The origin of rotation profiles in star-forming clouds

Abstract

Angular momentum distribution and its redistribution are of crucial importance in the formation and evolution of circumstellar disks. Many molecular line observations toward young stellar objects indicate that radial distributions of the specific angular momentum j have a characteristic profile. In the inner region, typically R < ∼ 100 AU, the specific angular momenta distribute like j ∝ r 1/2 , indicating existence of rotationally supported disk. In outer regions, R > ∼ 5000 AU, j increases as the radius increases and the slope is steeper than unity, which is supposed to reflect the original angular momentum distributions in the maternal molecular clouds. In the intermediate region, 100 AU < ∼ R < ∼ 5000AU, j-distribution appears almost flat. While this is often interpreted as a consequence of conservation of the specific angular momentum, the interpretation actually is insufficient and requires a stronger condition that the initial distribution of j must be spatially uniform. However, this requirement seems to be unrealistic and inconsistent with observations. In this work, we propose a simple alternative explanation; the apparently flat j profile is produced by strong elongation due to the large velocity gradient in the accreting flow no matter what the initial j distribution is. To show this we provide a simple analytic model for gravitational collapse of molecular clouds. We also propose a method to estimate ages of protostars using solely the observed rotation profile. We demonstrate its validity in comparison with hydrodynamic simulations, and apply the model to young stellar objects such as L1527 IRS, TMC-1A and B335.

Thermal desorption of formamide and methylamine from graphite and amorphous water ice surfaces

“…Therefore, in the context of prestellar cores, a very high binding energy also prevents any return in the gas phase. The second efficient mechanism for populating the gas phase is the chemical desorption (or reactive desorption) (Takahashi & Williams 2000;Garrod et al 2007;Dulieu et al 2013). Here, the energy released during the formation of the molecule itself is the promoter of the desorption.…”

The diverse lives of massive protoplanets in self-gravitating discs

“…Recent ALMA observations of the disc of the young star HL Tau (ALMA Partnership et al 2015) have revealed the presence of multiple gaps at mm wavelengths. These gaps may be carved either by planets (Dipierro et al 2015) or be due to other processes (Takahashi & Inutsuka 2014;Gonzalez et al 2015;Takahashi et al 2016b). HL Tau is an extremely young object (Greaves et al 2008) that shows signs of outflows in the form of jets and infall from its parent cloud.…”

Gravitational lensing of a star by a rotating black hole

“…Time dependences for the observed star position on the celestial sphere, radiation flux from the star, frequency of detected radiation, major and minor semiaxes of the lensed star image have been calculated and plotted. The detailed observation of such lensing requires a space interferometer such as the Russian Millimetron project.It is expected that the Event Horizon Telescope [1-8] will measure in the next three years the shape of shadow [9-17] of the supermassive black SgrA* hole at the center of the Galaxy, illuminated by either a hot background gas and stars [18][19][20][21][22] or an accretion disk [23][24][25][26][27][28][29]. A black hole at the center of giant elliptic galaxy M87 is another promising candidate for measuring the shape of black hole shadow.…”

“…It is expected that the Event Horizon Telescope [1-8] will measure in the next three years the shape of shadow [9-17] of the supermassive black SgrA* hole at the center of the Galaxy, illuminated by either a hot background gas and stars [18][19][20][21][22] or an accretion disk [23][24][25][26][27][28][29]. A black hole at the center of giant elliptic galaxy M87 is another promising candidate for measuring the shape of black hole shadow.…”