The ionization of the neutral gas in an interstellar molecular cloud plays a key role in the cloud's evolution, helping to regulate the heating and cooling processes, the chemistry and molecule formation, and coupling the gas to magnetic fields.
Ultraluminous infrared galaxies (ULIRGs), powered by starburst activity and often with supermassive black holes accreting material at their nuclei, contain large reservoirs of molecular gas. This is to be expected: Molecular gas is the raw material for new stars and moreover the presence of the infrared luminous warm dust implies an abundance of molecular gas.
The binary star system Her X-1 consists of a 1.5 solar-mass neutron star – the super-dense, collapsed remnant of a massive star – in orbit around the 2.2 solar-mass star, HZ Herculis.
