Nonhomologous contraction and equilibria of self-gravitating, magnetic interstellar clouds embedded in an intercloud medium: Star formation. II - Results

1976 ◽  
Vol 207 ◽  
pp. 141 ◽  
Author(s):  
T. C. Mouschovias
Keyword(s):  
Star Formation ◽  
Interstellar Clouds ◽  
Intercloud Medium

scholarly journals Abundances in Diffuse Interstellar Clouds

1980 ◽  
Vol 5 ◽  
pp. 293-300 ◽  
Author(s):  
M. Jura
Keyword(s):  
Interstellar Extinction ◽  
Future Research ◽  
Chemical Compositions ◽  
Interstellar Clouds ◽  
Dark Clouds ◽  
Neutral Gas ◽  
Self Gravity ◽  
Ultraviolet Observations ◽  
Diffuse Clouds ◽  
Intercloud Medium

Interstellar clouds are concentrations of cold (T ≲ 100 K) neutral gas (cf. Spitzer 1978) which are immersed within an intercloud medium. It is worthwhile to distinguish between diffuse clouds (roughly those with E[B-V] ≳ 0.5) and dark clouds (those with E[B-V] ≳ 0.5). This distinction is useful in the sense that diffuse clouds are relatively warm (T ∼ 100 K), they are composed mostly of atomic species except for hydrogen which can be appreciably molecular, and they are dynamically controlled by their interaction with the intercloud medium. Dark clouds are relatively cold (T ∼ 10 K), they contain a rich variety of molecules, and self-gravity is important in their evolution. Because the interstellar extinction is a rapid function of wavelength, most ultraviolet observations have been of diffuse clouds. The IUE satellite is sufficiently powerful that observations of some dark clouds are possible, and an important area of future research will be to delineate more quantitatively the similarities and differences between diffuse clouds and dark clouds.With ultraviolet observations, considerable progress has been made in understanding the physical characteristics of clouds including determinations of their densities, temperatures, chemical compositions and dynamics (cf. Spitzer and Jenkins 1976). Because particular progress has been made on understanding the abundances within diffuse clouds and because of the limitations of space, we restrict this review to a discussion of abundances within diffuse clouds. These abundance measurements provide a set of fundamental astrophysical data.

scholarly journals The Gas-to-Dust Ratio in the Galaxy

1974 ◽  
Vol 60 ◽  
pp. 179-182
Author(s):  
F. J. Kerr ◽  
G. R. Knapp
Keyword(s):  
Globular Clusters ◽  
Galactic Latitude ◽  
Interstellar Clouds ◽  
The Galaxy ◽  
Intercloud Medium

We have investigated the gas-to-dust ratio in the Galaxy by comparing 21-cm Hicolumn densities with the color excesses of globular clusters. We find a constant gas-to-reddening ratio in interstellar clouds and the intercloud medium. This ratio is also independent of galactic latitude.

scholarly journals Starbursts Triggered by Cloud Compression in Interacting Galaxies

1999 ◽  
Vol 186 ◽  
pp. 235-242
Author(s):  
Chanda J. Jog
Keyword(s):  
High Pressure ◽  
Star Formation ◽  
Shock Compression ◽  
Physical Mechanism ◽  
Hydrogen Gas ◽  
Interacting Galaxies ◽  
Giant Molecular Clouds ◽  
Main Mode ◽  
Radiative Shock ◽  
Intercloud Medium

We propose a physical mechanism for the triggering of starbursts in interacting spiral galaxies by shock compression of the pre-existing disk giant molecular clouds (GMCs). We show that as a disk GMC tumbles into the central region of a galaxy following a galactic tidal encounter, it undergoes a radiative shock compression by the pre-existing high pressure of the central molecular intercloud medium. The shocked outer shell of a GMC becomes gravitationally unstable, which results in a burst of star formation in the initially stable GMC. In the case of colliding galaxies with physical overlap such as Arp 244, the cloud compression is shown to occur due to the hot, high-pressure remnant gas resulting from the collisions of atomic hydrogen gas clouds from the two galaxies. The resulting values of infrared luminosity agree with observations. The main mode of triggered star formation is via clusters of stars, thus we can naturally explain the formation of young, luminous star clusters observed in starburst galaxies.

scholarly journals 1D, 2D and 3D Collapse of Interstellar Clouds

1980 ◽  
Vol 58 ◽  
pp. 235-246
Author(s):  
W.M. Tscharnuter
Keyword(s):  
Star Formation ◽  
Gravitational Instability ◽  
Numerical Models ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Interstellar Clouds ◽  
B Stars ◽  
Theoretical Investigations ◽  
2D And 3D

This review is concerned with recent theoretical investigations and numerical models of star formation with varions symmetries. Observations strongly support the fact that stars condense out of cool (≈10 K) and dense (103-104 atoms/cm3) interstellar clouds due to gravitational instability and collapse. Bright, young stellar objects (0- and B-stars are always found in the vicinity of coloud complexes.

scholarly journals Low- and Intermediate-Velocity Hydrogen at Positive Galactic Latitudes

1974 ◽  
Vol 60 ◽  
pp. 631-635
Author(s):  
K. Takakubo
Keyword(s):  
Low Velocity ◽  
Interstellar Clouds ◽  
Hydrogen Emission ◽  
Intercloud Medium

Low- and intermediate-velocity Gaussian components of hydrogen emission profiles observed at positive galactic latitudes are investigated. The low-velocity hole, as called by Wesselius and Fejes (1973), is a phenomenon which appears in the layer composed of the gas emitting narrow Gaussian components but does not in that of wide components. Both Models I and II suggested by Wesselius and Fejes contradict this result. A hypothesis is proposed that a stream motion in the layer emitting wide Gaussian components, which may be identified with the intercloud medium, swept away the interstellar clouds emitting narrow Gaussian components in the region of the hole.

scholarly journals Star formation in the solar neighbourhood

2018 ◽  
Vol 14 (S345) ◽  
pp. 15-22
Author(s):  
Mika Juvela
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Milky Way ◽  
Big Bang ◽  
Solar Neighbourhood ◽  
Direct Access ◽  
Interstellar Clouds ◽  
Radio Wavelength ◽  
Eventual Collapse ◽  
The Big Bang

AbstractStar formation started as a cosmic process soon after the big bang and still continues in the Milky Way, although at a decreasing rate. The formation of dense interstellar clouds, their fragmentation and eventual collapse lead to the birth of stars. The nearby clouds provide the highest resolution for the study of this process. The progress is closely following the improvement of the infrared and radio-wavelength facilities that enables us to follow even the earliest stages of the star-formation process inside molecular clouds. On the other hand, modern numerical simulations can take into account most of the relevant physics and often provide a more direct access into the general principles of star formation. The comparison of observations and simulations is therefore essential. In this paper, will discuss star formation in the solar neighbourhood, concentrating on the prestellar phases leading up to the formation of protostars.

scholarly journals A Modern Look at ‘Interstellar Clouds’

1974 ◽  
Vol 60 ◽  
pp. 13-44
Author(s):  
Carl Heiles
Keyword(s):  
Magnetic Field ◽  
Cloud Model ◽  
Scale Structure ◽  
Doppler Velocity ◽  
Small Scale ◽  
Interstellar Gas ◽  
Interstellar Clouds ◽  
Small Scale Structure ◽  
Oriented Parallel ◽  
Intercloud Medium

We compare past and present modes of investigation of the structure of the interstellar gas. Many aspects of the interstellar cloud model are invalid.Interstellar optical absorption lines and Hi21-cm emission lines show a number of very large aggregates with properties similar to those of ‘cloud complexes’. At nonzero velocities especially for b<0°, exist optical lines which have no Hicounterparts. These are almost certainly produced in low-density gas clouds; perhaps the intercloud medium is itself cloudy.Maps of Hicolumn density taken over large velocity ranges do not reveal much small-scale structure. This fact cannot easily be reconciled with the statistical analyses of interstellar reddening. The maps do reveal large, coherent gas structures which are often filamentary in shape and at least sometimes aligned parallel to the interstellar magnetic field.Maps of Hicolumn density over small velocity ranges show much small-scale structure, often filamentary in shape. The filaments are almost universally oriented parallel to the interstellar magnetic field and have Doppler velocity gradients along their lengths. In one area the geometry of the field and gas almost exclusively suggests Alfvén-type motions.

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