Massive stars, defined as those exceeding eight solar masses, play a crucial role in the cosmos. They influence cosmic evolution through their powerful radiation, stellar winds, and explosive deaths as supernovae, which dramatically alter the surrounding interstellar environment. Unlike their low-mass counterparts, which often form through straightforward gravitational collapse, the origins of massive stars are labyrinthine, taking place in highly dynamic and large-scale gas environments. Prior to this research, the step-by-step transport of gas into these structures to form accretion disks remained elusive, leaving researchers with questions about the underlying mechanisms.

Utilizing the renowned Atacama Large Millimeter/submillimeter Array (ALMA) in conjunction with maser astrometry—a technique that employs microwaves to pinpoint gas positions—scientists meticulously traced the gas accretion process in a specific massive star-forming region. Amplifying their observational capabilities, the researchers incorporated data from the Very Large Array (VLA), an advanced radio telescope located in New Mexico, USA.

The scope of their research spanned distances from approximately 2,500 astronomical units (AU) down to 40 AU from the protostar, illustrating how gas moves closer to the center of star formation. This is particularly significant because one astronomical unit is equivalent to the mean distance from the Earth to the Sun. Their findings, published on September 17, were lauded for providing a “textbook case” that elucidates the hierarchical structures and gas accretion processes unique to massive star formation.

The observations focused on the massive star-forming region known as IRAS 18134-1942, which is situated about 1.25 kiloparsecs from the Sun. The researchers unveiled a striking, layered architecture of gas flows that mirrored complex cosmic structures. At the broadest scale, they identified numerous spiral-like streams that guide gas inwardly, sculpted by the parent cloud’s rotation and collapse. As these streams converge, they form a distinct, elongated bar-like structure funneling gas further towards the center. As one approaches the protostar, the gas transforms into a rotating envelope, and as this evolution culminates within a few hundred AU, an accretion disk presenting Keplerian rotation emerges.

The revelations of this study highlight an unexpected efficiency in the transport of gas. Research indicated that the inflow rate maintained a steady average of roughly one ten-thousandth of a solar mass per year within the spiral and bar structures. However, this rate dwindled to about one millionth of a solar mass per year at the scale of the disk. Consequently, this suggests a regulatory function among the envelope and disk, fundamentally influencing the growth efficiency of protostars.

Moreover, researchers identified an intriguing misalignment in the rotation axis of the envelope compared to the protostellar disk. This misalignment, while not a direct reversal, points toward the influence of turbulent inflows imparting uneven angular momentum during the accretion process. The findings challenge previous assumptions about the chaotic nature of gas dynamics in these environments, revealing that the internal structures of massive molecular clouds exhibit highly organized, galaxy-like hierarchical patterns.

Dr. MAI Xiaofeng, a prominent astronomer from SHAO and the study’s first and corresponding author, emphasized the significance of these results. He remarked that the findings provide pivotal observational evidence regarding how massive stars gather mass and form their accretion disks in complex environments. This evidence challenges long-standing views and opens avenues for fresh exploration in the study of stellar formation.

The effort is part of the ambitious international ALMA-ATOMS/QUARKS survey, which has been diligently accruing multiscale data from over 140 massive star-forming regions over the last five years. This expansive database enhances the understanding of star formation processes across different cosmic settings.

Building upon this foundational research, Dr. LIU Tie, the project leader and co-corresponding author, expressed the team’s ambition to study additional systems utilizing ALMA and ongoing follow-up observations, in tandem with advanced numerical simulations. This integrated approach aims to further unveil the comprehensive dynamics involved in massive star creation, culminating in a broader understanding of stellar evolution.

Through this pioneering work, researchers at SHAO have set the stage for a new chapter in astrophysical research, illuminating the complexities of massive star formation. As the team continues to investigate the intricate web of gas dynamics, they hope to unveil even more insights that can revolutionize the field of astrophysics and deepen our comprehension of the universe’s fundamental processes.

This research not only contributes essential knowledge to the field but also raises intriguing questions about the interplay between massive stars and the broader cosmic environment, prompting further inquiry into the fundamental mechanisms that govern the lifecycle of stars and galaxies.

Subject of Research: Gas accretion processes in massive star formation
Article Title: A misaligned protostellar disk fed by gas streamers in a barred spiral-like massive dense core
News Publication Date: 17-Sep-2025
Web References: DOI
References: N/A
Image Credits: Credit: SHAO

Keywords

Massive stars, star formation, gas accretion, accretion disks, ALMA, VLA, hierarchical structures, astrophysics, cosmic evolution.

The phenomenon of binary star systems is well-known, but the intricate processes leading to the formation of such remarkable pairs can be extraordinarily complex. In a binary system, two stars orbit a common center of mass, and various factors—including mass transfer and gravitational interactions—play pivotal roles in shaping their evolutionary path. What sets the system containing PSR J1928+1815 apart is the specific formation mechanism theorized to have established this unique binary configuration.

Central to the understanding of this new binary system is the concept of common envelope evolution. During this process, one stellar companion expands and engulfs its partner, resulting in the formation of a shared envelope. Over time, this common envelope can lead to dramatic outcomes, particularly when one of the stars is a neutron star. The neutron star’s intense gravitational field allows it to draw matter from its companion star, triggering the common envelope phase. As mass is exchanged, the companion star’s outer layers are expelled, ultimately leaving behind a remarkable binary system comprising a recycled neutron star and a stripped-down helium star.

The recent study led by ZongLin Yang and his colleagues meticulously characterized the binary system PSR J1928+1815. Their findings unveiled that the pulsar is locked in a close orbit with the helium star, completing a full revolution every 3.6 hours. This tight orbital configuration indicates a remarkably intimate relationship between the two stars, raising intriguing questions about the forces at play in their ongoing evolutionary saga. The pulsar’s rapid rotation rate—indicative of its millisecond classification—can be attributed to the mass it siphoned from its companion during the common envelope phase.

The authors utilized sophisticated stellar models to elucidate the process that led to the formation of PSR J1928+1815. They postulated that an unstable mass transfer event from the helium star to the neutron star initiated a series of rapid interactions, resulting in the ejection of the companion star’s outer envelope. This complex interaction allowed the neutron star to spiral inward, inching closer to the core of the helium star, thereby releasing an extraordinary amount of energy. The outcome of this interaction was the stabilization of the remaining binary system, a feat not previously documented in any observable binary systems.

The discovery of PSR J1928+1815 has profound implications on our understanding of the evolution of binary star systems, particularly those that involve compact objects like neutron stars. Researchers estimate that there could be as many as 84 undiscovered binary systems of this nature residing within our Milky Way galaxy. These predictions highlight both the rarity and the significance of the newly identified system, emphasizing the need for continued exploration and observation of stellar phenomena in the universe.

Despite the novelty of this discovery, the authors acknowledge that much about these systems remains shrouded in mystery. The common envelope evolution process is not yet fully caught in the spotlight of scientific understanding, as researchers continue to unravel the multitude of factors that impact stellar evolution. Further investigations into the dynamics of PSR J1928+1815 and similar systems will be essential for fleshing out our theoretical frameworks and refining the models that govern such extraordinary stellar interactions.

The implications of this research extend beyond the confines of astrophysics, shedding light on the nature of gravitational interactions, the life cycles of stars, and the intricate relationships that govern stellar evolution. As researchers delve deeper into the mechanics of such unique arrangements, we are presented with an opportunity to expand our knowledge of the cosmos and its ceaseless wonders.

In addition to PSR J1928+1815, the study opens avenues for future investigations into similar binary systems. Armed with enhanced observational capabilities and refined theoretical models, scientists are poised to seek out additional examples hiding within the vast expanse of our galaxy. This ongoing quest will not only enrich our understanding of binary star systems but will also contribute to broader astronomical discoveries.

The technology deployed in the characterization of PSR J1928+1815 plays a crucial role in the advancement of astrophysical research. Employing the Five-hundred-meter Aperture Spherical radio Telescope, a marvel of engineering and design, astronomers have gained unprecedented access to the invisible radio wave emissions of pulsars. The data retrieved from such instruments is invaluable, unlocking insights about the behavior and properties of these compact celestial entities.

In conclusion, the discovery of the binary system PSR J1928+1815 marks a pivotal moment in the study of millisecond pulsars and their evolution. Through continued research and exploration, we are reminded of the complexities and wonders of the universe, where every new finding paves the way for deeper inquiries. As astronomers push the boundaries of our understanding, the cosmos continues to unfold its secrets, revealing the intricate tapestry that characterizes our existence.

Subject of Research: Binary Star Systems
Article Title: A pulsar-helium star compact binary system formed by common envelope evolution
News Publication Date: 22-May-2025
Web References: DOI link here
References: Articles on binary star evolution and pulsar studies.
Image Credits: Provided by the American Association for the Advancement of Science (AAAS).

Keywords

Binary star systems, millisecond pulsars, helium stars, common envelope evolution, neutron stars, astronomical observations, cosmic evolution, stellar interactions.