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"Molecular clouds"
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FEEDBACK: a SOFIA Legacy Program to Study Stellar Feedback in Regions of Massive Star Formation
FEEDBACK is a SOFIA (Stratospheric Observatory for Infrared Astronomy) legacy program dedicated to study the interaction of massive stars with their environment. It performs a survey of 11 galactic high mass star-forming regions in the 158 m (1.9 THz) line of [C ii] and the 63 m (4.7 THz) line of [O i]. We employ the 14 pixel Low Frequency Array and 7 pixel High Frequency Array upGREAT heterodyne instrument to spectrally resolve (0.24 MHz) these far-infrared fine structure lines. With a total observing time of 96h, we will cover ∼6700 arcmin2 at 14 1) angular resolution for the [C ii] line and 6 3 for the [O i] line. The observations started in spring 2019 (Cycle 7). Our aim is to understand the dynamics in regions dominated by different feedback processes from massive stars such as stellar winds, thermal expansion, and radiation pressure, and to quantify the mechanical energy injection and radiative heating efficiency. This is an important science topic because feedback of massive stars on their environment regulates the physical conditions and sets the emission characteristics in the interstellar medium (ISM), influences the star formation activity through molecular cloud dissolution and compression processes, and drives the evolution of the ISM in galaxies. The [C ii] line provides the kinematics of the gas and is one of the dominant cooling lines of gas for low to moderate densities and UV fields. The [O i] line traces warm and high-density gas, excited in photodissociations regions with a strong UV field or by shocks. The source sample spans a broad range in stellar characteristics from single OB stars, to small groups of O stars, to rich young stellar clusters, to ministarburst complexes. It contains well-known targets such as Aquila, the Cygnus X region, M16, M17, NGC7538, NGC6334, Vela, and W43 as well as a selection of H ii region bubbles, namely RCW49, RCW79, and RCW120. These [C ii] maps, together with the less explored [O i] 63 m line, provide an outstanding database for the community. They will be made publically available and will trigger further studies and follow-up observations.
Journal Article
Magnetic Fields in the Formation of Sun-Like Stars
We report high-angular-resolution measurements of polarized dust emission toward the low-mass protostellar system NGC 1333 IRAS 4A. We show that in this system the observed magnetic field morphology is in agreement with the standard theoretical models of the formation of Sun-like stars in magnetized molecular clouds at scales of a few hundred astronomical units; gravity has overcome magnetic support, and the magnetic field traces a clear hourglass shape. The magnetic field is substantially more important than turbulence in the evolution of the system, and the initial misalignment of the magnetic and spin axes may have been important in the formation of the binary system.
Journal Article
The alignment of molecular cloud magnetic fields with the spiral arms in M33
Magnetic component in star formation
Many mechanisms have been proposed to explain galactic star formation, thought to occur mainly in interstellar molecular clouds that are rich in dust and gas. Some cloud-formation models suggest that a large-scale galactic magnetic field is irrelevant at the scale of individual clouds; others say that galactic fields are strong enough to impose their direction on individual clouds. Using the Submillimeter Array at Mauna Kea in Hawaii, Hua-bai Li and Thomas Henning have observed magnetic fields from the M33 galaxy in the constellation Triangulum, our nearest face-on galaxy with pronounced optical spiral arms. They find six giant molecular cloud complexes, all aligned with the spiral arms, suggesting that the large-scale field in M33 anchors the clouds.
The formation of molecular clouds, which serve as stellar nurseries in galaxies, is poorly understood. A class of cloud formation models suggests that a large-scale galactic magnetic field is irrelevant at the scale of individual clouds, because the turbulence and rotation of a cloud may randomize the orientation of its magnetic field
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,
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. Alternatively, galactic fields could be strong enough to impose their direction upon individual clouds
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,
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, thereby regulating cloud accumulation and fragmentation
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, and affecting the rate and efficiency of star formation
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. Our location in the disk of the Galaxy makes an assessment of the situation difficult. Here we report observations of the magnetic field orientation of six giant molecular cloud complexes in the nearby, almost face-on, galaxy M33. The fields are aligned with the spiral arms, suggesting that the large-scale field in M33 anchors the clouds.
Journal Article
Unveiling Extensive Clouds of Dark Gas in the Solar Neighborhood
From the comparison of interstellar gas tracers in the solar neighborhood (HI and CO lines from the atomic and molecular gas, dust thermal emission, and g rays from cosmic-ray interactions with gas), we unveil vast clouds of cold dust and dark gas, invisible in HI and CO but detected in [gamma] rays. They surround all the nearby CO clouds and bridge the dense cores to broader atomic clouds, thus providing a key link in the evolution of interstellar clouds. The relation between the masses in the molecular, dark, and atomic phases in the local clouds implies a dark gas mass in the Milky Way comparable to the molecular one.
Journal Article
Fractional stars
This study examines the possibility of starting the process of collapsing and forming stars from a fractional molecular cloud. Although the Verlinde’s approach is employed to derive the corresponding gravitational potential, the results are easily generalizable to other gravitational potential proposals for fractional systems. It is due to the fact that the different methods, despite the difference in the details of results, all obtain power forms for the potential in terms of radius. An essential result of this analysis is the derivation of the corresponding Jeans mass limit, which is a crucial parameter in understanding the formation of stars. The study shows that the Jeans mass of a cloud in fractional gravity is much smaller than the traditional value. In addition, the study also determines the burning temperature of the resulting star using the Gamow theory. This calculation provides insight into the complex processes that govern the evolution of these celestial bodies. Finally, the study briefly discusses the investigation of hydrostatic equilibrium, a crucial condition that ensures the stability of these fractional stars. It also addresses the corresponding Lane–Emden equation, which is pivotal in understanding this equilibrium.
Journal Article
Magnetogravitational instability in strongly coupled rotating clumpy molecular clouds including heating and cooling functions
Molecular cloud (MC) formation is caused by the gravitational collapse mechanism and is significantly affected by radiative heating and cooling processes. This paper analyzes the gravitational instability in strongly coupled clumpy molecular clouds (MCs), under the effects of uniform rotation, magnetic field, and heat-loss functions. The generalized hydrodynamic equations coupled with the modified energy equation (which incorporates the heating and cooling effects due to cloud-cloud collisions) are used to describe the mathematical model. Following Jeans stability analysis, it is found that the value of the critical Jeans wavenumber decreases due to the strong coupling between the plasma particles (coupling parameter) and clump stirring processes (heating rate), so both have a stabilizing influence on the onset of gravitational collapse in clumpy MCs. The influence of various parameters on the growth rate of the instability is discussed numerically, and it is found that the cooling rate parameter that describes cloud-cloud collisions shows a destabilizing effect. The region of instability is observed to be smaller in the strongly coupled clumps (kinetic limit) than in the weakly coupled (hydrodynamic limit) clumps. The results are helpful in understanding the role of heating and cooling mechanisms in the MC formation.
Journal Article
Million-Degree Plasma Pervading the Extended Orion Nebula
Most stars form as members of large associations within dense, very cold (10 to 100 kelvin) molecular clouds. The nearby giant molecular cloud in Orion hosts several thousand stars of ages less than a few million years, many of which are located in or around the famous Orion Nebula, a prominent gas structure illuminated and ionized by a small group of massive stars (the Trapezium). We present x-ray observations obtained with the X-ray Multi-Mirror satellite XMM-Newton, revealing that a hot plasma with a temperature of 1.7 to 2.1 million kelvin pervades the southwest extension of the nebula. The plasma flows into the adjacent interstellar medium. This x-ray outflow phenomenon must be widespread throughout our Galaxy.
Journal Article
Possibilities for Methanogenic and Acetogenic Life in Molecular Clouds
According to panspermia, life on Earth may have originated from life forms transported through space from elsewhere. These life forms could have passed through molecular clouds, where the process of methanogenesis could have provided enough energy to sustain living organisms. In this study, we calculate the Gibbs free energy released from synthesizing hydrocarbons for methanogenic (acetogenic) life in a molecular cloud, with methane (acetic acid) as the final metabolic product. Our calculations demonstrate that the chemical reactions during methanogenesis can release enough free energy to support living organisms. The methanogenic life may have served as the predecessor of life on Earth, and there is some preliminary evidence from various molecular biology studies to support this idea. Furthermore, we propose a potential distinguishing signal to test our model.
Journal Article
Waves on the surface of the Orion molecular cloud
Orion nebula making waves
The molecular cloud in the Orion nebula, at about 414 parsecs from Earth, gives us our closest view of massive-star formation. It has been predicted from star-formation models that the gases heated and ionized in the process will generate wave-like structures as they are blown over pre-existing molecular gas. These waves have now been observed, in a new series of radio maps of the Orion nebula. The waves are thought to result from Kelvin–Helmholtz instability, a phenomenon seen at the interface between fluids with different densities and velocities, and further observations of such periodic structures should provide insight into the mechanisms of massive-star formation and its effects on the surrounding region of the molecular cloud.
It has long been suspected that the development of hydrodynamical instabilities can compress or fragment a molecular cloud (in which stars are born). One key signature of an instability would be a wave-like structure in the gas, although this has not yet been seen. Now, the presence of 'waves' is reported at the surface of the Orion cloud, near where massive stars are forming. The waves probably arise as gas that is heated and ionized by massive stars is blown over pre-existing molecular gas.
Massive stars influence their parental molecular cloud, and it has long been suspected that the development of hydrodynamical instabilities can compress or fragment the cloud
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,
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. Identifying such instabilities has proved difficult. It has been suggested that elongated structures (such as the ‘pillars of creation’
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) and other shapes arise because of instabilities
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,
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, but alternative explanations are available
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,
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. One key signature of an instability is a wave-like structure in the gas, which has hitherto not been seen. Here we report the presence of ‘waves’ at the surface of the Orion molecular cloud near where massive stars are forming. The waves seem to be a Kelvin–Helmholtz instability that arises during the expansion of the nebula as gas heated and ionized by massive stars is blown over pre-existing molecular gas.
Journal Article