How does matter accrete from the molecular cloud onto the central star?
Matter accretion is a fundamental process in the formation of stars. To understand this process better, a team of researchers conducted a survey called PROSAC (PROtostellar Submillimeter Array Survey) using the Submillimeter Array. They focused on studying low-mass protostars in their early evolution, from the Class 0 stage to the Class I stage.
During the formation of a star, matter needs to move from the large-scale molecular cloud through the circumstellar disk and finally onto the central star. This process of matter accretion determines the growth and evolution of the protostar.
By studying 20 Class 0 and I protostars, the researchers aimed to unravel the mechanisms driving the accretion process. To achieve this, they employed detailed dust radiative transfer models, which allowed them to disentangle the continuum emission from the envelopes and disks surrounding the protostars.
What is the framework used to estimate the masses of the envelopes and disks?
The researchers developed a framework using radiative transfer models to estimate the masses of the envelopes and disks surrounding the protostars. This framework considered the continuum emission observed at (sub)millimeter wavelengths and employed sophisticated modeling techniques.
Using this approach, they were able to separate the emission coming from the envelopes and disks, enabling them to estimate their individual masses. By analyzing the HCO+ 3-2 line emission from the Class I sources, they could further refine their estimations.
Is there a correlation between disk mass and evolutionary stage?
The researchers discovered an intriguing contrast when analyzing the correlation between disk mass and evolutionary stage. While no evidence for a correlation was found between disk mass and the evolutionary stage of young stellar objects, there was a clear correlation when considering the envelope mass.
Although the disks surrounding both Class 0 and I protostars had typical masses of around 0.05 Msun, the envelope mass drastically decreased as the protostellar evolution progressed. In the Class 0 stage, the envelope mass was approximately 1 Msun, while in the Class I stage, it dropped to below 0.1 Msun.
This unexpected finding highlights the unique nature of disk evolution during the early stages of star formation. Further research is needed to fully understand the mechanisms driving these differences between disk and envelope masses.
How do the central star masses relate to the total mass in the star-disk-envelope system?
The distribution of mass within the star-disk-envelope system is vital to understanding the dynamics of protostellar evolution. The researchers found that, for the Class I sources where Keplerian rotation was observed, the central stars contained a significant portion of the system’s total mass.
In fact, these late-stage Class I sources showed that the central stars contained between 70% and 98% of the total mass in the star-disk-envelope system. This finding confirms that these objects are in advanced stages of their embedded protostellar evolution.
Do theoretical models accurately estimate disk masses in the late Class I stage?
The researchers compared their observational results with theoretical models and found some discrepancies regarding disk masses in the late Class I stage. Theoretical models tended to overestimate the disk masses relative to the stellar masses in this stage of protostellar evolution.
This discrepancy points to the complexity of disk evolution and the need to refine theoretical models to better predict disk masses during the later stages of star formation. Understanding these discrepancies is crucial for advancing our knowledge of protostellar evolution and the physical processes that govern it.
When are circumstellar disks formed?
One important outcome of this study is the support it provides for the early formation of circumstellar disks during protostellar evolution. The researchers found strong evidence that circumstellar disks are formed early on and rapidly process material accreted from the larger-scale envelope onto the central star.
This finding challenges previous assumptions that disks form at a later stage in the evolution of protostars. Instead, it suggests that disks play a significant role in shaping the evolution of low-mass protostars from the Class 0 to the Class I stage.
Implications of the Research:
The PROSAC survey and its findings contribute significantly to our understanding of the accretion process and protostellar evolution. The key implications of this research are:
- This study sheds light on the mechanisms by which matter is accreted from molecular clouds onto central stars, providing insights into the overall star formation process.
- The framework developed for estimating envelope and disk masses can be applied to future studies, enabling a better understanding of the mass distribution within protostellar systems.
- Understanding the correlation (or lack thereof) between disk mass and evolutionary stage helps refine theories about the formation and evolution of circumstellar disks.
- The relationship between central star masses and the total mass in the star-disk-envelope system provides valuable information about the maturity of protostars and their evolutionary stages.
- The discrepancy between observed disk masses and theoretical predictions highlights the need for further research and refinement of models to improve our understanding of disk evolution.
- The evidence supporting early formation of circumstellar disks challenges existing theories and enhances our knowledge of protostellar evolution.
Overall, the PROSAC survey provides invaluable insights into the formation and evolution of low-mass protostars, advancing our knowledge of star formation and contributing to the broader field of astrophysics.
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Source: https://arxiv.org/abs/0909.3386
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