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Topic: Giant Molecular Cloud

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	Dark nebula - Wikipedia, the free encyclopedia
		A dark nebula is a large molecular cloud which appears as a star-poor region where the dust of interstellar medium seems to be concentrated.
		The cloud cores are completely hidden from view and would be undetectable except for the microwave emissions from their constituent molecules.
		This radiation is not absorbed by dust and readily escapes the cloud.
	en.wikipedia.org /wiki/Giant_Molecular_Cloud (421 words)

	Molecular cloud - Wikipedia, the free encyclopedia
		Catalogues of clouds exhibit that most of the molecular mass is concentrated in the most massive object, which comprise several million solar masses.
		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.
		Molecular clouds, and especially "Giant" molecular clouds (GMCs), are often the home of astronomical masers.
	en.wikipedia.org /wiki/Molecular_cloud (525 words)

	Cool Cosmos
		Molecular clouds that exceed the mass of 100,000 suns are called giant molecular clouds.
		Giant molecular clouds are the largest inhabitants of galaxies, reaching up to 300 light years in diameter.
		Molecular clouds are very cold, having temperatures ranging from about -440 to -370 degrees Fahrenheit (-263 to -223 degrees Celcius or 10 to 50 degrees Kelvin).
	coolcosmos.ipac.caltech.edu /cosmic_classroom/cosmic_reference/molecular_clouds.html (416 words)

	Untitled Document
		Molecular clouds are highly complicated structures that maintain inside of them a battle of opposing forces which produce pressure and turbulence.
		The molecular cloud is made up of very dense material which must be supported by some forces to prevent self-gravity from collapsing upon itself.
		Scientific observation indicates that turbulence occurs in the cloud fluid that is in the nature of supersonic character motion.
	ffden-2.phys.uaf.edu /212_fall2003.web.dir/Ihor_Bashchuk/WebProject/Pages/Mclouds.htm (252 words)

	Oort Cloud
		The Oort cloud is an immense spherical cloud surrounding the planetary system and extending approximately 3 light years, about 30 trillion kilometers from the Sun.
		The structure of the cloud is believed to consist of a relatively dense core that lies near the ecliptic plane and gradually replenishes the outer boundaries, creating a steady state.
		The Oort cloud is the source of long-period comets and possibly higher-inclination intermediate comets that were pulled into shorter period orbits by the planets, such as Halley and Swift-Tuttle.
	www.solarviews.com /eng/oort.htm (710 words)

	Ev of Stars1 Questions
		A giant molecular cloud is a dense, cold interstellar cloud.
		As the cloud collapses, the pressure of the gas in the cloud increases.
		The temperature inside a giant molecular cloud is 10 K and the density is a few thousand atoms per cubic inch.
	webs.wichita.edu /astronomy/wqquestions/evof1Quest.htm (1161 words)

	The case of a giant molecular cloud. (Site not responding. Last check: 2007-11-01)
		The energy/momentum loss factor induced by the presence of very long giant flows would presumably be rather low in the case of a giant molecular cloud, since even the longest flows are short compared to the diameter of a giant molecular cloud, and most flows will not stick out of the cloud.
		Even for a clearly elongated cloud such as Orion A, the energy loss to the interstellar medium outside the cloud is probably minor, since even the extent of the cloud perpendicular to the major axis is of order 10-20 pc.
		The assumption of virial equilibrium is probably well justified here, since giant molecular clouds are generally observed to be in virial equilibrium (e.g., Blitz 1993).
	www.ifa.hawaii.edu /users/stanke/thesis/chap7_10.html (466 words)

	Orioncloudtext
		The Orion Molecular cloud is comprised of two distinct giant molecular clouds known as the Orion A and Orion B clouds, named after the HII regions formed within them (Orion A = M42, Orion B = NGC 2024).
		A dense ridge-like structure exists within the molecular gas of the Orion A and B clouds and represents the location of distinct cores of hot gas and dust where concentrated star formation is occurring.
		Star formation in the Orion clouds has almost certainly occurred by way of external sequential triggering where the supernovae and stellar winds of one generation have triggered the collapse of adjacent molecular clouds and the subsequent formation of a new generation of stars.
	www.robgendlerastropics.com /Orioncloudtext.html (670 words)

	01.09.2002 - Radio mapping of molecular clouds in nearby spiral galaxy helps astronomers unravel first steps in how ...
		The star formation areas, known as giant molecular clouds, should be rotating rapidly, spinning up as they collapse like spinning ice skaters drawing in their arms.
		Nearly every giant molecular cloud in M33 within the survey region was detected, and the clouds have sizes and shapes similar to those found in our own galaxy.
		Blitz said that only a tiny proportion of gas in the molecular cloud - only one in 10 million atoms in the densest part of the cloud - is charged and thus tied to the magnetic field.
	www.berkeley.edu /news/media/releases/2002/01/09_galxy.html (1008 words)

	Overview of Molecular Astrophysics and Star Formation
		All stars, as far as we know, are born from the gravitational collapse of the core of a molecular cloud.
		Molecular clouds are regions of relatively dense interstellar gas and dust that can shield their contents against the destructive ambient ultraviolet (UV) radiation field.
		Much data has been gathered on molecular clouds in relation to their ability to form stars, mostly via detection of the molecular emission lines at (sub)millimeter wavelengths.
	loke.as.arizona.edu /~ckulesa/research/overview.html (986 words)

	Chandra :: Educational Materials :: Stellar Evolution :: Stellar Evolution - Cycles of Formation and Destruction
		The molecular clouds are puffy and lumpy, with diameters ranging from less than 1 light-year to about 300 Light Years and contain enough gas to form from about 10 to 10 million stars like our Sun.
		Since the molecules in these clouds do not emit optical light, but do release light at radio wavelengths, radio telescopes are necessary to trace the molecular gases and study their physical properties.
		Star-forming molecular clouds are mostly found along spiral arms, as seen in the CO molecular map showing the distribution of these clouds in the Milky Way Galaxy.
	chandra.harvard.edu /edu/formal/stellar_ev/story/index2.html (651 words)

	Introduction (Site not responding. Last check: 2007-11-01)
		The Carina HII region/molecular cloud complex is an excellent region for studying the interaction of massive stars with their parental Giant Molecular Cloud (GMC).
		The area between the southern and northern CO clouds is centred on the Keyhole Nebula, a dense dark cloud northwest of
		CO emission is thermalised in both low- and high-density gas and therefore is suitable for tracing the overall distribution and velocity structure of the molecular cloud.
	www.atnf.csiro.au /pasa/15_2/brooks/paper/node1.html (695 words)

	UC Berkeley astronomers find magnetic Slinky in constellation of Orion
		Interstellar clouds are dense regions embedded in a much lower-density external medium, but the "dense" interstellar clouds are, by Earth standards, a perfect vacuum.
		Astronomers have known for some time that many molecular clouds are filamentary structures whose shapes are suspected to be sculpted by a balance between the force of gravity and magnetic fields.
		Using the GBT, Robishaw and Heiles observed radio waves along slices across the Orion Molecular Cloud and found that the magnetic field reversed its direction, pointing towards the Earth on the upper side of the cloud and away from it on the bottom.
	www.eurekalert.org /pub_releases/2006-01/uoc--uba010906.php (1018 words)

	The Weather Forecast: All Cloudy and Heavy Meteoric Rainfall
		Of course, the Doomsday Cloud that will bring about the end of the world is quite different from those puny pieces of wadding you see up in the sky every day.
		Giant Molecular Clouds are, in fact, stars in the making.
		Giant Molecular Clouds have a reputation for messing up the atmosphere of each Earth-like planet they encounter.
	www.exitmundi.nl /gmc.htm (834 words)

	NASA - NASA Study Suggests Giant Space Clouds Iced Earth
		Eons ago, giant clouds in space may have led to global extinctions, according to two recent technical papers supported by NASA's Astrobiology Institute.
		In a more likely scenario, less dense giant molecular clouds may have enabled charged particles to enter Earth's atmosphere, leading to destruction of much of the planet's protective ozone layer.
		Moderately dense space clouds are huge, and the solar system could take as long as 500,000 years to cross one of them.
	www.nasa.gov /home/hqnews/2005/mar/HQ_05066_giant_clouds.html (677 words)

	[No title] (Site not responding. Last check: 2007-11-01)
		These giant molecular clouds are quite stable, due to their electrically neutral state as well as their extremely low temperatures.
		When a molecular cloud of hydrogen, such as the one found in the 30 Doradus region, reaches what is called the Jean's Limit, or Jeans Mass, our cloud will collapse in on itself.
		In the simplest cases, the timescale on which such a collapse occurs is actually independent of the radius of the cloud, and is totally dependent on the density of the cloud.
	mail.rochester.edu /~amoore6/?S=D (2494 words)

	Carpenter & Sanders, The W51 Giant Molecular Cloud (Site not responding. Last check: 2007-11-01)
		Published absorption line spectra indicate that the fifth prominent continuum source (G49.4-0.3) is located behind the W51 molecular cloud.
		The W51 GMC is among the upper 1% of clouds in the Galactic disk by size and the upper 5-10% by mass.
		The W51 GMC is also similar to other clouds in that most of the molecular mass is contained in a diffuse envelope that is not currently forming massive stars.
	www.ifa.hawaii.edu /publications/preprints/98preprints/Carpenter_98-43.html (278 words)

	Scientists Discover Sugar In Space
		This is the cloud in which scientists using the 12 Meter Telescope detected the simple sugar molecule glycolaldehyde.
		The discovery of the sugar molecule glycolaldehyde in a giant cloud of gas and dust near the center of our own Milky Way Galaxy was made by scientists using the National Science Foundation's 12 Meter Telescope, a radio telescope on Kitt Peak, Arizona.
		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.
	www.spacedaily.com /news/life-00zi.html (813 words)

	Cornell News: SWAS results
		Because the interstellar clouds are considered to be nurseries for star formation, the SWAS science team is attempting to understand the chemical reactions that affect star birth.
		Both water and molecular oxygen have been considered to be essential constituents of the molecular clouds from which stars form.
		The almost complete absence of molecular oxygen, Goldsmith says, is harder to explain because the molecule doesn't freeze in the same way as water and, thus, would not be in frozen form on dust grains.
	www.news.cornell.edu /releases/Jan01/SWAS.Goldsmith.deb.html (829 words)

	NASA's Solar System Exploration: Planets: Oort Cloud: Overview
		The vast distance of the Oort cloud is considered to be the outer edge of the Solar System - where the Sun's orb of physical and gravitational influence ends.
		Tidal and molecular forces also contribute to influencing the orbits of bodies within the Oort Cloud.
		A giant molecular cloud is by far more massive than the Sun.
	solarsystem.nasa.gov /planets/profile.cfm?Object=OortCloud&Display=OverviewLong (364 words)

	Lives and Deaths of Stars
		A giant molecular cloud is a large, dense gas cloud (with dust) that is cold enough for molecules to form.
		Fragments of giant molecular clouds with tens to hundreds of solar masses of material a piece will start collapsing for some reason all at about the same time.
		Possible trigger mechanisms could be a shock wave from the explosion of a nearby massive star at its death or from the passage of the cloud through regions of more intense gravity as found in the spiral arms of spiral galaxies.
	www.astronomynotes.com /evolutn/s3.htm (1146 words)

	Tutorial Question Week 2
		Suppose a giant molecular cloud (or GMC), with a mass of 10^36 kg, converts 1% of its mass into stars during an encounter with an interstellar shock wave.
		It can be shown that the maximum size of a cloud for collapse to occur varies as L = 10^7 (T/rho)^0.5, where L is the size (in m), T is the gas temperature (in K) and rho is the gas density (in kg/m^3).
		A core of a giant molecular cloud (GMC) has a radius of about 1 parsec, a temperature between 30 and 100K, and a particle number density of about 10^10 m^-3.
	www.phys.unsw.edu.au /astro/seti/tq/tq2.html (644 words)

	Giant Gas Cloud Made of Atoms From First Stars
		Astronomers studying the most distant quasar yet found in the Universe have discovered a massive reservoir of gas containing atoms made in the cores of some of the first stars ever formed.
		It means that, even at a very early time in the history of the Universe, galaxies already had huge amounts of molecular gas that would eventually form new generations of stars," said Chris Carilli, of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico.
		The amount of molecular gas in the galaxy -- a mass more than 10 billion times that of the Sun -- tells the scientists that things were happening quickly in the early Universe.
	www.nrao.edu /pr/2003/j1148 (1331 words)

	Water in Orion (Site not responding. Last check: 2007-11-01)
		A team of U.S. astronomers, including a member of the Harvard-Smithsonian Center for Astrophysics, has discovered a large concentration of water vapor within a cloud of interstellar gas close to the Orion nebula, using a satellite launched and operated by the European Space Agency with the participation of NASA.
		The concentration of water vapor measured in Orion is twenty times larger than that measured previously in other interstellar gas clouds, and may provide an important clue to the origin of water in the solar system.
		The astronomers observed water vapor within the Orion Molecular Cloud, a giant interstellar gas cloud composed primarily of hydrogen molecules, using the European Space Agency's Infrared Space Observatory satellite, ISO, which was launched in November 1995.
	cfa-www.harvard.edu /cfa/hotimage/worion.html (725 words)

	Radio spectroscopy of giant molecular cloud cores
		Harju, Lehtinen, Booth and Zinchenko have conducted a survey of thermal SiO line emission towards galactic giant molecular cloud cores in order to study the characteristics of shocks associated with molecular line masers and embedded far-infrared sources.
		It was found that for flux and luminosity limited samples the SiO detection rate is higher in the inner 7 kpc from the galactic centre than elsewhere.
		Although the line shapes in general agree with a model where the emission arises from turbulent wakes behind bow-shocks, there are a large number of cores with symmetric, relatively narrow profiles.
	www.astro.helsinki.fi /report/1998/node15.html (349 words)

	The Orion Cloud and Association (Site not responding. Last check: 2007-11-01)
		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)

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