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. 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. Even though the interstellar gas is very dilute, the amount of matter adds up over the vast distances between the stars. The cold clouds of neutral or molecular hydrogen are the birthplace of new stars if they become gravitationally unstable and collapse.