SPACE/COSMOS
ALMA measures evolution of monster barred spiral galaxy
National Institutes of Natural Sciences
image:
Left: The galaxy J0107a observed in infrared light with the James Webb Space Telescope. The two galaxies seen in the lower part of the image are unrelated foreground objects. (Credit: NASA) Right: The gas distribution in J0107a observed with ALMA. The large amounts of gas visible on the leading edges of the bar are being channeled towards the galactic center. (ALMA(ESO/NAOJ/NRAO), Huang et al.)
view moreCredit: NASA / ALMA(ESO/NAOJ/NRAO)
Astronomers have observed a massive and extremely active barred spiral galaxy in the early Universe and found that it has important similarities and differences with modern galaxies. This improves our understanding of how barred spiral galaxies, like our own Milky Way Galaxy, grow and evolve.
Some spiral galaxies, including the Milky Way, exhibit a straight bar inside the spiral pattern. This bar structure helps channel gas towards the center of the galaxy where it can be used to form new stars. But why bars form in only about half of spiral galaxies, and how they influence the evolution of the galaxy are unanswered questions.
To study the evolution of spiral galaxies in the early Universe, researchers led by Shuo Huang, a project researcher at the National Astronomical Observatory of Japan and Nagoya University, used the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope to observe a massive barred spiral galaxy known as J0107a that existed 11.1 billion years ago. Located in the constellation Cetus, J0107a is a “monster” galaxy, meaning a galaxy growing rapidly in the early Universe by forming many new stars. Because they are located far away, it has been difficult to see the detailed structure of monster galaxies and determine what is driving this vigorous star formation. Recently the improved resolution provided by the James Webb Space Telescope has revealed spirals and even bars in some of the monster galaxies. J0107a is the earliest and most massive barred spiral galaxy known to date, so it is the best target for studying the evolution of barred spiral galaxies in the early Universe.
The team found that in J0107a the distribution and motion of gas in the bar is similar to modern galaxies. But compared to modern galaxies, the concentrations of gas are several times higher and the speed of the gas flow is faster, reaching several hundred kilometers per second. Astronomers believe that this massive influx of gas to the center will fuel signification additional star formation, helping to drive the evolution of this monster galaxy. This is the first time these features have been observed, and they were not predicted by theoretical or simulation models.
Huang comments, “We expect that the detailed information about the distribution and movement of gas gained through these observations will provide important clues for exploring not only the origins of the diversity of galaxies, but also the formation and evolution of more normal barred spiral galaxies.”
Journal
Nature
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Large gas inflow driven by a matured galactic bar in the early Universe
Article Publication Date
21-May-2025
Titan's Moon mysterious wobbling atmosphere like gyroscope, new research suggests
University of Bristol
image:
Purple haze around Titan – A false-colour image of Titan captured in 2004 by the Cassini spacecraft. The purple haze shows the dense atmosphere enveloping the moon’s golden body.
view moreCredit: NASA/JPL/Space Science Institute. Terms of Use: https://www.esa.int/ESA_Multimedia/Terms_and_conditions_of_use_of_images_and_videos_available_on_the_esa_website
The puzzling behaviour of Titan’s atmosphere has been revealed by researchers at the University of Bristol for the first time.
By analysing data from the Cassini-Huygens mission, a joint venture between NASA, the European Space Agency (ESA), and the Italian Space Agency, the team have shown that the thick, hazy atmosphere of Saturn’s largest moon doesn’t spin in line with its surface, but instead wobbles like a gyroscope, shifting with the seasons.
Titan is the only moon in the Solar System with a significant atmosphere, and one that has long captivated planetary scientists. Now, after 13 years of thermal infrared observations from Cassini, researchers have tracked how Titan’s atmosphere tilts and shifts over time.
“The behaviour of Titan’s atmospheric tilt is very strange!” said Lucy Wright, lead author and postdoctoral researcher at Bristol’s School of Earth Sciences. “Titan’s atmosphere appears to be acting like a gyroscope, stabilising itself in space.
“We think some event in the past may have knocked the atmosphere off its spin axis, causing it to wobble.
“Even more intriguingly, we’ve found that the size of this tilt changes with Titan’s seasons.”
The team studied the symmetry of Titan’s atmospheric temperature field and found that it isn’t centred exactly on the pole, as expected. Instead, it shifts over time, in step with Titan’s long seasonal cycle—each year on Titan lasts nearly 30 years on Earth.
Professor Nick Teanby, co-author and planetary scientist at Bristol said: “What’s puzzling is how the tilt direction remains fixed in space, rather than being influenced by the Sun or Saturn.
“That would’ve given us clues to the cause. Instead, we’ve got a new mystery on our hands.”
This discovery will impact NASA’s upcoming Dragonfly mission, a drone-like rotorcraft scheduled to arrive at Titan in the 2030s. As Dragonfly descends through the atmosphere, it will be carried by Titan’s fast-moving winds—winds that are about 20 times faster than the rotation of the surface.
Understanding how the atmosphere wobbles with the seasons is crucial for calculating the landing trajectory of Dragonfly. The tilt affects how the payload will be carried through the air, so this research can help engineers better predict where it will touch down.
Dr Conor Nixon, planetary scientist at NASA Goddard and co-author of the study, added: “Our work shows that there are still remarkable discoveries to be made in Cassini’s archive.
“This instrument, partly built in the UK, journeyed across the Solar System and continues to give us valuable scientific returns.
“The fact that Titan’s atmosphere behaves like a spinning top disconnected from its surface raises fascinating questions—not just for Titan, but for understanding atmospheric physics more broadly, including on Earth.”
The team’s findings contribute to a growing body of research suggesting Titan is not just Earth-like in appearance but an alien world with climate systems all its own, and many secrets still hidden beneath its golden haze.
Paper:
‘Seasonal Evolution of Titan’s Stratospheric Tilt and Temperature Field at High-Resolution from Cassini/CIRS’ by Lucy Wright et al in the Planetary Science Journal (PSJ).
NASA’s Dragonfly mission rotorcraft.
Credit
NASA/Johns Hopkins APL/Steve Gribben
The wobble of Titan’s atmosphere. The atmosphere is tilted relative to Titan’s solid body, and this tilt varies in size and direction
Credit
Titan image credit: NASA/JPL/Space Science Institute Diagram by Lucy Wright
Journal
Planetary Science
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
‘Seasonal Evolution of Titan’s Stratospheric Tilt and Temperature Field at High-Resolution from Cassini/CIRS’
Article Publication Date
22-May-2025
Dwarf galaxy clustering challenges standard cold dark matter paradigm
Chinese Academy of Sciences Headquarters
A new study of diffuse dwarf galaxies is challenging the prevailing galaxy formation model within the standard Cold Dark Matter (CDM) framework, leading to a proposed new model of dark matter.
Under the direction of Prof. WANG Huiyuan from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences, the research team identified for the first time an exceptionally strong clustering pattern in diffuse dwarf galaxies.
The study was published in Nature.
Dwarf galaxies, like all galaxies, sit within a halo of dark matter. These halos formed early in the universe and shaped where galaxies could form.
Nevertheless, not all dark matter halos are the same. Some are more likely to be found in denser regions of the universe than others. This is called "halo bias" and comes in two types—"mass bias," which holds that massive halos cluster more strongly, and "assembly bias," which holds that among halos of the same mass, those with different halo properties exhibit different clustering. For example, the halos formed earlier (old halos) cluster more strongly than those formed later (young halos).
Historically, massive galaxies were the primary focus for detecting halo assembly bias, due to their higher luminosity and more efficient observability by surveys such as the Sloan Digital Sky Survey (SDSS). In contrast, dwarf galaxies have often been underrepresented in such studies because of their low luminosity and the challenges associated with sparse sampling.
However, the USTC researchers have revealed that dark matter halos hosting dwarf galaxies also exhibit halo bias, which is largely unaffected by uncertainties in halo mass estimations. This finding suggests that halo assembly bias may be more effectively traced through dwarf galaxies compared to their more massive counterparts.
In this study, Prof. WANG's team analyzed a sample of isolated dwarf galaxies from the SDSS, revealing that diffuse dwarf galaxies—whose stars are farther apart—display unexpectedly strong large-scale clustering compared to compact dwarf galaxies—whose stars are closer together. This unexpected finding fundamentally contradicts the established understanding of galaxy clustering derived from studies of massive galaxies.
Through their proprietary Exploring the Local Universe with reConstructed Initial Density field (ELUCID) cosmological simulation, the researchers found that this “inverted” phenomenon was intrinsically linked to the formation time of halos. Specifically, the spatial distribution of diffuse dwarf galaxies closely aligned with old halos, while compact dwarf galaxies followed patterns similar to young halos. This represents the first high-confidence observational evidence for halo assembly bias based on real-world data, bridging the gap between cosmological simulations and empirical validation.
However, existing galaxy formation models under the standard CDM paradigm fail to explain the formation of diffuse dwarf galaxies in old halos, implying potential contradictions between current galaxy formation models and dark matter models, on the one hand, and the actual Universe, on the other. To overcome this contradiction, the researchers introduced the Self-Interacting Dark Matter (SIDM) model.
This model posits that dark matter particles interact not only via gravity, but also via weak non-gravitational interactions. These interactions cause structural expansion and weaken the central gravitational strength in old halos, thereby promoting the formation of diffuse dwarf galaxies. Conversely, young halos exhibit weaker such effects, favoring the formation of compact dwarf galaxies. This theory well explains the observed correlation between halo age and galaxy density, suggesting that the nature of dark matter may be more complex than previously thought.
Reviewers from Nature highly commended this work: "This is an original and very surprising (and thus significant) result. Testing predictions of dark matter self-interactions through galaxy clustering is a novel approach and could have a lasting impact."
This work represents the first observational confirmation of significant halo assembly bias—a breakthrough that defines critical parameters for modeling the nature of dark matter, the evolution of cosmic large-scale structures, and the mechanisms governing galaxy formation and evolution. It reveals a unique correlation between the structures of baryonic components and the ages of their host halos in dwarf galaxies, fundamentally challenging the standard CDM paradigm and necessitating potential modifications.
Journal
Nature
Article Title
Unexpected clustering pattern in dwarf galaxies challenges formation models
Article Publication Date
21-May-2025
Astronomers find protoplanetary disk candidates in galactic center
image:
Sky models and simulated observations by ALMA
view moreCredit: XU Fengwei; ALMA Partnership; and Laura Pérez of NRAO
Are we alone in the Universe? And where did our planetary home come from? For decades, astronomers have attempted to answer these question by studying planetary formation. In the process, they have discovered hundreds of protoplanetary disks—structures around young stars that resemble what our own solar system likely looked like in its earliest stage.
Most protoplanetary disks have been observed in cosmically quiet environments. However, in a breakthrough that could reshape our understanding of how planetary systems form, an international team of astronomers has uncovered over 500 dense star-forming cores—many likely harboring protoplanetary disks—within three representative molecular clouds in the Milky Way's Central Molecular Zone (CMZ)—a high-pressure, high-density region near the Milky Way Galactic Center.
The study, conducted by researchers from the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences (CAS), Kavli Institute for Astronomy and Astrophysics at Peking University (KIAA, PKU), and the University of Cologne (UoC), provides rare insight into how stars and planets may emerge under extreme galactic conditions.
Detecting such systems in the CMZ is exceptionally challenging. These regions are distant, faint, and deeply embedded in thick layers of interstellar dust. To overcome these obstacles, the researchers utilized the Atacama Large Millimeter/submillimeter Array (ALMA), an interferometric telescope that combines signals from antennas spread over several kilometers to achieve extraordinary angular resolution. This allows astronomers to peer through thick layers of interstellar dust and resolve features as small as 1,000 astronomical units (AU) at distances of 8.3 kiloparsecs—equivalent to about 17 billion AU.
To maximize detail, the team employed dual-band observations, capturing data at two different wavelengths simultaneously. This technique offers critical spectral information about temperature, dust composition, and structural characteristics—much like how human vision uses color contrast to make sense of the world. Dual-band imaging provides critical spectral information about the temperature, dust properties, and structure of these remote systems.
"Only with ALMA can we open this sharp new window onto one of the most enigmatic regions of our Galaxy," said Prof. LU Xing, a researcher at SHAO and the Principal Investigator of the ALMA observational project.
Among the most striking findings: over 70% of the dense cores exhibited unexpected spectral reddening. After eliminating possible observational artifacts, the researchers proposed two main interpretations, both implying the widespread presence of protoplanetary disks—structures thought to represent early stages of solar system formation.
"We were astonished to see these 'little red dots' cross the whole molecular clouds," said XU Fengwei, first author of the study and now a PhD student at KIAA, PKU and exchange student at UoC. "They are telling us the hidden nature of dense star-forming cores."
One explanation is that these cores are not transparent, homogeneous spheres, as once thought. Instead, they may contain smaller, optically thick structures—possibly protoplanetary disks—whose self-absorption at shorter wavelengths results in the observed reddening.
"This challenges our original assumption of canonical dense cores," said Prof. WANG Ke, XU's supervisor.
Alternatively, the reddening could result from grain growth within the cores.
"In typical interstellar environments, dust grains are only a few microns in size," said Prof. Hauyu Baobab Liu, who led the radiative transfer modeling in the study. "But our models indicate that some cores may contain millimeter-sized grains, which could only form in protoplanetary disks and then be expelled—perhaps by protostellar outflows."
Regardless of which scenario prevails, both require the presence of protoplanetary disks. The findings suggest that over 300 such systems may already be forming within just these three CMZ clouds.
Future multi-band observations will help to further constrain their physical properties and evolutionary stages—offering a rare glimpse into the early processes that give rise to planetary systems like our own, even in the most extreme corners of the Milky Way.
This work was supported by the National Key R&D Program of China, the Strategic Priority Research Program of CAS, and the National Natural Science Foundation of China, among others.
Journal
Astronomy and Astrophysics
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Dual-band Unified Exploration of three CMZ Clouds (DUET) Cloud-wide census of continuum sources showing low spectral indices
