Astrophysics (Index)About

interstellar medium

(ISM, interstellar matter)
(matter within a galaxy between star systems)

The interstellar medium (ISM) is matter such as gas and dust between stars. (Matter between entire galaxies is called the intergalactic medium.) Depending upon circumstance, the gas may be ionized, neutral, or molecular. Number density varies from as little as 1 per 10,000 cm3 to 1,000,000 per cm3 (compared to about 2.5×1019 per cm3 for dry air at sea level). The ISM's existence was first deduced through observed absorption lines (interstellar absorption lines), especially as noticed as common to stars close together within the celestial sphere, thus showing the effects of passing through material in front of them.

There is a nesting of types of ISM:

The hot ionized medium (HIM) often results from supernovae, and is referred to as coronal gas because its temperature (and perhaps other characteristics) are comparable to the gas of the Sun's corona.

The term cloud is used for regions with particular characteristics, such as a higher density, which may be termed an interstellar cloud, gas cloud, dust cloud, dense cloud, etc.

A diffuse interstellar band (DIB) is an absorption spectral band affecting observations of stars and other objects. Such bands are attributed to polycyclic aromatic hydrocarbons in the ISM.

Further reading:

Referenced by pages:
Balmer jump (BJ)
bipolar outflow
bow shock
methylidyne (CH)
infrared cirrus
cold gas
cosmic dust
dark matter halo
dense core mass function (DCMF)
diffuse interstellar bands (DIBs)
dispersion measure (DM)
diffractive interstellar scintillation (DISS)
extragalactic background light (EBL)
energetic neutral atom (ENA)
extreme ultraviolet (EUV)
star formation feedback
fast radio burst (FRB)
galactic disk
galactic electron density
gamma rays (GR)
glycine (Gly)
hydrogen cyanide (HCN)
helium 1083 nm line
Herbig-Haro object (HH)
HII region (HII)
HI region (HI)
HI supershell
homologous collapse
hydrogen (H)
ionization correction factor (ICF)
intergalactic medium (IGM)
Interstellar Medium Absorption Profile Spectrograph (IMAPS)
interstellar astrophysics
interstellar holography
ionizing radiation
interplanetary medium (IPM)
lithium (Li)
Local Bubble
magnesium (Mg)
magnetic field
mass density
magnesium lines (Mg lines)
magnetohydrodynamics (MHD)
natural astronomical telescopes
plasma astrophysics
plasma frequency
pulsar (PSR)
pulsar wind nebula (PWN)
radio supernova (RSN)
refractive interstellar scintillation (RISS)
RT instability
Sloan Digital Sky Survey (SDSS)
shock wave
submillimeter galaxy (SMG)
supernova remnant (SNR)
solar wind
stellar wind