is the gas and dust from earlier stars which have exploded. The explosions are largely responsible for the creation of the chemical elements and for the spread of this matter, in the form of clouds, out of which new stars are formed.
he gas and dust between the stars that fills the plane of the galaxy. For centuries, scientists believed that the space between the stars was empty. It wasn't until the eighteenth century, when William Herschel observed nebulous patches of sky through his telescope, that serious consideration was given to the notion that interstellar space was something to study. It was only in the last century that observations of interstellar material suggested that it is not uniformly distributed through space, but rather has its own unique structure.
interstellar clouds of gas and dust. More than sixty molecular species have been discovered in the interstellar medium including carbon monoxide, alcohol and formaldehyde. Most of the matter of the interstellar medium is hydrogen with some dust grains composed mainly of ice particles (carbon and silicates).
ISM; The gas and dust particles that exists between the stars everywhere in a galaxy. In most places it is extremely tenuous; the average density of atoms is only about 1 per cubic cm. The elemental composition of the gas is roughly 75% H and 25% He (this came out of the Big Bang), plus small amounts of O, C, N, and heavier atoms (all of which have been manufactured in stars). Astronomers like to refer to elements heavier than He as 'metals'.
(ISM): The term astronomers to describe all gas and dust in the plane of the galaxy that exists "between the stars." The ISM can be ionized if it is diffuse and near a radiation source (such as a star), but the denser more isolated regions of the ISM typically consist entirely of molecules both in the gas phase and frozen onto dust grains.
The interstellar medium is the dust and gas (mostly hydrogen) that are between stars in a galaxy. The interstellar medium is no very dense at all; at its densest, it is emptier than the best vacuum we can produce on Earth.
The interstellar medium (or ISM) is the name astronomers give to the gas and dust that pervade interstellar space. While the ISM refers to the matter 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.