A protostar is a very young star that is still gathering mass from its parent molecular cloud. It is the earliest phase in the process of stellar evolution. For a low-mass star, it lasts about 500,000 years. The phase begins when a molecular cloud fragment first collapses under the force of self-gravity and an opaque, pressure-supported core forms inside the collapsing fragment. It ends when the infalling gas is depleted, leaving a pre-main-sequence star, which contracts to later become a main-sequence star at the onset of hydrogen fusion producing helium.
Infant star CARMA-7 and its jets are located approximately 1400 light-years from Earth within the Serpens South star cluster.
Illustration of the dynamics of a proplyd
HBC 1 is a young pre-main-sequence star.
Protostar outburst - HOPS 383 (2015).
A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, H2), and the formation of H II regions. This is in contrast to other areas of the interstellar medium that contain predominantly ionized gas.
Astronomer Henk van de Hulst first theorized hydrogen could be traceable in interstellar space using radio signals.
Plaque commemorating the discovery of 21-cm radiation from the Milky Way
Left to right: Jan Oort, Hendrik C. van de Hulst, Pieter Oosterhoff. Jan Oort had a pivotal role in the research that lead to the discovery of molecular clouds.
Penzias and Wilson with the Holmdel horn antenna used to detect microwave emissions from the Big Bang