Astronomy Magazine
Molecular cloud
The cold, dark gas that stars are made out of, and hide inside while forming.
Stars form in clouds of molecular hydrogen and dust at around 10 K, dense enough that gravity can win against pressure once something disturbs them. The dust blocks visible light completely — the dark lanes across the Milky Way are these clouds in silhouette — which is why star formation is studied in infrared and radio, wavelengths that pass through. The Pillars of Creation are a molecular cloud being eroded by the radiation of stars it has already made.
Where it has come up lately
Related terms
Magnetar
A neutron star with a magnetic field a thousand trillion times Earth's.
Supernova (Type Ia and Type II)
Two unrelated ways for a star to explode, useful for two entirely different reasons.
The main sequence
The long, stable middle age a star spends fusing hydrogen in its core.
Hertzsprung–Russell diagram
The single plot that organises everything about stars.
Questions
What is Molecular cloud?
The cold, dark gas that stars are made out of, and hide inside while forming.
Why does it matter?
The dust blocks visible light completely — the dark lanes across the Milky Way are these clouds in silhouette — which is why star formation is studied in infrared and radio, wavelengths that pass through. The Pillars of Creation are a molecular cloud being eroded by the radiation of stars it has already made.