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 northern hemisphere as observed with the Wisconsin Hα Mapper (Haffner et al. 2003). In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound

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. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study This page is about the physical properties of gas as a state of matter Matter is commonly defined as being anything that has mass and that takes up space. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter It fills interstellar space and blends smoothly into the surrounding intergalactic medium. Intergalactic space is the physical space between galaxies. Generally free of dust and debris intergalactic space is very close to a total Vacuum. The energy, in the form of electromagnetic radiation, that occupies the same volume is the interstellar radiation field. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter.

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 (Spitzer 1978). An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on The matter consists of about 99% gas and 1% dust by mass. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Densities range from a few thousand to a few hundred million particles per cubic meter with an average value in the Milky Way Galaxy of a million particles per cubic meter. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different CM3 redirects here If you were looking for the 3rd game in the Cooking Mama series abbreviated as CM3 see here. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply As a result of primordial nucleosynthesis, the gas is roughly 90% hydrogen and 10% helium by number of nuclei, with additional heavier elements ("metals" in astronomical parlance) present in trace amounts. In Physical cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than those of H-1 (i Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. In Astronomy and Physical cosmology, the metallicity of an object is the proportion of its matter made up of Chemical elements other than Hydrogen

The ISM plays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales. Astrophysics is the branch of Astronomy that deals with the Physics of the Universe, including the physical properties ( Luminosity, 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. See also Solar nebula A molecular cloud, sometimes called a stellar nursery if Star formation is occurring within is a type of Interstellar A planetary nebula is an Emission nebula consisting of a glowing shell of Gas and plasma formed by certain types of Stars when they die The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. A supernova (plural supernovae or supernovas) is a stellar Explosion. 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 history of knowledge of interstellar space

The nature of the interstellar medium has received the attention of astronomers and scientists over the centuries. However, they first had to acknowledge the basic concept of "interstellar" space. The term appears to have been first used in print by Bacon (1626, § 354–5): "The Interstellar Skie. . hath . . so much Affinity with the Starre, that there is a Rotation of that, as well as of the Starre. " Later, natural philosopher Robert Boyle (1674) discussed "The inter-stellar part of heaven, which several of the modern Epicureans would have to be empty. For the current in the 19th century German idealism see Naturphilosophie Natural philosophy or the philosophy of nature (from Robert Boyle was a Natural philosopher, chemist physicist inventor and early Gentleman scientist, noted for his work in Physics and Chemistry "

Before modern electromagnetic theory early physicists postulated that an invisible luminiferous aether existed as a medium to carry lightwaves. A physicist is a Scientist who studies or practices Physics. Physicists study a wide range of physical phenomena in many branches of physics spanning In the late 19th century " luminiferous aether " (or " ether " meaning light-bearing aether, was the term used to describe a medium for the propagation It was assumed that this aether extended into interstellar space, as Patterson (1862) wrote, "this efflux occasions a thrill, or vibratory motion, in the ether which fills the interstellar spaces. "

The advent of deep photographic imaging allowed Edward Barnard to produce the first images of dark nebulae silhouetted against the background star field of the galaxy while the first actual detection of cold diffuse matter in interstellar space was made by Johannes Hartmann in 1904 through the use of absorption line spectroscopy. Edward Emerson Barnard ( December 16, 1857 – February 6, 1923) was an American Astronomer. A dark nebula is a type of Interstellar cloud that is so dense that it obscures the light from the background emission or Reflection nebula (e Johannes Franz Hartmann ( January 11, 1865 – September 13, 1936) was a German Physicist and Astronomer. A material's absorption spectrum shows the fraction of incident Electromagnetic radiation absorbed by the material over a range of Frequencies. In this historic study of the spectrum and orbit of Delta Orionis, Hartmann observed the light coming from this star and realized that some of this light was being absorbed before it reached the Earth. Delta Orionis (δ Ori traditionally known as Mintaka (from منطقة manţaqah, which means "belt" in Arabic), is a Star some 900 Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 Hartmann reported that absorption from the "K" line of calcium appeared "extraordinarily weak, but almost perfectly sharp" and also reported the "quite surprising result that the calcium line at 393. Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 4 nanometres does not share in the periodic displacements of the lines caused by the orbital motion of the spectroscopic binary star". A binary star is a Star system consisting of two Stars orbiting around their Center of mass. The stationary nature of the line led Hartmann to conclude that the gas responsible for the absorption was not present in the atmosphere of Delta Orionis, but was instead located within an isolated cloud of matter residing somewhere along the line-of-sight to this star. This discovery launched the study of the ISM.

Following the identification of interstellar calcium absorption by Hartmann, interstellar sodium was detected by Heger (1919) through the observation of stationary absorption from the atom's "D" lines at 589. Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 0 and 589. 6 nanometres towards Delta Orionis and Beta Sco. Beta Scorpii (β Sco / β Scorpii is a Star system in the Constellation Scorpius.

Subsequent observations of the "H" and "K" lines of calcium by Beals (1936) revealed double and asymmetric profiles in the spectra of Epsilon and Zeta Orionis. Alnilam is a large blue Star in the Constellation of Orion. It also has the modern name Epsilon Orionis (ε Ori / ε Orionis Zeta Orionis (ζ Ori traditionally known as Alnitak ( Arabic: النطاق an-niṭāq) is a triple star some 800 light years distant in the These were the first steps in the study of the very complex interstellar sightline towards Orion. Orion (ɒˈraɪən a Constellation often referred to as The Hunter, is a prominent constellation one of the largest and perhaps the best-known and most conspicuous Asymmetric absorption line profiles are the result of the superposition of multiple absorption lines, each corresponding to the same atomic transition (for example the "K" line of calcium), but occurring in interstellar clouds with different radial velocities. Radial velocity is the Velocity of an object in the direction of the line of sight (i Because each cloud has a different velocity (either towards or away from the observer/Earth) the absorption lines occurring within each cloud is either Blue-shifted or Red-shifted (respectively) from the lines rest wavelength through the Doppler Effect. Blue shift is the shortening of a transmitted signal's Wavelength, and/or an increase in its Frequency, due to the Doppler Effect, which indicates that In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by The Doppler effect (or Doppler shift) named after Christian Doppler, is the change in Frequency and Wavelength of a Wave for These observations highlight that matter is not distributed homogeneously and were the first evidence for the presence of multiple discrete clouds within the ISM.

The growing evidence for interstellar material led Pickering (1912) to comment that "While the interstellar absorbing medium may be simply the ether, yet the character of its selective absorption, as indicated by Kapteyn, is characteristic of a gas, and free gaseous molecules are certainly there, since they are probably constantly being expelled by the Sun and stars. Jacobus Cornelius Kapteyn, ( January 19, 1851 &ndash June 18, 1922) was a Dutch astronomer, best known for his extensive "

The same year Victor Hess's discovery of cosmic rays, highly energetic charged particles that rain down on the Earth from space, led others to speculate whether they also pervaded interstellar space. Victor Francis Hess ( June 24, 1883 &ndash December 17, 1964) was an Austrian American Physicist, and For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The following year the Norwegian explorer and physicist Kristian Birkeland wrote: "It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. Kristian Olaf Birkeland ( December 13, 1867 - June 15, 1917) was born in Christiania ( Oslo today and wrote his first We have assumed that each stellar system in evolutions throws off electric corpuscles into space. It does not seem unreasonable therefore to think that the greater part of the material masses in the universe is found, not in the solar [sic] systems or nebulae, but in 'empty' space" (Birkeland 1913).

Thorndike (1930) noted that "it could scarcely have been believed that the enormous gaps between the stars are completely void. Terrestrial aurorae are not improbably excited by charged particles from the Sun emitted by the Sun. If the millions of other stars are also ejecting ions, as is undoubtedly true, no absolute vacuum can exist within the galaxy. "

Interstellar matter

The three-phase model

Field, Goldsmith & Habing (1969) put forward the static two phase equilibrium model to explain the observed properties of the ISM. Their ISM consisted of a cold dense phase (T < 300 K), consisting of clouds of neutral and molecular hydrogen, and a warm intercloud phase (T ~ 10⁴ K), consisting of rarefied neutral and ionized gas. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic McKee & Ostriker (1977) added a dynamic third phase that represented the very hot (T ~ 10⁶ K) gas which had been shock heated by supernovae and constituted most of the volume of the ISM. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Their paper formed the basis for further study over the past three decades. However, the relative proportions of the phases and their subdivisions are still not well known (Ferriere 2001).

Table 1 shows a breakdown of the properties and origin of the components of the three phases.

Structures

The ISM is turbulent, and therefore full of structure on all spatial scales. In Physics and Astronomy, H-alpha, also written Hα, is a specific Emission line created by Hydrogen at 6562 Pulsars are highly magnetized rotating Neutron stars that emit a beam of Electromagnetic radiation in the form of radio waves An H II region (also known as Emission nebula) is a cloud of glowing Gas and plasma, sometimes several hundred Light-years across In Physics and Astronomy, H-alpha, also written Hα, is a specific Emission line created by Hydrogen at 6562 Pulsars are highly magnetized rotating Neutron stars that emit a beam of Electromagnetic radiation in the form of radio waves A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily X-ray astronomy is an observational branch of Astronomy, which deals with the study of X-ray emission from celestial objects Ultraviolet astronomy is generally used to refer to observations at Ultraviolet wavelengths between approximately 10 and 320 nanometres

Stars are born deep inside large complexes of molecular clouds, typically a few parsecs in size. Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. See also Solar nebula A molecular cloud, sometimes called a stellar nursery if Star formation is occurring within is a type of Interstellar History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 During their lives and deaths, stars interact with the ISM physically.

Stellar winds from young clusters of stars (often with giant or supergiant HII regions surrounding them) and shock waves created by supernovae inject enormous amounts of energy into their surroundings, which leads to hypersonic turbulence. A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a Star. An H II region (also known as Emission nebula) is a cloud of glowing Gas and plasma, sometimes several hundred Light-years across For the music album by Converter see Shock Front For the 1977 horror film see Shock Waves A shock wave (also called A supernova (plural supernovae or supernovas) is a stellar Explosion. The resultant structures – of varying sizes – can be observed, such as bubbles and superbubbles of hot gas seen by X-ray satellite telescopes or turbulent flows observed in radio telescope maps. Stellar wind bubble is the astronomical term usually used to describe a cavity light years across filled with hot gas blown into the Interstellar medium by the high-velocity Superbubble is the astronomical term used to describe a cavity hundreds of light years across filled with 106  K gas blown into the Interstellar A radio telescope is a form of directional Radio antenna used in Radio astronomy and in tracking and collecting data from Satellites

The Sun is currently traveling through the Local Interstellar Cloud, a denser region in the low-density Local Bubble. The Local Interstellar Cloud, casually called the Local Fluff, is the Interstellar cloud (roughly 30 light years across through which our Solar system The Local Bubble is a cavity in the Interstellar medium (ISM of the Orion Arm of the Milky Way.

Interaction with interplanetary medium

Schematic diagram of the interaction between the ISM and the interplanetary medium.

The interstellar medium begins where the interplanetary medium of the Solar System ends. The interplanetary medium is the material which fills the solar system and through which all the larger solar system bodies such as Planets Asteroids The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The solar wind slows to subsonic velocities at the termination shock, 90—100 astronomical units from the Sun. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the The Sun (Sol is the Star at the center of the Solar System. In the region beyond the termination shock, called the heliosheath, interstellar matter interacts with the solar wind. The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the Voyager 1, the furthest human-made object from the Earth, crossed the termination shock on 2004-12-16 and may eventually enter interstellar space, providing the first direct probe of conditions in the ISM (Stone et al. 2005). The Voyager 1 spacecraft is a 722-kilogram robotic Space probe of the outer Solar system and beyond launched September 5, "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Events 755 - An Lushan revolts against Chancellor Yang Guozhong at Fanyang, initiating the An Shi Rebellion

Interstellar extinction

The ISM is also responsible for extinction and reddening, the decreasing light intensity and shift in the dominant observable wavelengths of light from a star. Extinction is a term used in Astronomy to describe the absorption and Scattering of Electromagnetic radiation emitted by Astronomical objects In Astronomy, interstellar reddening is a phenomenon associated with interstellar extinction where the spectrum of Electromagnetic radiation In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. These effects are caused by scattering and absorption of photons and allows the ISM to be observed with the naked eye in a dark sky. The rifts that can be seen in the band of the Milky Way are caused by absorption of background starlight from the uniform disk of stars by molecular clouds within a few thousand light years.

Far ultraviolet light is absorbed effectively by the neutral components of the ISM. For example, a typical absorption wavelength of atomic hydrogen lies at about 121. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 5 nanometers, the Lyman-alpha transition. In Physics, the Lyman series is the series of transitions and resulting Emission lines of the Hydrogen Atom as an Electron goes from Therefore, it is nearly impossible to see light emitted at that wavelength from a star farther than a few hundred light years from Earth, because most of it is absorbed during the trip to Earth by intervening neutral hydrogen. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001

Heating of the interstellar medium

The ISM is usually far out of thermodynamic equilibrium. In Thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium Mechanical equilibrium, and Collisions establish a Maxwell-Boltzmann distribution of velocities, and the 'temperature' normally used to describe interstellar gas is the 'kinetic temperature', which describes the temperature at which the particles would have the observed Maxwell-Boltzman velocity distribution in thermodynamic equilibrium. The Maxwell–Boltzmann distribution is a Probability distribution with applications in Physics and Chemistry. However, the interstellar radiation field is typically much weaker than in thermodynamic equilibrium; it is most often roughly that of an A star (surface temperature of ~10,000 K) highly diluted. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics Therefore, bound levels within an atom or molecule in the ISM are rarely populated according to the Boltzmann formula (Spitzer 1978 S. A quantum mechanical system or particle that is bound, confined spacially can only take on certain discrete values of energy as opposed to classical particles which 2. 4).

Heating by low-energy cosmic rays

The first mechanism proposed for heating the ISM was heating by low energy cosmic rays. For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on Cosmic rays transfer energy to gas (through both ionization and excitation) and to free electrons through Coulomb interactions. Low energy cosmic rays (a few MeV) are more important because they are far more numerous than high-energy cosmic rays. Cosmic rays are an efficient heating source able to penetrate in the depths of molecular clouds.

Photoelectric heating in grains

The ultraviolet radiation emitted by hot stars can remove electrons from dust grains. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The photon hits the dust grain and some of its energy is used in overcoming the potential energy barrier (due to the possible positive charge of the grain) to remove the electron from the grain. The remainder of the photon's energy heats the grain and gives the ejected electron kinetic energy. The kinetic energy of an object is the extra Energy which it possesses due to its motion Since the size distribution of dust grains is:

where r is the size of the dust particle, the grain area distribution is:

This indicates that the smallest dust grains dominate this method of heating.

Photoionization

When an electron is freed from an atom (typically from absorption of a UV photon) it carries kinetic energy away of the order: E_photon − E_ionization. This heating mechanism dominates in HII regions, but is negligible in the diffuse ISM due to the relative lack of neutral carbon atoms.

X-ray heating

X-rays remove electrons from atoms and ions, and those photoelectrons can provoke secondary ionizations. As the intensity is often low, this heating is only efficient in warm, less dense atomic medium (as the column density is small). For example in molecular clouds only hard x-rays can penetrate and x-ray heating can be ignored. This is assuming the region is not near an x-ray source such as a supernova remnant. A supernova remnant ( SNR) is the structure resulting from the gigantic explosion of a Star in a Supernova.

Chemical heating

Molecular hydrogen (H₂) can be formed on the surface of dust grains when 2 H atoms (which can travel over the grain) meet. This process yields 4. 48 eV of energy distributed over the rotational and vibrational modes, kinetic energy of the H₂ molecule, as well as heating the dust grain. This kinetic energy, as well as the energy transferred from de-excitation of the hydrogen molecule through collisions heats the gas.

Grain-gas heating

Collisions at high densities between gas atoms and molecules with dust grains can transfer thermal energy. This is not important in HII regions because UV radiation is more important. It is also not important in diffuse ionized medium due to the low density. In the neutral diffuse medium grains are always colder, but do not effectively cool the gas due to the low densities.

Grain heating by thermal exchange is very important in supernova remnant where densities and temperatures are very high.

Gas heating via grain-gas collisions is dominant deep in giant molecular clouds (especially at high densities). Far infrared radiation penetrates deeply due to the low optical depth. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Dust grains are heated via this radiation and can transfer thermal energy during collisions with the gas. A measure of efficiency in the heating is given by the accommodation coefficient:

where T is the gas temperature, T_d the dust temperature, and T₂ the post-collision temperature of the gas atom/molecule. This coefficient was measure by Burke & Hollenbach (1983) as α = 0. 35.

Other heating mechanisms

A variety of macroscopic heating mechanisms are present including:

• Gravitational collapse of a cloud
• Supernova explosions
• Stellar winds
• Expansion of H II regions
• Magnetohydrodynamic waves created by supernova remnants

Cooling of the interstellar medium

Fine structure cooling

This process is dominant in most regions of the ISM, except regions of hot gas and regions deep in molecular clouds. Gravitational collapse in Astronomy is the inward fall of a massive body under the influence of the force of Gravity. A supernova (plural supernovae or supernovas) is a stellar Explosion. A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a Star. An H II region (also known as Emission nebula) is a cloud of glowing Gas and plasma, sometimes several hundred Light-years across Magnetohydrodynamics (MHD ( magnetofluiddynamics or hydromagnetics) is the Academic discipline which studies the dynamics of electrically This occurs most efficiently with abundant atoms having fine structure levels close to the fundamental level such as: CII and OI in the neutral medium and OII, OIII, NII, NIII, NeII and NeIII in HII regions. Collisions will excite these atoms to upper levels, which will eventually de-excite through photon emission, which will carry the energy out of the region.

Cooling by permitted lines

At higher temperature more levels than fine structure levels can be populated via collisions. For example collisional excitation of the n=2 level of hydrogen will release a Lyα photon upon de-excitation. In molecular clouds excitation of rotational lines of CO is important.

References

• Bacon, Francis (1626), Sylva 
• Beals, C. Francis Bacon 1st Viscount St Alban KC QC (22 January 1561 – 9 April 1626 was an English Philosopher, Statesman, and author S. (1936), “On the interpretation of interstellar lines”, Monthly Notices of the Royal Astronomical Society 96: 661, <http://adsabs.harvard.edu/abs/1936MNRAS..96..661B> 
• Birkeland, Kristian (1913), “Polar Magnetic Phenomena and Terrella Experiments”, The Norwegian Aurora Polaris Expedition, 1902-03. Kristian Olaf Birkeland ( December 13, 1867 - June 15, 1917) was born in Christiania ( Oslo today and wrote his first , New York: Christiania (Oslo), H. Aschelhoug & Co. , pp. 720 
• Boyle, Robert (1674), Excell. Robert Boyle was a Natural philosopher, chemist physicist inventor and early Gentleman scientist, noted for his work in Physics and Chemistry Theol. ii. iv. : 178 
• Burke, J. R. & Hollenbach, D. J. (1983), “The gas-grain interaction in the interstellar medium - Thermal accommodation and trapping”, Astrophysical Journal 265: 223, <http://adsabs.harvard.edu/abs/1983ApJ...265..223B> 
• Dyson, J. (1997), Physics of the Interstellar Medium, London: Taylor & Francis 
• Field, G. B. ; Goldsmith, D. W. & Habing, H. J. (1969), “Cosmic-Ray Heating of the Interstellar Gas”, Astrophysical Journal 155: L149, <http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1969ApJ...155L.149F> 
• Ferriere, K. (2001), “The Interstellar Environment of our Galaxy”, Reviews of Modern Physics 73 (4): 1031-1066, DOI 10. 1103/RevModPhys. 73. 1031  (astro-ph preprint)
• Haffner, L. M. ; Reynolds, R. J. ; Tufte, S. L. & Madsen (2003), “The Wisconsin Hα Mapper Northern Sky Survey”, Astrophysical Journal Supplement 145: 405, DOI 10. 1086/378850 . The Wisconsin Hα Mapper is funded by the National Science Foundation. The National Science Foundation (NSF is a United States Government agency that supports fundamental Research and Education in all the non-medical
• Heger, Mary Lea (1919), “Stationary Sodium Lines in Spectroscopic Binaries”, Publications of the Astronomical Society of the Pacific 31 (184): 304, <http://adsabs.harvard.edu/abs/1919PASP...31..304H> 
• Lequeux J. The Interstellar Medium. Springer 2005.
• McKee, C. F. & Ostriker, J. P. (1977), “A theory of the interstellar medium - Three components regulated by supernova explosions in an inhomogeneous substrate”, Astrophysical Journal 218: 148, <http://adsabs.harvard.edu/abs/1977ApJ...218..148M> 
• Patterson, R. Christopher Fulton McKee (born 1942 is an Astrophysicist. McKee obtained a Ph Jeremiah (Jerry Paul Ostriker (born 1937) is a distinguished Astrophysicist at Princeton University. H. (1862), Ess. Hist. & Art 10 
• Pickering, W. H. (1912), “The Motion of the Solar System relatively to the Interstellar Absorbing Medium”, Monthly Notices of the Royal Astronomical Society 72: 740, <http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1912MNRAS..72..740P> 
• Spitzer, L. (1978), Physical Processes in the Interstellar Medium, Wiley, ISBN 0471293350 
• Stone, E. William Henry Pickering ( February 15, 1858 &ndash January 17, 1938) was an American Astronomer, brother of Edward Lyman Strong Spitzer Jr ( June 26, 1914 &ndash March 31, 1997) was an American theoretical physicist. C. ; Cummings, A. C. ; McDonald, F. B. ; Heikkila, B. C. ; Lal, N. & Webber, W. R. (2005), “Voyager 1 Explores the Termination Shock Region and the Heliosheath Beyond”, Science 309: 2017, DOI 10. 1126/science. 1117684 
• Thorndike, S. L. (1930), “Interstellar Matter”, Publications of the Astronomical Society of the Pacific 42 (246): 99, <http://articles.adsabs.harvard.edu//full/seri/PASP./0042//0000099.000.html> 

See also

• Cosmic dust
• Diffuse interstellar band
• Interstellar masers
• Interstellar reddening
• Heliosphere
• List of molecules in interstellar space
• Outer Solar System
• Outer space
• Solar system
• Stellar system
• Timeline of knowledge about the interstellar and intergalactic medium
• Intergalactic space
• Interplanetary space

External links

• Freeview Video 'Chemistry of Interstellar Space' William Klemperer, Havard University. A Royal Institution Discourse by the Vega Science Trust.