beecee Posted November 21, 2018 Posted November 21, 2018 https://phys.org/news/2018-11-reveals-universe-secret-ingredients-life.html Study reveals one of universe's secret ingredients for life: November 21, 2018 by Will Wright, Australian National University: A new study led by ANU has investigated the nature of a cosmic phenomenon that slows down star formation, which helps to ensure the universe is a place where life can emerge. Lead researcher Dr. Roland Crocker from the ANU Research School of Astronomy and Astrophysics said the research team studied a particular way stars provide a counter-pressure to gravity that slows down the star-formation process. "If star formation happened rapidly, all stars would be bound together in massive clusters, where the intense radiation and supernova explosions would likely sterilise all the planetary systems, preventing the emergence of life," he said. "The conditions in these massive star clusters would possibly even prevent planets from forming in the first place." Read more at: https://phys.org/news/2018-11-reveals-universe-secret-ingredients-life.html#jCp the paper: https://academic.oup.com/mnras/article-abstract/481/4/4895/5113483?redirectedFrom=fulltext Radiation pressure limits on the star formation efficiency and surface density of compact stellar systems: Abstract The large columns of dusty gas enshrouding and fuelling star formation in young, massive stellar clusters may render such systems optically thick to radiation well into the infrared. This raises the prospect that both ‘direct’ radiation pressure produced by absorption of photons leaving stellar surfaces and ‘indirect’ radiation pressure from photons absorbed and then re-emitted by dust grains may be important sources of feedback in such systems. Here, we evaluate this possibility by deriving the conditions under which a spheroidal, self-gravitating, mixed gas-star cloud can avoid catastrophic disruption by the combined effects of direct and indirect radiation pressure. We show that radiation pressure sets a maximum star cluster formation efficiency of εmax ∼ 0.9 at a (very large) gas surface density of ∼105M⊙∼105M⊙ pc−2(Z⊙/Z)≃20(Z⊙/Z)≃20 g cm−2(Z⊙/Z)(Z⊙/Z), but that gas clouds above this limit undergo significant radiation-driven expansion during star formation, leading to a maximum stellar surface density very near this value for all star clusters. Data on the central surface mass density of compact stellar systems, while sparse and partly confused by dynamical effects, are broadly consistent with the existence of a metallicity-dependent upper limit comparable to this value. Our results imply that this limit may preclude the formation of the progenitors of intermediate-mass black holes for systems with Z≳0.2Z⊙Z≳0.2Z⊙.
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