Astronomy and Astrophysics – Astronomy
Scientific paper
May 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...19513506v&link_type=abstract
American Astronomical Society, 195th AAS Meeting, #135.06; Bulletin of the American Astronomical Society, Vol. 32, p.883
Astronomy and Astrophysics
Astronomy
Scientific paper
The hypothesis of triggered, or assisted, star formation suggests that star formation may in some cases be initiated by outside factors, such as interstellar shock waves. The proposal augments the standard theory of star formation, which assumes stars to form in quiescent conditions without external interference. The scenario is also relevant in the context of the solar system: the best explanation for the presence of short-lived radioactivities in the early solar system is that the nuclides were produced in a nearby stellar nucleosynthesis site and transported to the molecular cloud core from which the solar system formed by a shock wave, which also triggered the collapse of the core. The viability of the triggered star formation scenario is investigated through numerical simulations studying the processes involved in the impact of a shock wave on a molecular cloud core. The calculations suggest that molecular cloud cores can be triggered into collapse by shock waves traveling at 10-45 km s-1. Higher-velocity shocks tear the cloud apart, while lower-velocity shocks do not compress the core sufficiently to initiate collapse. Radioactivities carried by the shock wave can be injected into the collapsing system through Rayleigh-Taylor instabilities developing at the surface of the core. Injection begins shortly after the central density of the core has started to grow due to the shock wave transmitted from the compressed outer regions of the core and proceeds steadily for 400,000 yr. The injection efficiency is 10-20%, and the fraction of injected material is typically 0.7% of the total mass contained in the central parts of the collapsing core. The timescale of triggered collapse is 100,000 yr, sufficiently short for the radioactivities to have survived in the measured amounts. This work was supported by NASA Origins of Solar Systems Program grant NAG5-4306.
Boss Alan P.
Vanhala Harri A. T.
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