Globulets

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Globulets ( Latin - French globules ) are narrowly defined areas within a star formation area in which substellar objects are formed. They differ from globules in their smaller mass, which is why globulets are the precursor objects for brown dwarfs or unbound exoplanets . Globulets have a temperature of only a few Kelvin above absolute zero in their outer areas , which is why stable dust exists in these small molecular clouds . The globulets can therefore be observed as dark points in front of bright HII areas .

Globulets show no signs of a protostar in the far infrared . Their diameter is less than 10,000  astronomical units , with a typical value of 2,500 AU. The total mass of most globulets is less than 13  Jupiter's masses and is thus in the range between brown dwarfs and planets .

Globulets often lie near a faint filament of the nebula that is in a state of dissolution. They probably arise as a product of the removal of filaments or other structures of the nebula. Globulets show a relative speed of 5 to 10 km / s compared to their HII area. This is probably caused by the rocket effect: the side facing the fog is heated up and evaporated, which accelerates the globulette.

Their shape is often round and, unlike globules, shows no signs of a bright edge, which is caused by photoevaporation of an early star; only a few globulets show the typical teardrop shape of the propolyds . Simulation calculations show a shock triggered by photoevaporation, which can lead to a gravitational collapse. In some of the globulets, an exoplanet or brown dwarf has already formed before the UV radiation of early stars completely dissolves , which survives the photoevaporation and wanders through the Milky Way as an unbound object . These unbound exoplanets have been detected indirectly through gravitational lensing .

literature

  • T. Grenman, GF Gahm: The tiny globulettes in the Carina Nebula . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1404.2255v1 (English).
  • P. Gratier et al .: Dense molecular “globulettes” and the dust arc towards the runaway O star AE Aur (HD 34078) Nebula . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1403.6597v1 (English).
  • GF Gahm et al .: Mass and motion of globulettes in the Rosette Nebula . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1305.2485v2 (English).