OB stars are hot,

massive star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

s of spectral types O or early-type B that form in loosely organized groups called OB associations. They are short lived, and thus do not move very far from where they formed within their life. During their lifetime, they will emit much

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

radiation. This radiation rapidly

ionize Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

s the surrounding interstellar gas of the

giant molecular cloud A molecular cloud—sometimes called a stellar nursery if star formation is occurring within—is a type of interstellar cloud of which the density and size permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen ...

, forming an H II region or Strömgren sphere. In lists of spectra the "spectrum of OB" refers to "unknown, but belonging to an OB association so thus of early type".

References

* *

External links

* Bouy, Hervé and Alves, João
Cosmography of OB Stars in the Solar Neighborhood
Astronomy & Astrophysics (December 2015). A three-dimensional map of OB star density within 500 pc of the Sun.

— Scientia Astrophysical Organization's star classification page * Philippe Stee's homepage
Hot and Active Stars Research
O-type stars B-type stars {{stellar-astronomy-stub

See also

References

External links