Bok globule

Star formation
Object classes
Interstellar medium Molecular cloud Bok globule Dark nebula Young stellar object Protostar T Tauri star Herbig Ae/Be star Herbig–Haro object
Theoretical concepts
Initial mass function Jeans instability Kelvin–Helmholtz mechanism Nebular hypothesis Planetary migration
Star portal
v t e

An image of Thackeray's Globules, a set of Bok globules in the H II region IC 2944, taken with the WFPC2 instrument on the Hubble Space Telescope

Bok globules are dark clouds of dense cosmic dust and gas in which star formation sometimes takes place. Bok globules are found within H II regions, and typically have a mass of about 2^[1] to 50 solar masses contained within a region about a light year or so across (about 4.5 × 10⁴⁷ m³, see Orders of magnitude (volume)).^[2] They contain molecular hydrogen (H₂), carbon oxides and helium, and around 1% (by mass) of silicate dust. Bok globules most commonly result in the formation of double or multiple star systems.^[3]

Bok globules were first observed by astronomer Bart Bok in the 1940s. In a paper published in 1947, Bok and E.F. Reilly hypothesized that these clouds were 'similar to insect's cocoons' that were undergoing gravitational collapse to form new stars from which stars and star clusters were born.^[4] This hypothesis was difficult to verify due to the observational difficulties of establishing what was happening inside a dense dark cloud that obscured all visible light emitted from within it. An analysis of near infrared observations published in 1990 confirmed that stars were being born inside Bok globules.^[5] Further observations have revealed that some Bok globules contain embedded warm sources,^[2] some contain Herbig-Haro objects,^[6] and some show outflows of molecular gas.^[7] Millimeter-wave emission line studies have also provided evidence for the infall of material onto an accreting protostar.^[8]

Bok globules are still a subject of intense research. Known to be some of the coldest objects in the natural universe, their structure and density remains somewhat a mystery. Methods applied so far have relied on column density derived from near infrared extinction and even star counting in a bid to probe these objects further.

Bok globules that are blasted by nearby stars exhibit fragmentation of materials to produce a tail. These types are called "cometary globules" (CG).^[9]

See also

• Molecular cloud
• IC 2944

References

External links

Wikimedia Commons has media related to Bok Globule.

• A Star in the Making

v t e Star Evolution Formation Pre-main-sequence star Main sequence Horizontal branch Asymptotic giant branch Dredge-up Instability strip Red clump PG1159 star Mira variable Planetary nebula Protoplanetary nebula Luminous red nova Luminous blue variable Wolf–Rayet star Supernova impostor Supernova Hypernova Hertzsprung–Russell diagram Color–color diagram Protostars Molecular cloud H II region Bok globule Young stellar object Herbig–Haro object Hayashi track Hayashi limit Henyey track Orion T Tauri FU Orionis Herbig Ae/Be Luminosity class Subdwarf Dwarf Blue Red White Black Brown Subgiant Giant Blue Red Bright giant Supergiant Blue Red Yellow Hypergiant Yellow Blue straggler Spectral classification O B A F G K M Be OB Subdwarf B Late-type Peculiar Am Ap/Bp Oscillating Barium Carbon CH Extreme helium Lambda Boötis Lead Mercury-manganese S Shell Technetium Remnants White dwarf Black dwarf Helium planet Neutron star Pulsar Magnetar Stellar black hole Compact star Quark Exotic Stellar core: EF Eridani B Theoretical stars Dark-matter star Frozen star Quasi-star Thorne–Żytkow object Iron star Nucleosynthesis Alpha process Triple-alpha process Proton–proton chain Helium flash CNO cycle Lithium burning Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova Remnants Structure Core Convection zone Microturbulence Oscillations Radiation zone Atmosphere Photosphere Starspot Chromosphere Corona Stellar wind Bubble Asteroseismology Eddington luminosity Kelvin–Helmholtz mechanism Properties Designation Dynamics Effective temperature Kinematics Magnetic field Magnitude Absolute Mass Metallicity Rotation UBV color Variability Star systems Binary Contact Common envelope Multiple Accretion disc Planetary system Earth's Solar System Earth-centric observation of Pole star Circumpolar star Magnitude Apparent Extinction Photographic Color Radial velocity Proper motion Parallax Photometric-standard star Lists Star names Arabic Chinese Most massive Least massive Largest Brightest Historical Most luminous Nearest Nearest bright Stars with exoplanets Brown dwarfs Collapsars Planetary nebulae Novae Notable supernovae Supernova remnants Supernova candidates Timeline of stellar astronomy Related articles Substellar object Brown dwarf Sub-brown dwarf Planet Star cluster Association Open cluster Globular cluster Super star cluster Galactic year Galaxy Supercluster Helioseismology Guest star Constellation Asterism Gravity Intergalactic star Infrared dark cloud Star portal