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Topic: Interstellar clouds

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	Interstellar medium - Wikipedia, the free encyclopedia
		In astronomy, the interstellar medium (or ISM) is the matter and energy content that exists between the stars (or their immediate circumstellar environment) within a galaxy.
		The interstellar medium is usually divided into three phases, depending on the temperature of the gas: hot (millions of kelvins), warm (thousands of kelvins), and cold (tens of kelvins).
		Features prominent in the study of the interstellar medium include molecular clouds, interstellar clouds, supernova remnants, planetary nebulae, and similar diffuse structures.
	en.wikipedia.org /wiki/Interstellar_medium (555 words)

	Astronomy Supplement - The Interstellar Medium
		Interstellar matter is not uniformly spread throughout the Galaxy but is clumped together in interstellar clouds that vary in size and the complexity of their association in our Galaxy.
		Although most of the mass of interstellar gas is found in interstellar clouds, most of the volume of the interstellar medium consists of warm or hot diffuse gas.
		Interstellar clouds may take up as much as 4 percent of the space in the Galactic plane, with typical masses of several solar masses up to 104 M. for diffuse clouds and up to 5 x 105 M. for giant molecular clouds.
	www.physics.gmu.edu /~jevans/astr103/CourseNotes/ECText/ch16_txt.htm (6671 words)

	Cosmic chemistry in interstellar clouds points to galactic wind of low-energy cosmic rays
		Unlike dense clouds, which look fl and empty because the dust and gas block the light of stars forming inside, diffuse clouds are invisible, betrayed only by the reddening of stars whose light passes through them.
		"Interstellar chemistry is very important in that it helps determine certain properties of the galaxy, in particular the intensity of the low-energy part of the cosmic ray spectrum," said Al Glassgold, professor emeritus of physics at New York University and now adjunct professor of astronomy at UC Berkeley.
		Despite the cold, rarified gas and dust in diffuse clouds - a mere 100-300 particles per cubic centimeter - chemical reactions are ongoing, sparked by the ATP of the cosmos, H3+.
	www.eurekalert.org /pub_releases/2003-04/uoc--cci033103.php (1450 words)

	Molecular cloud - Wikipedia, the free encyclopedia
		A Molecular cloud is a type of interstellar cloud whose density and size permits the formation of molecular hydrogen, H
		This is a natural consequence of their low temperatures and high densities, and of the observed evidence that the large, star-forming clouds are confined to a large degree by their own gravity (like stars, planets, and galaxies) rather than external pressure (like clouds in the sky).
		At the same time, the clouds are known to be disrupted by some process—most likely the effects of massive stars—before a significant fraction of their mass has become stars.
	en.wikipedia.org /wiki/Molecular_cloud (449 words)

	l5body
		We believe that the interstellar dust is produced in the outer atmospheres of red giant stars and expelled into interstellar space by these stars during the later stages of their evolution.
		In the dark clouds, the interstellar dust grains block the UV starlight, permitting the molecules to survive.
		Interstellar gas is pervaded by a magnetic field, and this magnetic field tends to become stronger when compressed and to counteract gravity.
	super.colorado.edu /~astr1020/l8body.html (5117 words)

	On Campus 08/25/00--Interstellar clouds yield clues to origins of lithium
		Interstellar clouds yield clues to origins of lithium
		In the 1970s, Lambert said, scientists proposed the three elements are formed when high-energy particles called cosmic rays smash into carbon, nitrogen and oxygen nuclei in interstellar clouds and break the nuclei up into lithium, beryllium and boron.
		Scientists conducting the research over the last two winters at the McDonald Observatory discovered for the first time a pair of interstellar clouds in which the ratio of the two forms of lithium was close to one-to-one for Lithium 7 to Lithium 6.
	www.utexas.edu /opa/pubs/oncampus/00oc_issues/oc000825/oc_clouds.html (591 words)

	ESA Portal - Focus On - Is life the rule or the exception? The answer may be in the interstellar clouds
		Between stars there are huge clouds of gas and dust, the dust consisting of tiny grains typically smaller than a millionth of a millimetre.
		In specific chambers in the laboratory they reproduced the common conditions of temperature and pressure known to exist in interstellar clouds, which is, by the way, quite different from our 'normal' conditions.
		Interstellar clouds have a temperature of 260 °C below zero, and the pressure is also very low (almost zero).
	www.esa.int /export/esaCP/ESA5SQG18ZC_FeatureWeek_0.html (977 words)

	Articles - Interstellar cloud (Site not responding. Last check: 2007-10-07)
		Interstellar cloud is the generic name given to accumulations of gas, plasma and dust in our galaxy.
		Analysing the composition of interstellar clouds is achieved by studying electromagnetic radiation that we receive from them.
		Some interstellar clouds are cold and tend to give out EM radiation of large wavelengths.
	www.lastring.com /articles/Interstellar_cloud?mySession=8c159ecf41a67659549c8fa1d132cfb9 (367 words)

	Evidence for Irradiation of Interstellar Ices (Site not responding. Last check: 2007-10-07)
		While the amount of the dust, gas, and ice in dense interstellar clouds is large enough to block out most of the ultraviolet (UV) radiation field found in the diffuse interstellar medium (DISM), low levels of radiation still exist in these clouds.
		Even deep within the clouds there is a low level of background UV radiation produced by the interaction of cosmic rays with the dust, gas, and ice of the cloud.
		Interstellar photochemistry of this type may result in the production of a suite of complex organic materials, some of which may have important implications for the origin of life.
	www-space.arc.nasa.gov /~astrochm/PhotoEvidence.html (862 words)

	Scientific American: Images of astronomical nebulae look startlingly like clouds on the sky on the earth, even though ... (Site not responding. Last check: 2007-10-07)
		"Interstellar clouds are composed mostly of hydrogen, whereas terrestrial clouds are formed from water droplets or ice crystals.
		Therefore, what defines a cloud is not a specific volume of atmosphere, but rather the boundary where a phase transition occurs between vapor and liquid water.
		If the interstellar medium were uniform, then each young star would light up a spherical region of space, but such is not the case.
	www.sciam.com /print_version.cfm?articleID=0004B5E1-18A0-1C6D-84A9809EC588EF21 (786 words)

	How Stars Form - STARBASE (Site not responding. Last check: 2007-10-07)
		Interstellar clouds, or nebulae, are clouds of particles and gases in interstellar space.
		Stars are born in the interstellar medium by the gravitational collapse of gas and dust within interstellar molecular clouds which have mass many times greater than the mass of a single star.
		As long as the cloud is mostly transparent to infrared radiation, this thermal energy is radiated into space and the cloud remains relatively cool and its internal pressure low.
	www.ph.surrey.ac.uk /astrophysics/files/how_stars_form.html (1189 words)

	KTH in your Pocket: Magnetic fields and electrodynamics of dense interstellar plasma clouds
		Such clouds, which are often filamentary, consist of cold and dusty plasma and are the sites where stars and planetary systems are formed.
		The clouds are mainly studied in several molecular lines, in integrated light, and by means of polarimetric methods.
		As a complement to the observational investigations, theoretical and numerical modelling of the clouds and their electrodynamic and polarimetric properties are performed.
	www.kth.se /forskning/pocket/project.asp?id=2339 (186 words)

	Scientists Discover Two New Interstellar Molecules: Point to Probable Pathways for Chemical Evolution in Space
		The 8-atom molecule propenal and the 10-atom molecule propanal were detected in a large cloud of gas and dust some 26,000 light-years away in an area known as Sagittarius B2.
		Such clouds, often many light-years across, are the raw material from which new stars are formed.
		"Interstellar molecules are identified by means of the frequencies that are unique to the rotational spectrum of each molecule," said Lovas.
	www.nrao.edu /pr/2004/GBTMolecules (898 words)

	Introduction
		It is important to know the speeds and damping rates of the hydromagnetic waves in interstellar clouds because the waves transport angular momentum during cloud collapse to form protostars.
		There is some possible direct evidence of these hydromagnetic waves in such clouds, since they have been postulated to be the cause of the observed large widths of CO emission lines from molecular clouds (Arons and Max 1975).
		The effects of dust on the propagation of shock waves in interstellar clouds, including the rotation of the magnetic field in an obliquely propagating shock, have been considered by Pilipp and Hartquist (1994).
	www.atnf.csiro.au /pasa/14_2/cramer/paper/node1.html (889 words)

	Observations of interstellar molecules
		These enormous clouds represent the coolest (10-20 Kelvin) and densest phase of the interstellar medium, and are the largest gravitationally bound objects in a galaxy and, in fact, the largest known objects in the universe made up of molecular material.
		Interstellar molecules are observed spectroscopically either through emission lines or through absorption lines in a medium in front of a source of continuum radiation (light), such as a star or a quasar.
		The physical conditions, such as the temperature and the mass of the simulated interstellar cloud, are identical in the methanol and glycine spectra.
	www.chl.chalmers.se /~numa/astrophysics/molecules/molecules.html (4209 words)

	Dense ISM Comparison (Site not responding. Last check: 2007-10-07)
		However, there are locations in the interstellar medium, known as Dense Interstellar Molecular Clouds, where the density of interstellar material is considerably higher, at least in a relative sense (although denser than the diffuse ISM, these dense clouds still have densities that rival good laboratory vacuums!).
		Because these clouds typically contain enough material in them that they are "optically thick," this is, they absorb or scatter most of the starlight that falls on them from outside they look dark (i.e.
		As a result, most molecules in dense clouds are frozen into icy grain mantles rather than free floating gas phase molecules.
	www-space.arc.nasa.gov /~astrochm/DenseISM.html (643 words)

	C&EN: SCIENCE & TECHNOLOGY - INTERSTELLAR CHEMISTRY
		In interstellar clouds, where it's five orders of magnitude more abundant than any other molecule, it also shapes the rest of the chemistry taking place, at least in the gas phase.
		Carbon dioxide is an unusual interstellar molecule because it is observed only in the ices that form under suitable conditions around dust grains; it's not present in the gas phase.
		For instance, ices formed in lab experiments at the temperatures of interstellar clouds usually take on an amorphous structure, she says, but if they undergo any kind of processing, there's likely to be an irreversible phase change to a crystalline form.
	www.phy.syr.edu /research/surface_physics/cne_astrochemistry.htm (4217 words)

	Observations of Interstellar Clouds in the Galactic Halo (Site not responding. Last check: 2007-10-07)
		Observations of Interstellar Clouds in the Galactic Halo
		Accurate measurements of temperatures, compositions, ionization states, densities, etc., for individual interstellar clouds are required for the development of a unified model of the ISM.
		The UV spectral region is rich in absorption-line diagnostics which allow the study of interstellar matter over a wide range of physical conditions --- from the cold H I clouds, which produce strong absorption from many singly-ionized metals, to the hot 10$^5$ K gas seen in absorption from such ions as C$^{3+}$ and N$^{4+}$.
	www.aas.org /publications/baas/v27n2/aas186/abs/S3506.html (345 words)

	ESA Science & Technology: Is life the rule or the exception? The answer may be in the interstellar clouds
		The researchers started with water and a variety of simple molecules that are known to exist in the 'real' clouds, such as carbon monoxide, carbon dioxide, ammonia and hydrogen cyanide.
		Interstellar clouds have a temperature of 260 0C below zero, and the pressure is also very low (almost zero).
		Amino acids from ultraviolet irradiation of interstellar ice analogues by G. Muqoz Caro (Leiden Observatory, The Netherlands) et al.
	sci.esa.int /content/news/index.cfm?aid=1&cid=1&oid=30039 (999 words)

	The Orion Cloud and Association
		This cloud was formed when a density wave, related to the Galaxy's spiral structure, moved through the medium of the Galactic disk.
		This giant cloud, or complex of clouds, of interstellar matter and young stars contains, besides M42 and M43 and the nebulosity associated with them (NGC 1973-5-7), a number of famous objects: Barnard's Loop, the Horsehead Nebula region (also containing NGC 2024 = Orion B), and the reflection nebulae around M78.
		They must have left the Orion cloud about 2--5 million years ago, and it is speculated that they might have speeded up somehow during supernova explosions (perhaps of companion stars in multiple systems).
	www.seds.org /messier/more/oricloud.html (691 words)

	Molecular oxygen in interstellar clouds
		The abundances of chemical species and the temperature profile throughout a molecular cloud are obtained by solving, in a self-consistent way, a radiative transfer equation for UV photons - taking into account absorption by both dust and gas - the chemical balance equations and a thermal balance equation.
		Table 1 shows the results of the model for three standard clouds: a diffuse one, a translucent one and a dense one.
		The cooling of a molecular cloud, plotted in Figure 4, occurs through fine structure emission of atoms and ions and rotational transitions of molecules.
	www.mrao.cam.ac.uk /yerac/marechal/marechal.html (1020 words)

	Sugar in Space (Site not responding. Last check: 2007-10-07)
		Conditions in interstellar clouds may, in some cases, mimic the conditions on the early Earth, so studying the chemistry of interstellar clouds may help scientists understand how bio-molecules formed early in our planet's history.
		Though very rarefied by Earth standards, these interstellar clouds are the sites of complex chemical reactions that occur over hundreds of thousands or millions of years.
		This is the cloud in which scientists using the 12 Meter Telescope detected the simple sugar molecule glycolaldehyde.
	spacescience.com /headlines/y2000/ast20jun_1.htm?list (1009 words)

	Interstellar clouds (Site not responding. Last check: 2007-10-07)
		There is some chance that the Solar System will cross small dense clouds that have diameters up to 100 times the distance from the Earth to the Sun.
		Our interstellar environment may thus be important for the short and long-term prospects for life on Earth.
		Even though there is still some work to be done before it will be possible to construct a 'Galactic weather forecast', it is clear that for the past 200,000 years we have been in a favourable environment that has not altered our climate significantly.
	homepage.ntlworld.com /brian.kilby/astro/2000/apr/clouds.html (219 words)

	[No title]
		Interstellar Clouds A. effect - blocks light 1.
		interstellar extinction - reduction in intesity of light passing through material 3.
		Nebula - clouds of interstellar gas & dust a.
	www.mindspring.com /~jeff.wilson/docs/notes/starlife.txt (1722 words)

	Wide-Field Optical Imaging of Interstellar Cirrus Clouds (Site not responding. Last check: 2007-10-07)
		There is a broad range of optical colors from cloud to cloud and even within different areas of a given cloud.
		In the ``blue'' cirrus clouds, the ratio of B to 100$\mu m$ surface brightness over most regions is consistent with that expected if the same grains that emit the bulk of the infrared radiation are the primary scatterers.
		The relationship between the optical and infrared emission in the ``red'' clouds is found to be much more complex suggesting that the different grain species in the clouds may be inhomogeneously mixed.
	www.aas.org /publications/baas/v26n4/aas185/abs/S1207.html (332 words)

	Cell Membrane-Like Organic Vesicles Formed in Conditions Mimicking Interstellar Clouds?
		The study began by using a gas mixture of water, methane, ammonia and carbon monoxide, which the authors claim are the prevalent gases found in interstellar clouds.
		However, these clouds are also known to contain significant amounts of carbon dioxide, which was not included in their mixture.
		In interstellar space, everything is cold and any frozen gases would not be expected to get concentrated on any solid substrate in this manner, except under extremely rare conditions, none of which I can think of at the moment.
	www.geocities.com /CapeCanaveral/Lab/6562/evolution/astrobiology.html (1296 words)

	Nebulae
		Diffuse nebulae are clouds of interstellar matter, namely thin but widespread agglomerations of gas and dust.
		Now that the nature of nebulae as interstellar masses of gas and dust is known, there are still several classification schemes.
		The first of these classes typically includes clouds of interstellar matter of a mass of several 100 or several 1,000 stars, while the latter is related to one specific star in advanced state of evolution, at or just beyond the end of its nuclear life.
	seds.lpl.arizona.edu /messier/nebula.html (717 words)

	Rednova NEWS \| Cosmic Chemistry Inside Interstellar Clouds (Site not responding. Last check: 2007-10-07)
		Cosmic chemistry inside interstellar clouds points to galactic wind of low-energy cosmic rays, UC Berkeley researchers claim
		UC Berkeley -- Berkeley - A bit of Earth-bound chemistry has led scientists at the University of California, Berkeley, to conclude that there is an unsuspected wind of low-energy cosmic ray particles blowing through the galaxy.
		It is operated by the Joint Astronomy Centre in Hilo, Hawaii, on behalf of the UK Particle Physics and Astronomy Research Council.
	www.rednova.com /modules/news/tools.php?tool=print&id=1336 (1503 words)

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