems of this kind had previously been studied in a purely theoretical setting, with much lighter intermediate-mass black holes. There, the setup with central black hole and surrounding gas envelope was seen as a way for the mass of a very early galaxies’ central black holes growing particularly quickly. Given that JWST has found solid evidence for high-mass black holes in the early universe, a configuration that could explain ultra-fast mass growth of black holes would be a welcome addition to current galaxy evolution models. Whether the supermassive black hole stars can do the same is still undetermined, but it would be an intriguing expansion of their role if they did!

As promising as this sounds, caveats are in order. The new result is brand-new. Reporting on it conforms with accepted practice of covering scientific results once they are published in, or at least accepted by, a peer-reviewed journal. But in order to know whether this becomes a trusted part of astronomy’s view of the universe, we will need to wait at least a few more years.

Open questions

The present result does represent a major step forward: the first model that can explain the unusual shape of The Cliff, the extreme object’s Balmer break. Like any significant step forward, it leads to new, open research questions: How could such a black hole star have formed? How can the unusual gas envelope be sustained over a longer time? (Since the black hole gobbles up surrounding gas, there needs to be a mechanism for “refueling” the envelope.) How do the other features of the spectrum of The Cliff come about?

Answering those questions requires contributions from astrophysical modeling, but it is also set to benefit from further in-depth observation. In fact, de Graaff and her team already have the approval of JWST follow-up observations for little red dots of particular interest, such as The Cliff, scheduled for next year.

These future observations will shed light on whether black hole stars are indeed the explanation for how today’s galaxies came to be what they are. At this point in time, that outcome is an intriguing possibility, but far from certain.

Background information

The results described here have been accepted for publication as A. de Graaff et al., “A remarkable Ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a Little Red Dot at z = 3.5” in the journal Astronomy & Astrophysics. The paper led by Raphael Hviding that presents the full sample of Little Red Dots in the RUBIES data set has been accepted for publication in the same journal.

The MPIA researchers involved are Anna de Graaff, Hans-Walter Rix and Raphael E. Hviding, in collaboration with Gabe Brammer (Cosmic Dawn Center), Jenny Greene (Princeton University), Ivo Labbe (Swinburne University), Rohan Naidu (MIT), Bingjie Wang (Penn State University and Princeton University), and others.

“The Cliff” gets its name from the most prominent feature of its spectrum: a steep rise in what would be the ultraviolet region, at wavelengths just a little shorter than that of violet visible light. “Would” because our universe is expanding: A direct consequence is that, for an object as distant as The Cliff, that wavelength is stretched to almost five times its original value, landing squarely in the near-infrared (“cosmological redshift”). A prominent rise of this kind, at these wavelengths, is known as a “Balmer break.” Balmer breaks can be found in the spectra of ordinary galaxies, where they are usually seen in galaxies that form little to no new stars at the time. But in those cases, the rise is much less steep than The Cliff.

Source: Max Planck Institute for Astronomy/New

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Contacts:

Dr. Markus Pössel
Head of press relations and outreach
Tel: +49 6221 528-261
pr@mpia.de
Max Planck Institute for Astronomy, Heidelberg

Dr. Anna De Graaff
Tel:+49 6221 528-367
degraaff@mpia.de
Max Planck Institute for Astronomy, Heidelberg

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Original publication

Anna de Graaff, Hans-Walter Rix, Rohan P. Naidu, et al.
A remarkable ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a little red dot at z = 3.5
Astronomy & Astrophysics, 701, A168 (2025)

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