scholarly journals Large HI clouds in the Galaxy

1964 ◽  
Vol 20 ◽  
pp. 126-130
Author(s):  
R. X. McGee
Keyword(s):  
Interstellar Medium ◽  
Interstellar Clouds ◽  
Structural Details ◽  
The Galaxy

van de Hulst (1958), in giving representative sizes of the structural details of the interstellar medium, lists the dimensions of a typical cloud, seen in 21-cm emission, as 20–70 pc but warns that we should not be surprised to find different “sizes of interstellar clouds” determined from different sets of data.

scholarly journals DIBs, Interstellar Dust, and Extinction

2013 ◽  
Vol 9 (S297) ◽  
pp. 147-152 ◽  
Author(s):  
G. C. Clayton
Keyword(s):  
Interstellar Medium ◽  
Interstellar Dust ◽  
Dust Grains ◽  
Weak Correlation ◽  
Interstellar Clouds ◽  
The Galaxy ◽  
The Relationship

AbstractThe relationship between DIBs and dust is still unknown. The correlation between reddening and DIB strength means that the DIBs are mixed in with the dust and gas in interstellar clouds. The DIBs are relatively stronger in the diffuse interstellar medium than in dense clouds. There is only a weak correlation between the DIBs and the UV extinction parameters including the 2175 Å bump strength and the far-UV rise. In addition, the bump dust grains are sometimes polarized, while the DIBs are not. However, observations of DIBs in the SMC show that when the 2175 Å bump is weak or missing so are the DIBs. Two of the four sightlines that deviate strongly from the CCM UV extinction in the Galaxy show weak DIBs.

Interstellar Probe: A Mission to the Heliospheric Boundary and Interstellar Medium for the Next Decade

2021 ◽  
Author(s):  
Pontus Brandt ◽  
Ralph McNutt ◽  
Elena Provornikova ◽  
Carey Lisse ◽  
Kathleen Mandt ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Space Exploration ◽  
Launch Vehicles ◽  
Applied Physics ◽  
Gravity Assist ◽  
Interstellar Clouds ◽  
The Galaxy ◽  
Historic Data ◽  
Near Term ◽  
Interstellar Probe

<p>An Interstellar Probe mission to the Very Local Interstellar Medium (VLISM) would bring new scientific discoveries of the mechanisms upholding our vast heliosphere and directly sample the unexplored Local Interstellar Clouds that our Sun is moving through in relatively short galactic timescales. As such, it would represent Humanity's first explicit step in to the galaxy and become perhaps NASA's boldest step in space exploration. Such a mission has been discussed and studied since 1960, but the stumbling block has often been propulsion. Now this hurdle has been overcome by the availability of new and larger launch vehicles. An international team of scientists and experts are now progressing towards the final year of a NASA-funded study led by The Johns Hopkins University Applied Physics Laboratory (APL) to develop pragmatic example mission concepts for an Interstellar Probe with a nominal design lifetime of 50 years. Together with the Space Launch System (SLS) Office at the NASA Marshall Space Flight Center, the team has analyzed dozens of launch configurations and demonstrate that asymptotic speeds in excess of 7.5 Astronomical Units (AU) per year can be achieved using existing or near-term propulsion stages with a powered or passive Jupiter Gravity Assist (JGA). These speeds are more than twice that of the fastest escaping man-made spacecraft to date, which is Voyager 1 currently at 3.59 AU/year. An Interstellar Probe would therefore reach the Termination Shock (TS) in less than 12 years and cross the Heliopause into the VLISM after about 16 years from launch.</p><p>In this presentation we provide an overview and update of the study, the science mission concept, discuss the compelling discoveries that await, and the associated example science payload, measurements and operations ensuring a historic data return that would push the boundaries of space exploration by going where no one has gone before.</p>

scholarly journals Giant molecular clouds in the galaxy: distribution, mass, size and age

1979 ◽  
Vol 84 ◽  
pp. 35-52 ◽  
Author(s):  
P. M. Solomon ◽  
D. B. Sanders ◽  
N. Z. Scoville
Keyword(s):  
Interstellar Medium ◽  
Molecular Clouds ◽  
Galactic Disk ◽  
Free Fall ◽  
Major Constituent ◽  
Giant Molecular Clouds ◽  
Interstellar Clouds ◽  
Dominant Component ◽  
The Galaxy ◽  
Galactic Distribution

Millimeter wave observations of emission from the CO molecule have become, over the past eight years, the dominant method for determining the physical properties of dense interstellar clouds, composed primarily of molecular hydrogen and for exploring the structure and kinematics of the galactic disk. In this paper we briefly review the CO survey results in the literature (Section 2) and then present new results (Section 3-7) of an extensive 13CO and 12CO survey of the galactic distribution, size, mass and age of molecular clouds. The interpretation of this survey leads to a new picture of the interstellar medium dominated by very massive stable long-lived clouds which we refer to as Giant Molecular Clouds. We find that Giant Molecular Clouds (GMC's) with M = 105–3 × 106M⊙ are a major constituent of the galactic disk, the dominant component of the interstellar medium in the galaxy interior to the sun and the most massive objects in the galaxy. We find that the interstellar medium and star formation are dominated by massive gravitationally bound clouds in which stars and associations are forming but at a very low rate in comparison to the free fall time. The galactic distribution of the molecules as traced by CO emission is interpreted as the distribution of GMC's. As the most massive objects in the galaxy they are also basic to the dynamics of the disk.

scholarly journals Kiloparsec Scale Radio Structure in Active Galaxies

1983 ◽  
Vol 6 ◽  
pp. 467-480 ◽  
Author(s):  
A. S. Wilson
Keyword(s):  
Interstellar Medium ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Active Galaxies ◽  
Radial Acceleration ◽  
Radio Structure ◽  
Interstellar Clouds ◽  
Ram Pressure ◽  
The Galaxy

AbstractA substantial fraction of active galaxies contain linear radio sources with sizes of a few hundreds or thousands of parsecs. Such sources are found in essentially all classes of active galactic nuclei, including Seyfert galaxies of both types, X-ray selected active nuclei, radio galaxies and quasars. The radio emission is clearly energised by the active nucleus, probably in the form of a jet. A number of observable consequences of the interaction of the jet with the interstellar medium of the galaxy are discussed. These processes include jet disruption by instabilities, acceleration of cosmic rays by shocks or turbulence, ionization and radial acceleration of interstellar clouds, creation of a hot thermal component through the agency of shock waves and bending of the jet by the ram pressure of a rotating interstellar medium.

scholarly journals Abundances in the Gaseous Galactic Halo

1998 ◽  
Vol 11 (1) ◽  
pp. 86-89
Author(s):  
Ulysses J. Sofia
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
High Velocity ◽  
Galactic Halo ◽  
Solar Neighborhood ◽  
Local Interstellar Medium ◽  
The Galaxy ◽  
Metal Abundances ◽  
High Velocity Clouds

Abstract The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.

scholarly journals On the Mechanism of H2 Formation in the Interstellar Medium

1987 ◽  
Vol 120 ◽  
pp. 167-169
Author(s):  
Valerio Pirronello
Keyword(s):  
Interstellar Medium ◽  
Molecular Hydrogen ◽  
Formation Rate ◽  
Cosmic Ray ◽  
Interstellar Clouds ◽  
H2 Formation ◽  
Reduced Mobility

The problem of the formation of molecular hydrogen in interstellar clouds is revisited. the role played by cosmic ray bombardment under certain circumstances is considered mainly in the light of the low formation rate of H2 on grains due to the reduced mobility of adsorbed H atoms on their amorphous surfaces at interstellar temperatures.

scholarly journals Astrophysical MHD turbulence: confluence of observations, simulations, and theory

2012 ◽  
Vol 8 (S294) ◽  
pp. 325-336 ◽  
Author(s):  
Blakesley Burkhart ◽  
Alex Lazarian
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Magnetic Reconnection ◽  
Particle Transport ◽  
Recent Progress ◽  
Critical Component ◽  
Dynamo Theory ◽  
Mhd Turbulence ◽  
The Galaxy

AbstractMagnetohydrodynamic (MHD) turbulence is a critical component of the current paradigms of star formation, dynamo theory, particle transport, magnetic reconnection and evolution of the ISM. In order to gain understanding of how MHD turbulence regulates processes in the Galaxy, a confluence of numerics, observations and theory must be imployed. In these proceedings we review recent progress that has been made on the connections between theoretical, numerical, and observational understanding of MHD turbulence as it applies to both the neutral and ionized interstellar medium.

The Unidentified Infrared Bands in the Diffuse Interstellar Medium across the Galaxy Based on theInfrared Telescope in SpaceMid‐Infrared Spectrometer Observation

2004 ◽  
Vol 609 (1) ◽  
pp. 203-219 ◽  
Author(s):  
Itsuki Sakon ◽  
Takashi Onaka ◽  
Daisuke Ishihara ◽  
Takafumi Ootsubo ◽  
Issei Yamamura ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
The Galaxy ◽  
Infrared Spectrometer

scholarly journals Unidentified infrared bands in the interstellar medium across the Galaxy

2003 ◽  
Vol 405 (3) ◽  
pp. 999-1012 ◽  
Author(s):  
J. Kahanpää ◽  
K. Mattila ◽  
K. Lehtinen ◽  
C. Leinert ◽  
D. Lemke
Keyword(s):  
Interstellar Medium ◽  
The Galaxy

Pulsars and Interstellar Scintillations

2000 ◽  
Vol 177 ◽  
pp. 539-544
Author(s):  
Y. Gupta
Keyword(s):  
Interstellar Medium ◽  
Electron Density ◽  
Density Fluctuations ◽  
Current Understanding ◽  
Pulsar Emission ◽  
The Galaxy ◽  
Electron Density Fluctuations

AbstractIn this paper, I review our current understanding of interstellar scintillations (ISS) of pulsars. The emphasis is on new results that have appeared during the last five years. The topics covered include (i) review of the understanding of refractive ISS (ii) the shape of the spectrum of electron density fluctuations in the interstellar medium (iii) the distribution of scattering plasma in the Galaxy (iv) resolving pulsar emission regions using ISS and (v) ISS and pulsar velocities.

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