Nebula
An interstellar cloud of dust, hydrogen, helium, and ionized gases in space, serving as a site for star formation.
Governing formula
M_Jeans = (5 k_B T / (G μ m_H))^(3/2) (3 / (4 π ρ))^(1/2)
SI unit
Light-Years (Diameter)
In depth
Classified into emission nebulae (glowing ionized gas), reflection nebulae (scattering starlight), dark nebulae (dense light-blocking dust), planetary nebulae (ejected white dwarf envelopes), and supernova remnants.
Examples in the real world
The Orion Nebula (M42) acting as an active stellar nursery forming new young stars.