1. Interstellar Medium - Wikipedia, The Free Encyclopedia In astronomy, the interstellar medium (or ISM) is the gas and dust that pervade interstellar space the matter that exists between the star systems within a galaxy. http://en.wikipedia.org/wiki/Interstellar_medium

Interstellar medium From Wikipedia, the free encyclopedia Jump to: navigation search "Interstellar" redirects here. For other uses, see Interstellar (disambiguation) The distribution of ionized hydrogen Haffner et al. 2003 In astronomy , the interstellar medium (or ISM ) is the gas and dust that pervade interstellar space: the matter that exists between the star systems within a galaxy . It fills interstellar space and blends smoothly into the surrounding intergalactic space . The energy that occupies the same volume, in the form of electromagnetic radiation , is the interstellar radiation field The interstellar medium consists of an extremely dilute (by terrestrial standards) mixture of ions atoms molecules , larger dust grains cosmic rays , and (galactic) magnetic fields. The matter consists of about 99% gas and 1% dust by mass Densities range from a few thousand to a few hundred million particles clarification needed per cubic meter with an average value in the Milky Way Galaxy of a million particles per cubic meter (1 atom per cubic centimeter). The Sun , for example, is presently traveling through the Local Interstellar Cloud (0.1 atoms/cc), within the

2. Interstellar Medium: Facts, Discussion Forum, And Encyclopedia Article Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the Earth's atmosphere http://www.absoluteastronomy.com/topics/Interstellar_medium

Home Discussion Topics Dictionary ... Login Interstellar medium Interstellar medium Topic Home Discussion Definition Discussion Ask a question about ' Interstellar medium Start a new discussion about ' Interstellar medium Answer questions from other users Full Discussion Forum Encyclopedia In astronomy Astronomy Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the Earth's atmosphere... , the interstellar medium (or ISM ) is the gas Gas Gas is one of three classical states of matter. Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons are... and dust Cosmic dust Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 mm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar... that pervade interstellar space: the matter Matter Matter is a general term for the substance of which all physical objects are made. Typically, this includes atoms and other particles which have mass. However in practice there is no single correct scientific meaning; each field uses the term in different and often incompatible ways...

3. Interstellar Medium And Galactic Center | University Of Iowa Astrophysics | Robe View of the central 50 pc (~150 light years) of the Galactic center showing ionized gas (traced by Paschen alpha emission observed by Hubble Space Telescope), hot plasma http://www-astro.physics.uiowa.edu/research/interstellar_medium.html

University of Iowa Astrophysics Department of Physics and Astronomy Site Navigation [Skip] Home Faculty Research ... Contact Interstellar Medium and Galactic Center Previous Next List Galactic Center Composite Image View of the central 50 pc (~150 light years) of the Galactic center showing ionized gas (traced by Paschen alpha emission observed by Hubble Space Telescope), hot plasma (traced in the X-ray by the Chandra X-ray Observatory) and warm dust (traced by mid-infrared radiation by the Spitzer Space Telescope). Video trip through ISM QT_WriteOBJECT_XHTML ( "../_Media/zoom_from_the_milky_way_gal.mov", "200", "128", "", "autoplay","false", "controller","true", "kioskmode","false", "loop","true", "scale","tofit", "type","video/quicktime" ); Movie illustrating a zoom animation from outside the Milky Way galaxy through the interstellar medium to the Sun's heliosphere (courtesy NASA/IBEX mission). ROSAT Soft X ray All-Sky Map ROSAT map of the 1/4 keV soft X-ray background. (Snowden et al. 1995, ApJ, 454, 643) Simulated soft X ray spectrum Simulation of the rocket observation of the soft X-ray background at low galactic latitude (lower plots) and high galactic latitude. The panels on the left are the input models containing charge exchange

4. Interstellar Medium - New World Encyclopedia The distribution of ionized hydrogen (known by astronomers as H II from old spectroscopic terminology) in the parts of the galactic interstellar medium visible from the Earth's http://www.newworldencyclopedia.org/entry/Interstellar_medium

Interstellar medium From New World Encyclopedia Jump to: navigation search Previous (Interoperability) Next (Interview) Ready "Interstellar" redirects here. In astronomy , the interstellar medium (or ISM ) is the gas and dust that pervade interstellar space: the matter that exists between the stars within a galaxy . It fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy, in the form of electromagnetic radiation , that occupies the same volume is the interstellar radiation field The ISM plays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales. Stars form within the densest regions of the ISM, molecular clouds, and replenish the ISM with matter and energy through planetary nebulae, stellar winds , and supernovae. This interplay between stars and the ISM helps determine the rate at which a galaxy depletes its gaseous content, and therefore its lifespan of active star formation. Contents Overview of characteristics Interstellar matter The three-phase model Structures ... Credits Overview of characteristics The interstellar medium consists of an extremely dilute (by terrestrial standards) mixture of ions atoms molecules , larger dust grains, cosmic rays , and (galactic) magnetic fields.

5. Interstellar Medium - Slider The interstellar medium (or ISM) is a term used in astronomy to describe the matter and energy content that exists between the stars (or their immediate circumstellar environment http://enc.slider.com/Enc/Interstellar_medium

Advanced Help Encyclopedia Directory Encyclopaedia I In Ina ... Inz Interstellar medium The interstellar medium (or ISM ) is a term used in astronomy to describe the matter and energy content that exists between the stars (or their immediate "circumstellar" environment) within a galaxy . The ISM pays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales. Stars themselves form within cold regions of the ISM, and replenish the ISM with matter and energy through stellar winds and supernovae . In turn, this interplay between stars and the ISM sets the rate at which a galaxy depletes its gaseous content and therefore determines its lifespan of active star formation. The ISM consists of an extremely dilute (by terrestrial standards) mixture of atoms molecules dust electromagnetic radiation ... cosmic rays , and the magnetic field . The matter normally consists of about 99% gas particles and usually 1% of dust. It fills interstellar space. This mixture is usually extremely tenuous, with typical gas densities ranging from a few single to a few hundreds of a particles per cubic centimeter. As a results of primordial nucleosynthesis, the gas is roughly 90% hydrogen and 10% helium , with additional elements (" metals " in astronomical parlance) present in trace amounts.

6. Interstellar Medium Interstellar medium. The interstellar medium (or ISM) is a term used in astronomy to describe the rarefied gas that exists between the stars (or their immediate circumstellar http://www.fact-index.com/i/in/interstellar_medium.html

Main Page See live article Alphabetical index Interstellar medium The interstellar medium (or ISM ) is a term used in astronomy to describe the rarefied gas that exists between the stars (or their immediate "circumstellar" environment) within a galaxy . This gas is usually extremely tenuous, with typical densities ranging from a few tens to a few hundredths of a particle per cubic centimeter. Generally the gas is roughly 90% hydrogen and 10% helium, with additional elements (" metals ", in astronomical parlance) present in trace amounts. The interstellar medium is usually divided into three phases , depending on the temperature of the gas: hot (millions of kelvin ), warm (thousands of kelvin ), and cold (tens of kelvin ). This "three-phase" model of the ISM was initially developed by McKee and Ostriker in a 1977 paper, which has formed the basis for further study over the past quarter-century. The relative proportions of the phases is still a matter of considerable contention in scientific circles. Features prominent in the study of the interstellar medium include molecular clouds, interstellar clouds, supernova remnants planetary nebulae , and similar diffuse structures.

7. Interstellar Medium A selection of articles related to Interstellar Medium Interstellar medium Encyclopedia II Interstellar medium - History. The term interstellar appears to be have been first used http://www.experiencefestival.com/interstellar_medium

8. Interstellar Medium The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. Whilst the ISM refers to the matter (interstellar matter http://www.sciencedaily.com/articles/i/interstellar_medium.htm

Science Reference Share Blog Print Email Bookmark Interstellar medium The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. See also: Astrophysics Nebulae Galaxies Stars ... Dark Matter Whilst the ISM refers to the matter (interstellar matter, also abbreviated by ISM) that exists between the stars within a galaxy, the energy, in the form of electromagnetic radiation, that occupies the same volume is called the interstellar radiation field (or ISRF). The ISM consists of an extremely dilute (by terrestrial standards) plasma, gas and dust, consisting of a mixture of ions, atoms, molecules, larger dust grains, electromagnetic radiation, cosmic rays, and magnetic fields. The matter consists of about 99% gas and 1% dust by mass. It fills interstellar space. This mixture is usually extremely tenuous, with typical gas densities ranging from a few hundred to a few hundred million particles per cubic meter. As a result of primordial nucleosynthesis, the gas is roughly 90% hydrogen and 10% helium by number, with additional elements ("metals" in astronomical parlance) present in trace amounts. The ISM plays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales. Stars form within the densest regions of the ISM, molecular clouds, and replenish the ISM with matter and energy through planetary nebulae, stellar winds, and supernovae.

9. Interstellar Medium Summary And Analysis Summary | BookRags.com Interstellar medium summary with 13 pages of lesson plans, quotes, chapter summaries, analysis, encyclopedia entries, essays, research information, and more. http://www.bookrags.com/Interstellar_medium

10. Interstellar Medium | Ask.com Encyclopedia The distribution of ionized hydrogen (known by astronomers as H II from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earth's http://www.ask.com/wiki/Interstellar_medium?qsrc=3044

11. Interstellar Medium - Space Wiki In astronomy, the interstellar medium (or ISM) is the matter (interstellar matter, also abbreviated by ISM) and energy (interstellar radiation field, ISRF) content that exists http://space.wikia.com/wiki/Interstellar_medium

Wikia Skip to Content Skip to Wiki Navigation Skip to Site Navigation Wikia Navigation Start a wiki Entertainment Fall TV Glee ... Space Wiki Space Wiki Navigation Popular pages Most visited Newly changed Featured users ... Saturn Random Page Wiki Activity Watchlist Recent changes Talk Interstellar medium Edit Read more: Stars Astronomical objects Edited by Bryan Seecrets View full history The distribution of ionized hydrogen (known by astronomers as H II (aitch two) from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earth's northern hemisphere (from the Wisconsin H-Alpha Mapper Survey) Added by Bryan Seecrets In astronomy , the interstellar medium (or ISM ) is the matter interstellar matter , also abbreviated by ISM ) and energy interstellar radiation field ISRF ) content that exists between the stars within a galaxy . The ISM plays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales. Stars form within the densest regions of the ISM, molecular clouds, and replenish the ISM with matter and energy through planetary nebulae stellar winds , and supernovae . In turn, this interplay between stars and the ISM helps determine the rate at which a galaxy depletes its gaseous content, and therefore its lifespan of active star formation.

12. Interstellar Medium - On Opentopia, Find Out More About Interstellar Medium The distribution of ionized hydrogen (known by astronomers as H II (aitch two) from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the http://encycl.opentopia.com/term/Interstellar_medium

About Opentopia Opentopia Directory Encyclopedia ... Tools Interstellar medium Encyclopedia I IN INT : Interstellar medium The distribution of ionized hydrogen (known by astronomers as H II (aitch two) from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earth's northern hemisphere (from the Wisconsin H-Alpha Mapper Survey) In astronomy , the interstellar medium (or ISM ) is the matter interstellar matter , also abbreviated by ISM ) and energy interstellar radiation field ISRF ) content that exists between the star s within a galaxy . The ISM plays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales. Stars form within the densest regions of the ISM, molecular clouds, and replenish the ISM with matter and energy through planetary nebula e, stellar winds , and supernova e. In turn, this interplay between stars and the ISM helps determine the rate at which a galaxy depletes its gaseous content, and therefore its lifespan of active star formation. The ISM consists of an extremely dilute (by terrestrial standards) plasma gas and dust , consisting of a mixture of ion s

13. Interstellar Medium - Definition The interstellar medium (or ISM) is a term used in astronomy to describe the rarefied gas and dust that exists between the stars (or their immediate circumstellar environment http://www.wordiq.com/definition/Interstellar_medium

Interstellar medium - Definition The interstellar medium (or ISM ) is a term used in astronomy to describe the rarefied gas and dust that exists between the stars (or their immediate "circumstellar" environment) within a galaxy . The matter normally consists of about 99% gas particles and usually 1% of dust. This compound is usually extremely tenuous, with typical densities ranging from a few single to a few hundreds of a particles per cubic centimeter. Generally the gas is roughly 90% hydrogen and 10% helium, with additional elements (" metals " in astronomical parlance) present in trace amounts. The medium is also responsible for cosmic extinction , namely the decreasing light intensity of a star as the light travels through the medium. This extinction is caused by refraction and absorption of photons in certain wavelengths. For example, a typical absorption wavelength of atomic hydrogen lies at ca. 121.5 nm, the Lyman-alpha transition. Therefore, it is nearly impossible to see light emitted at that wavelength from a star, because most of it is absorbed during the trip to Earth by Lyman-alpha absorption. 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). This "three-phase" model of the ISM was initially developed by

14. Interstellar Medium Learning Pages About ISM from history of observation to current status of understanding. http://www-ssg.sr.unh.edu/ism/

Introduction Who What When ... Links Welcome, and thank you for visiting this tutorial! The pages are set up so that you can browse them in several different ways: by following the navigation links at left in the order that interests you; by following the links in a more linear fashion by using the and buttons at the bottom of each page; or by following the content links within the Introduction. Links relevant to each page will be showcased in the right-hand column; each of these will open in a new window. You can check definitions of unfamiliar words by holding your mouse cursor over highlighted words; clicking on the word will bring you to the Glossary. Use the "back" button in your browser to return to the page you were just looking at. Shields Up! The flow of interstellar helium in the solar system Coordinated observation of local interstellar Helium in the Heliosphere IBEX: Interstellar Boundary Explorer

15. Paul's Interstellar Medium Pages Interstellar medium. Paul P. van der Werf . Principal collaborators Miller Goss, Paul Vanden Bout, Lloyd Higgs, Peter Dewdney, Amiel Sternberg, J rgen Stutzki http://www.strw.leidenuniv.nl/~pvdwerf/research/ISM/

Interstellar medium Paul P. van der Werf Interstellar medium Overview Photon Dominated Regions HI near HII regions HI in molecular clouds Relevant links Research Overview Publications E-prints Curriculum vitae Navigation Leiden Observatory Home Last modified: Sun Mar 26 15:05:02 2006 Paul van der Werf Overview: The interstellar medium (ISM) of our Galaxy is key to understanding the lifecycle of stars and gas in the universe. Stars form from molecular clouds, but provide radiative and mechanical feedback on these clouds that makes the ISM a life, dynamical entity. The radiative feedback from massive stars on molecular clouds is observed directly in socalled Photon Dominated Regions (PDRs) , where the stellar ultraviolet (UV) radiation heats the ambient gas, affects its thermal balance and chemistry, and partly dissociates the H gas. The resulting atomic hydrogen (HI) can be observed directly as HI zones around HII regions . Molecular clouds without associated HII regions also contain atomic hydrogen, which is observed as HI in dark clouds Highlights: The Orion bar PDR: The Orion bar is a perfect example of an edge-on Photon Dominated Region or PDR , offering, at its distance of approximately 450 pc, excellent spatial resolution of its stratified structure. The bar is an edge-on ionization front at the South-East edge of the Orion Nebula (M42). The neutral gas outside the bar reveals a number of successive layers with increasing distance from the exciting stars (see image below). Closest to the ionization front, the emission of photo-excited polycyclic aromatic hydrocarbons (PAHs) peaks. Somewhat further from the ionization front, vibrationally excited H

16. What Is The Interstellar Medium? What is the Interstellar Medium? Simply put, the interstellar medium is the material which fills the space between the stars. Many people imagine outer space to be a complete http://www-ssg.sr.unh.edu/ism/what1.html

Introduction Who What When ... Links What is the Interstellar Medium? Simply put, the interstellar medium is the material which fills the space between the stars. Many people imagine outer space to be a complete vacuum, devoid of any material. Although the interstellar regions are more devoid of matter than any vacuum artificially created on earth, there is matter in space. These regions have very low densities and consist mainly of gas (99%) and dust . In total, approximately 15% of the visible matter in the Milky Way is composed of interstellar gas and dust. Interstellar Gas: Approximately 99% of the interstellar medium is composed of interstellar gas, and of its mass, about 75% is in the form of hydrogen (either molecular or atomic), with the remaining 25% as helium. The interstellar gas consists partly of neutral atoms and molecules , as well as charged particles, such as ions and electrons . This gas is extremely dilute, with an average density of about 1 atom per cubic centimeter. (For comparison, the air we breathe has a density of approximately 30,000,000,000,000,000,000 molecules per cubic centimeter.) Even though the interstellar gas is very dilute, the amount of matter adds up over the vast distances between the stars. The interstellar gas is typically found in two forms:

17. According To An Interstellar Medium... It looks as if our trusty ol' solar system is poised to enter a dense cloud of interstellar gas, an event that would change our atmosphere in unpredictable ways. http://whyfiles.org/017planet/gas_cloud2.html

It looks as if our trusty ol' solar system is poised to enter a "dense" cloud of interstellar gas, an event that would change our atmosphere in unpredictable ways. But not to worry it's not going to happen for several tens of thousands of years. Within about 50,000 years, the solar system could enter a much denser portion of the interstellar medium. How would that affect our atmosphere? Yellow arrow: sun's movement through space. White arrows: movement of gas cloud. Courtesy of Priscilla Frisch, the University of Chicago. Could the denser gas in "outer space" affect the atmosphere, and conditions on our planet? That's something that Priscilla Frisch, an astronomer at University of Chicago, wonders about. She notes that for the past 5 to 10 million years, Earth has occupied a region that's "virtually empty." When she says "virtually," she's serious : The interstellar medium now has about 0.1 hydrogen atom per cubic centimeter (and that's 1,000 times as dense as the last cloud). Astronomers don't bother comparing the density of the medium to that of liquid water, which weighs one gram per cubic centimeter (cc). Instead, they count the number of hydrogen atoms per cc. (For comparison, there are 700 billion billion hydrogen atoms in a cc of pure hydrogen gas at the pressure at Earth's surface). Frisch suggests that the vacuum-like interstellar medium may have promoted a stable atmosphere. "If the sun was being buffeted by a dense interstellar medium, it would probably affect our climate, although we don't know exactly how."

18. FusEdWeb | Fusion Education Part of a larger site on plasma physics. http://fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula.html

skip to: page content links on this page site navigation footer (site information) Bringing The Power Source of the Stars Down to Earth Home CPEP: Online Fusion Course Plasmas - the 4 th ... State of Matter CPEP: Online Fusion Course Main Topics Energy Sources and Conversions Two Key Fusion Reactions How Fusion Reactions Work Creating the Conditions for Fusion ... Achieving Fusion Conditions More Info About CPEP Fusion Chart Images: English + 6 More Languages Main CPEP Web Site Printed Charts in 3 Sizes Webby Awards Honoree April 10, 2007 Links Go - Fusion November 9, 1998 Overview The Guided Tour Planetary Nebulae A planetary nebula can result as a star with mass of less than several times the solar mass ("low mass" star) ejects mass in the red giant stage, near the end of the star's life. In this stage, the central part of the star, which is about the size of the earth, consists of a carbon ash core, a shell in which helium is fusing to carbon, and a shell where fusion of hydrogen to helium has temporarily ceased. The rest of the star's envelope has expanded to about 70 times larger than it had during most of its lifetime (almost the size of the orbit of Mars). The star at the center of the nebula is extremely hot, reaching temperatures of 200,000 K, emitting a large amount of the ultraviolet radiation which is necessary for ionization of hydrogen in the expanding gas. The resulting plasma is similar to that in the

19. The Interstellar Medium As we have noted above, the region between the stars in a galaxy like the Milky Way is far from empty. These regions have very low densities (they constitute a vacuum far http://csep10.phys.utk.edu/astr162/lect/milkyway/ism.html

The Interstellar Medium As we have noted above, the region between the stars in a galaxy like the Milky Way is far from empty. These regions have very low densities (they constitute a vacuum far better than can be produced artificially on the surface of the Earth), but are filled with gas, dust, magnetic fields, and charged particles. This is commonly termed the interstellar medium Approximately 99% of the mass of the interstellar medium is in the form of gas with the remainder primarily in dust. The total mass of the gas and dust in the interstellar medium is about 15% of the total mass of visible matter in the Milky Way. Gas in the Interstellar Medium Of the gas in the Milky Way, 90% by mass is hydrogen, with the remainder mostly helium. The gas appears primarily in two forms Cold clouds of atomic or molecular hydrogen Hot ionized hydrogen near hot young stars The clouds of cold molecular and atomic hydrogen represent the raw material from which stars can be formed in the disk of the galaxy if they become gravitationally unstable and collapse. Although such clouds do not emit visible radiation, they can be detected by their radio frequency emission. HI and HII Regions Ionized hydrogen is produced when the ultraviolet radiation emitted copiously by hot newly-formed stars ionizes surrounding clouds of gas. The characteristic beautiful red colors of emission nebulae like the

20. Interstellar Medium interstellar medium, region between the stars that contains vast, diffuse clouds of gases and minute solid particles. Such tenuous matter in the interstellar medium of the Milky http://www.uv.es/EBRIT/micro/micro_292_92.html

Britannica CD Index Articles Dictionary Help interstellar medium, region between the stars that contains vast, diffuse clouds of gases and minute solid particles. Such tenuous matter in the interstellar medium of the Milky Way system, in which the Earth is located, accounts for about 5 percent of the Galaxy's total mass. A brief treatment of the interstellar medium follows. For full treatment, see MACROPAEDIA: Galaxies The interstellar medium is filled primarily with hydrogen gas. A relatively significant amount of helium has also been detected, along with smaller percentages of such substances as calcium, sodium, water, ammonia, and formaldehyde. Sizable quantities of dust particles of uncertain composition are present as well. In addition, primary cosmic rays travel through interstellar space, and magnetic fields thread their way across much of the region. In most cases, interstellar matter occurs in cloudlike concentrations, which sometimes condense enough to form stars. These stars, in turn, continually lose mass, in some instances through small eruptions and in others in catastrophic explosions known as supernovae. The mass is thus fed back to the interstellar medium, where it mixes with matter that has not yet formed stars. This circulation of interstellar matter through stars determines to a large degree the amount of heavier elements in the cosmic clouds. Interstellar matter in the Milky Way Galaxy is found primarily in the system's outer parts ( i.e.

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