Bipolar outflow
A bipolar outflow comprises two continuous flows of gas from the poles of a star. Bipolar outflows may be associated with
Protostars
In the case of a young star, the bipolar outflow is driven by a dense, collimated jet.[1] These
Occurrence
Typically, molecular bow shocks are observed in
Bipolar outflows are usually observed in emission from warm carbon monoxide molecules with millimeter-wave telescopes like the James Clerk Maxwell Telescope, though other trace molecules can be used. Bipolar outflows are often found in dense, dark clouds. They tend to be associated with the very youngest stars (ages less than 10,000 years) and are closely related to the molecular bow shocks. Indeed, the bow shocks are thought to sweep up or "entrain" dense gas from the surrounding cloud to form the bipolar outflow.[2]
Jets from more evolved young stars -
The presence of a bipolar outflow shows that the central star is still accumulating material from the surrounding cloud via an accretion disk. The outflow relieves the build-up of angular momentum as material spirals down onto the central star through the accretion disk. The magnetised material in these protoplanetary jets is rotating and comes from a wide area in the protostellar disk.[1]
Bipolar outflows are also ejected from evolved stars, such as
In both cases, bipolar outflows consist largely of molecular gas. They can travel at tens or possibly even hundreds of kilometers per second, and in the case of young stars extend over a parsec in length.
Galactic outflow
Massive galactic molecular outflows may have the physical conditions such as high gas densities to form stars. This star-formation mode could contribute to the morphological evolution of galaxies.[7]
See also
- Accretion disc
- Astrophysical jet
- Bipolar nebula
- Herbig–Haro object
- Planetary nebula
References
- ^ Reipurth B., Bally J. (2001), "Herbig–Haro flows: probes of early stellar evolution", Annual Review of Astronomy and Astrophysics, vol. 39, p. 403-455
- ^ Davis C. J., Eisloeffel J. (1995), "Near-infrared imaging in H2 of molecular (CO) outflows from young stars", Astronomy and Astrophysics, vol. 300, p. 851-869.
- ^ Kwok S. (2000), The origin and evolution of Planetary Nebulae, Cambridge Astrophysics Series, Cambridge University Press.
- ^ Chen Z., Frank A., Blackman E. G., Nordhaus J. and Carroll-Nellenback J., (2017), "Mass Transfer and Disc Formation in AGB Binary systems", Monthly Notices of the Royal Astronomical Society, https://doi.org/10.1093/mnras/stx680