Accretion flow in a contracting magnetized isothermal cloud was studied using magnetohydrodynamical simulations and a nested grid technique. First, the interstellar magnetized cloud experiences a ``runaway collapse'' phase, in which the central density increases drastically within a finite time scale. Finally, it enters an accretion phase, in which inflowing matter accretes onto a central high-density disk or a new-born star. We found that the accretion rate reaches (4--40)times c_s(3/G) , where c_s and G represent the isothermal sound speed and the gravitational constant, respectively. This is much larger than the standard accretion rate of 0.975c_s(3/G) for a hydrostatic isothermal spherical cloud (Shu 1977, AAA 19.065.044). Due to the effect of an extra infall velocity achieved in the runaway phase ( ~ 2c_s), the accretion rate is boosted. This rate declines with time in contrast to Shu's solution, but keeps >~ 2.5c_s(3/G) . The observed gas infall rate around proto-stars such as L1551 IRS 5 and HL Tau is also discussed.
Publications of the Astronomical Society of Japan
- Pub Date:
- October 1996
- INTERSTELLAR: CLOUDS;
- INTERSTELLAR: MEDIUM;
- STARS: FORMATION;
- 10 pages, latex using PASJ style file (available from http://www.tenmon.or.jp/pasj/index-e.html), postscripted text and figures are available from http://quasar.ed.niigata-u.ac.jp/docs/Papers/mag3ps.tgz