A champagne flow is an astrophysical event whereby an

HII region An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds ...

inside a molecular cloud expands outward until it reaches the interstellar medium. At that point, the ionized

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

bursts outward like an uncorked champagne bottle. This event is also sometimes called a Blister. An HII region is created by ionization from a recently formed star (usually an O-star) inside a molecular cloud. The champagne model is perhaps one of the first numerical calculations of the propagation of ionisation fronts and of the expansion of

s that did not assume a constant density medium around the massive exciting

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

. The model assumes that

star formation Star formation is the process by which dense regions within molecular clouds in The "medium" is present further soon.-->interstellar space

takes place in a dense cloud, surrounded and in pressure equilibrium with a low density inter-cloud gas. The ample supply of

UV photon Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

s generated by the star rapidly establishes an HII region and the expansion of this, sooner or later allows also for the ionisation of the inter cloud gas. Ionisation disrupts then the former pressure balance between the cloud and the inter-cloud gas as under the stellar radiation field all photo-ionised gas acquires a temperature of the order of 10000 K. In this way, the ionised cloud material acquires an excess pressure, a pressure larger than the ionised low density inter cloud gas and this provoques the supersonic expansion of the ionised cloud matter into the surrounding gas (the champagne flow). The streaming of matter out of the cloud allows for the ionisation of a larger portion of the original cloud sustaining in this way the pressure imbalance which eventually leads to the complete disruption of the parent cloud. The terms champagne model and champagne flow were coined by

Mexican Mexican may refer to: Mexico and its culture *Being related to, from, or connected to the country of Mexico, in North America ** People *** Mexicans, inhabitants of the country Mexico and their descendants *** Mexica, ancient indigenous people ...

astrophysicist Guillermo Tenorio-Tagle in a paper in 1979 (Astronomy and Astrophysics 1979A&A....71...59T). The model focus on the size, velocity field and the large density variations observed in HII regions. This article was followed by further

hydrodynamical In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and ...

calculations in one and two dimensions, in collaboration with Drs. Peter Bodenheimer, Harold W. Yorke and Piet Bedijn see:1979ApJ...233…85B.1983A&A...127..313Y, 1979A&A....80..110T, 1982ASSL...93….1T, 1984A&A...138..325Y, 1981A&A....98…85B

References

Further reading