1. The Local Interstellar Medium 3D Mapping of the Local interstellar medium. Outline. http://spacsun.rice.edu/~twg/lism.html

3-D Mapping of the Local Interstellar Medium Outline Introduction: the Local Interstellar Medium Overall Picture Opacity of the ISM Ultraviolet Probing of the ISM ... References Introduction By the "Local Interstellar Medium (LISM)", we mean the gas occupying the space between the stars out to a distance of a couple of hundred parsecs from the Sun. We now know that the density and temperature of this gas varies greatly from place to place and with data from orbiting observatories, we are now able to form a general picture of how the gas is distributed. ROSAT is a satellite bearing telescopes which can observe the X-ray and EUV (Extreme Ultraviolet) radiation from stars and other objects in space. ROSAT observations of certain types of stars can be used to probe the structure of the LISM, as described below. Return to Outline Overall Picture of the LISM The images below are "artist's impressions" of how our galaxy would look if we could see the hydrogen gas in between the stars, as well as the stars themselves. Some of the data upon which these paintings are based is presented in the last section of this document. Click on the image to see it enlarged and described. The number above each image gives the approximate size of the region in parsecs (1 pc = 3.26 light-years). 25,000 pc

2. Astronomy HyperText Book: Interstellar Medium Much Still Under Development The interstellar medium (ISM) is the stuff between the stars. Most of this stuff consists of gas and dust . http://zebu.uoregon.edu/textbook/ism.html

Much Still Under Development The Interstellar Medium (ISM) is the stuff between the stars. Most of this stuff consists of gas and dust . The gas content of the ISM continually decreases with time as new generations of stars form from the collapse of giant molecular clouds. The collapse and fragementation of these clouds give rise to the formation of stellar clusters . Since the mass function of star formation strongly favors the formation of low mass stars, then each new star formation locks up available ISM gas into a reservoir of unevolving low mass stars. Click here for a schematic representation of the form of the mass function. The dust particles are sufficiently small that they scatter short wavelength light more efficiently than long wavelength light. In fact, blue photons are scattered about 10 times more efficiently than red photons. Basic Principle of Photon Scattering Audio Narration is available No Scattering: Photon Source and Detector Audio Narration is available For optical photons, scattering goes as wavelength to the -4 power. In the case of blue photons compared to red photons, this means that blue photons are about 10 times more likely to get scattered than red photons. This is shown in the next animation. Watch the blue photons scatter away from the detector Audio Narration is available Here we see that only the red photon survives the scattering network to reach the detector Interstellar dust make stars appear redder than they really are Audio Narration is available

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

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: Cold clouds of neutral atomic or molecular hydrogen; and

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

Although the subject may sound INTIMIDATING... It does not have to be. Begin here with the basics: After you have learned the basics, move on to...

5. The Interstellar Medium And Intergalactic MediumThe Interstellar Medium And Inte   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 http://www.gsu.edu/other/timeline/ether.html

The Interstellar Medium and Intergalactic Medium 1848 : Lord Rosse studies M1 and names it the Crab Nebula 1864 : William Huggins studies the spectrum of the Orion Nebula and shows that it is a cloud of gas 1927 : Ira Bowen explains unidentified spectral lines from space as forbidden transition lines 1930 : Robert Trumpler discovers absorption by interstellar dust by comparing the angular sizes and brightnesses of globular clusters 1944 : Hendrik van de Hulst predicts the 21 cm hyperfine line of neutral interstellar hydrogen 1951 : H.I. Ewen and Edward Purcell observe the 21 cm hyperfine line of neutral interstellar hydrogen 1956 : Lyman Spitzer predicts coronal gas around the Milky Way 1965 : James Gunn and Bruce Peterson use observations of the relatively low absorption of the blue component of the Lyman-alpha line : from 3C9 to strongly constrain the density and ionization state of the intergalactic medium 1969 : Lewis Snyder, David Buhl, Ben Zuckerman, and Patrick Palmer find interstellar formaldehyde 1970 : Arno Penzias and Robert Wilson find interstellar carbon monoxide 1970 : George Carruthers observes molecular hydrogen in space 1977 : Christopher McKee and Jeremiah Ostriker propose a three component theory of the interstellar medium Return to Timeline Index Text by niel@cast0.ast.cam.ac.uk

6. ADC Quick Reference: Interstellar Medium (ISM) ADC Quick Reference Page interstellar medium (ISM). in our GALAXY http://adc.gsfc.nasa.gov/adc/quick_ref/ref_ism.html

Astronomical Data Center ADC Quick Reference Page: INTERSTELLAR MEDIUM (ISM) in our GALAXY How to use this Page This page contains links to data pertaining to the following subjects: Interstellar Dust Diffuse H I Warm Ionized Medium (WIM) Hot Ionized Medium (HIM) ... Cosmic Rays Find the topic of interest to you and click on any of the references listed. References listed on a yellow background are ADC holdings, and the hyperlink will transfer you to the ADC documentation on that reference, and give you the option of pre-viewing the data product using the ADC Viewer software, or downloading the product through FTP. Also included on this page are links to selected external (non-ADC) resources which may be of interest. These are labelled as 'External links' or 'Additional Websites'. The ADC is not responsible for the content of external sites linked from this page. This quick reference page is designed to point the user toward some of the more frequently used ADC dataset holdings regarding the interstellar medium (ISM). The references listed here constitute only a small fraction of the total references available; if you do not see a topic or reference covered here, you may perform a search of the complete ADC holdings: [Search ADC Archives] INTERSTELLAR DUST Extinction/Reddening 2088B uvby-Beta Data for Local Interstellar Reddening Map (Perry+ 1982) 2062 Catalogue of Extinction Data (Neckel+ 1980) 2114 UV Interstellar Extinction Excesses for 1415 Stars (Savage+ 1985) 2175 Catalogue of 166 Ultraviolet Extinction Curves (Krelowski+ 1992) ... J/A+A/275/549 Environ. dependence of interstellar extinction (Jenniskens+ 1993)

7. Interstellar Medium This set of notes by Nick Strobel covers the interstellar mediumthe effect of dust, emission nebulae, 21 cm radiation, http://www.maa.mhn.de/Scholar/interstmat.html

Interstellar Medium This set of notes by Nick Strobel covers: the interstellar mediumthe effect of dust, emission nebulae, 21 cm radiation, mapping galactic structure, and molecules.These notes will be in outline form to aid in distinguishing various concepts. As a way to condense the text down I'll often use phrases instead of complete sentences. The vocabulary terms are italicized. Contents Interstellar Medium (ISM) Dust Extinction Reddening ... Molecules Molecular clouds Photo Gallery of Nebulae (Under construction) Interstellar Medium (ISM) Index Stuff between the stars. 10-15% of the visible mass of the Galaxy. 99% of the ISM mass is gas; 1% dust. ``So what?'' Why do we worry about the interstellar medium? The interstellar medium affects starlight and stars are formed from ISM! A. Dust Dust -about the size of the wavelength blue light or smaller. Water ice, graphite (Carbon), Silicon in highly flattened flakes or needles. Effects of dust on light: Extinction Extinction dimming of starlight at all wavelengths. In 1930 R.J. Trumpler plots angular diameter of clusters vs. distance to cluster. Distance found from inverse square law of brightness. IF clusters all have nearly same linear diameter s , then the angular diameter should equal a constant size / distance ( theta = s/D ). But he found a

8. Astronomy Supplement - The Interstellar Medium Although stars interact with the interstellar medium over the course of their entire lives, we want to divided that http://www.physics.gmu.edu/classinfo/astr103/CourseNotes/ECText/ch16_txt.htm

Astronomy Supplement 16. The Interstellar Medium Latest Modification: October 26, 1998 Table of Contents 16.1. Mass Loss by the Sun and Stars 16.1.1. The Solar Wind 16.1.2. Mass Loss by Stellar Winds 16.2. Explosive Variable Stars 16.2.1. Planetary Nebulae 16.2.2. Novae 16.2.3. Supernovae Box 16.1. - The Crab Nebula and Pulsar 16.3. Interstellar Matter 16.3.1. Interstellar Gas 16.3.2. The 21-CM Line Biography - Karl Guthe Jansky (1905-1950) 16.3.3. Interstellar Molecules 16.3.4. Interstellar Dust 16.4. Interstellar Clouds 16.4.1. Diffuse and Dark Clouds 16.4.2. Obscuring Effect of Interstellar Clouds 16.4.3. Carbon Monoxide in Dark Clouds 16.4.4. Interstellar Masers, Dark Clouds with Energy Sources 16.5. Emission Nebulae 16.5.1. H II Regions 16.5.2. What Type of Interstellar Medium Surrounds the Sun? If you exhale your breath once and let it expand into an evacuated cubical enclosure 1 kilometer on a side, the resulting density of your breath will exceed the density in most parts of the interstellar medium. Although this suggests that interstellar space is nearly a vacuum, there is a significant amount of matter lying between the stars because of the vast volume of space. Interstellar matter is primarily a gas, in which hydrogen is the chief component. In regions near very luminous, hot stars the gas is ionized, whereas in other regions it is so cold that molecules exist in it. Thus the interstellar medium is far from uniform in its properties. Mixed with the interstellar gas is a very fine dust, whose grains are about the size of the particles that are seen as small flashes in a shaft of light coming through a window. Interstellar dust, however, has a very different chemical composition and origin than particles of Earth dust.

9. Interstellar Medium Learning Pages After you have learned the basics, move on to The interstellar medium In Depth. http://www-ssg.sr.unh.edu/tof/Outreach/Interstellar/?what1.html

10. University Of Massachusetts - High Energy Astrophysics Group Research group primarily interested in high energy activities in galaxies, particularly the interplay between massive stars and the interstellar medium. http://www.astro.umass.edu/ast_page/xray/heag.html

11. MOST Canada's First Space Telescope --- MOST Project UBC Homepage Detection and characterisation of (1) acoustic oscillations in Sunlike stars, including very old stars (metal-poor subdwarfs) and magnetic stars (roAp), to probe seismically their structures and ages; (2) reflected light from giant exoplanets closely orbiting Sun-like stars, to reveal their sizes and atmospheric compositions; and (3) turbulent variations in massive evolved (Wolf-Rayet) stars to understand how they add gas to the interstellar medium. http://www.astro.ubc.ca/MOST/

The graphic embeded here is a Shockwave Animation and hence requires the according plugin to be displayed properly.

12. The Astronomical Journal Founded in 1849 and published by the American Astronomical Society with an emphasis on observational papers. Its expanded coverage of quasars, galaxies, supernova remnants, and studies of the interstellar medium complements the more traditional areas of astronomy, including galactic structure and dynamics, astrometry, variable and binary stars, solar system studies, and cosmology. http://www.journals.uchicago.edu/AJ/home.html

Editor: Paul Hodge Sponsor: American Astronomical Society ISSN: 0004-6256 The Astronomical Journal Electronic Edition Editorial Office Home Page, Seattle Journal Description Information about Electronic Subscriptions List of Institutions Currently Registered Letter to Institutional Subscribers Registration Form Institutional Site License ... Letter, Registration Form, and Site License (PDF) Editorial Board Information for Authors General Instructions to Authors Electronic Submission Guidelines Key Words IAU Recommendations for Nomenclature ... Page Charge Authorization Form (PDF) Publication Agreement Form (PDF) Preparation of Word and WordPerfect Manuscripts General Instructions Special Instructions for Tables Special Instructions for Math How to Subscribe to ... AJ Order Single Articles or Back Issues AAS Centennial Volume (PDF) Review Of Related Interest from the University of Chicago Press Contact the Editorial Office Subscription Center ... Journals Division

13. Interstellar Medium: Cold interstellar medium When one Neutral Hydrogen Most of the interstellarmedium is in the form of neutral hydrogen gas (HI). The typical http://zebu.uoregon.edu/~js/ast122/lectures/lec18.html

Interstellar Medium When one looks up into the night sky we only see stars and the occasional planet. Most of outer space is empty, meaning that the density of atoms is much lower than even the best vacuums in our labs. Deep imaging of the skies showed that there are numerous regions where interstellar matter, in the form of gas and dust, collects to form clouds and nebula. Since these clouds are diffuse, they are difficult to see with the naked eye. The first indication that there was interstellar gas and dust was dark lanes in the Milky Way. Since we live in a disk galaxy, then looking outward we see a band of light in the sky which, if magnified, breaks down into the many stars in our Galaxy. A deep photo of the Milky Way shows that there are dark regions or lanes. We understand now that there is gas and dust blocking the starlight which produces these dark lanes, such as the CoalSack Nebula . In fact, most of our Galaxy is blocked from our view by patches of gas and dust Interstellar Extinction Astrophotography in the 19th century showed that the dark lanes or holes in the Milky Way did not have sharp edges. That, in fact, detail studies of star clusters at various distances from us showed that the intensity of light from remote stars is reduced as it passes through the sparse material of the interstellar medium. Herschel tried to use star counts to measure the size of the Galaxy and where our position is within it. His result was the diagram below, but what he really discovered was that interstellar extinction limits our line of sight.

14. Sterrewacht Leiden | Leiden Observatory - Welcome Research focuses on a number of different areas covering astronomical interests which range from the study of stars and the interstellar medium to galaxies and the largescale structure of the universe. http://www.strw.leidenuniv.nl/

Home Search eval(unescape('%64%6f%63%75%6d%65%6e%74%2e%77%72%69%74%65%28%27%3c%61%20%68%72%65%66%3d%6d%61%69%6c%74%6f%3a%77%65%62%6d%61%73%74%65%72%40%73%74%72%77%2e%6c%65%69%64%65%6e%75%6e%69%76%2e%6e%6c%20%63%6c%61%73%73%3d%22%6e%61%76%62%61%72%22%3e%43%6f%6e%74%61%63%74%3c%2f%61%3e%27%29')) Contact Welcome Research Education About Outreach ... American Ambassador in Leiden About Leiden Observatory -General information -Addresses -Staff and organization -Facilities ... On the Occasion of the Retirement of H.J. Habing (April 10-11) Fourteenth Oort Lecture, Prof. A. Dalgarno (April 24) Nederlandse Astronomen Conferentie (21 - 23 mei) Zomerschool Astrofysica 2003 Education -Sterrenkunde studeren in Leiden -Education in astronomy at Leiden University ... -J. Mayo Greenberg Scholarship Prize Astronomical links -Worldwide -The Netherlands -Astronomical software -International Astronomical Union ... -Starlink e-mail addresses Startingpoints on the Web -Leiden -The Netherlands -Worldwide

15. The Interstellar Medium Gas in the interstellar medium. Of the gas in the Milky Way, 90% by mass is hydrogen,with the remainder mostly helium. Dust in the interstellar medium. 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

16. The Interstellar Medium (ISM) The interstellar medium (ISM). The interstellar medium represents theraw material for forming future generations of stars. Nebulae. http://pegasus.phast.umass.edu/a100/handouts/ism.html

The Interstellar Medium (ISM) Gas and Dust between the stars accounts for 2030% of the mass of our Galaxy. Much of this material has been ejected by old and dying stars 99% of the ISM is gas mostly Hydrogen about one atom per cubic centimeter 1% is in microscopic (about 1 micron diameter) dust grains. Composition: silicates, carbon, or ice about one grain per cubic football field The interstellar medium represents the raw material for forming future generations of stars. Nebulae The distribution of the ISM is ``clumpy". Dark Clouds Dust blocks distant stars from view. Reflection Nebulae Nearby stars illuminate a dust cloud. Emission Nebulae (HII regions) Hot nearby stars ionize gas causing it to glow. Most of the light comes from the discrete spectral lines of the elements. Created March 28, 1996

17. Lecture: Interstellar Medium Astronomy 124. The interstellar medium. This material is collectivelyknown as the interstellar medium the material between the stars. http://www.astro.virginia.edu/class/hawley/astr124/ism.html

Astronomy 124 The Interstellar Medium Before we begin our extensive discussion regarding the evolution of stars, we must start with a discussion of the stuff out of which stars are made, namely the gas and dust that is present throughout the galaxy. This material is collectively known as the interstellar medium : the material between the stars. One tends to think of outer space as consisting solely of stars separated by great distances with a complete vacuum between them. While it is true that space is mostly empty, there are regions that contain considerable material. This is relative of course. By earthly standards such regions still constitute a pretty good vacuum. For example, the "typical" gas density in space is one atom per cubic centimeter. The best man-made vacuum is about 10 atoms per cubic centimeter. A cc of the air in the room has about 10 atoms in it. The interstellar medium is not uniform in density. Although on average its density is one atom per cc, it can have densities up to a thousand or a million atoms per cc. The interstellar medium is composed of two classes of material: gas and dust . Gas is composed of molecules or atoms of types of gasses, hydrogen being the most abundant. Carbon monoxide, CO, is another common form of gas, as are oxygen and nitrogen. Dust is composed of little bits of solid matter. Dust is very small, on the order of microns (10

18. Interstellar Medium And The Milky Way interstellar medium and the Milky Way. Full window version (looks a littlenicer). The vocabulary terms are in boldface. interstellar medium (ISM). http://www.maa.mhn.de/Scholar/Interstmat/ismglxya.html

This page was copied from Nick Strobel's Astronomy Notes . Go to his site at www.astronomynotes.com for the updated and corrected version. Interstellar Medium and the Milky Way Full window version This material (including line art and animations) is See my for fair use practices. Most of the ground-based telescope pictures here are from the Anglo-Australian Observatory (AAO-used by permission). Our solar system is inside a large galaxy known as the Milky Way . All of the stars you can see at night and several hundred billion more are all bound together gravitationally into a huge cluster called a galaxy . Most of the stars in our galaxy are far enough away that they blend together in a thin band across the sky. If you are fortunate enough to view a dark sky outside of the glare of the city lights, you will see this milky band running through the constellations Cassiopeia, Perseus, Taurus, Monoceros, Vela, Crux, Norma, Sagittarius, Scutum, Aguila, Cygnus, and Lacerta. To people of long ago, this band looked like milk had been spilled along a pathway, so it was called the Milky Way. This chapter covers the radical discoveries made in the 20th century of the nature of the Milky Way and our place in it. The vocabulary terms are in boldface Interstellar Medium (ISM) Though the space between the stars is emptier than the best vacuums created on the Earth (those are enclosed spaces devoid of matter, not the household cleaning appliances), there is some material between the stars composed of gas and dust. This material is called the

19. The Interstellar Medium University of California, San Diego Center for Astrophysics SpaceSciences. Gene Smith's Astronomy Tutorial The interstellar medium, http://casswww.ucsd.edu/public/tutorial/ISM.html

University of California, San Diego Gene Smith's Astronomy Tutorial The Interstellar Medium Although space is very empty and the stars in the Milky Way are very far apart, the space between the stars contains a very diffuse medium of gas and dust astronomers call the interstellar medium (ISM) . This medium consists of neutral hydrogen gas (HI), molecular gas (mostly H ), ionized gas (HII), and dust grains. Although the interstellar medium is, by several orders of magnitude, a better vacuum than any physicists can create in the laboratory there is still about of 5-10 billion M of gas and dust out there, comprising approximately 5% of the mass of visible stars in the Galaxy. Neutral Hydrogen Gas The Milky Way Galaxy is filled with a very diffuse distribution of neutral hydrogen gas which has a typical density of about 1 atom/cm g/cm ). The interstellar medium is far too cool to excite the UV or optical transitions of hydrogen, but there is a feature at 21 cm wavelength in the radio produced by the spins (magnetic fields) of the hydrogen atom's nuclear proton and orbiting electron. Because the proton and electron are spinning distributions of electric charge they create minute magnetic fields which interact, creating a small energy difference between the state in which the poles are aligned versus counter-aligned. This energy difference corresponds to the energy of radio waves at 21-centimeters. Every once in a while (about once per 500 years) hydrogen atoms will collide, exciting an atom into the higher energy spin-aligned configuration. It will take as long as 30 million years for the atom to jump back to the lower energy state via a

20. Physics 7 Lecture #13(Cont'd) - The Interstellar Medium Diego Physics 7 Introduction to Astronomy. HE Smith, Winter 2001.Physics 7 - Lecture Summary 13 (Continued) The interstellar medium, http://casswww.ucsd.edu/physics/ph7/ISM.html

University of California, San Diego Physics 7 - Introduction to Astronomy H. E. Smith Winter 2001 Physics 7 - Lecture Summary #13 (Continued) The Interstellar Medium Although space is very empty and the stars in the Milky Way are very far apart, the space between the stars contains a very diffuse medium of gas and dust astronomers call the interstellar medium (ISM) . This medium consists of neutral hydrogen gas (HI), molecular gas (mostly H ), ionized gas (HII), and dust grains. Although the interstellar medium is, by several orders of magnitude, a better vacuum than any physicists can create in the laboratory there is still about of 5-10 billion M of gas and dust out there, comprising approximately 5% of the mass of visible stars in the Galaxy. Neutral Hydrogen Gas The Milky Way Galaxy is filled with a very diffuse distribution of neutral hydrogen gas which has a typical density of about 1 atom/cm g/cm ). The interstellar medium is far too cool to excite the UV or optical transitions of hydrogen, but there is a feature at 21 cm wavelength in the radio produced by the spins (magnetic fields) of the hydrogen atom's nuclear proton and orbiting electron. Because the proton and electron are spinning distributions of electric charge they create minute magnetic fields which interact, creating a small energy difference between the state in which the poles are aligned versus counter-aligned. This energy difference corresponds to the energy of radio waves at 21-centimeters. Every once in a while (about once per 500 years) hydrogen atoms will collide, exciting an atom into the higher energy spin-aligned configuration. It will take as long as 30 million years for the atom to jump back to the lower energy state via a

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