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known distance (125 pc), and temperature (16 K), Barnard 68 has a physical radius of 12,500 AU, a mass of 2.1 solar masses, and a
 

Summary: known distance (125 pc), and temperature (16 K), Barnard 68 has a
physical radius of 12,500 AU, a mass of 2.1 solar masses, and a
pressure at its boundary of P 2:5 3 102 12
Pa. This surface pres-
sure is an order of magnitude higher than that of the general
interstellar medium22
but it is in rough agreement with the pressure
inferred for the Loop I superbubble from X-ray observations with
the ROSAT satellite13
. The close correspondence of the observed
extinction pro®le with that predicted for a Bonnor±Ebert sphere
strongly suggests that Barnard 68 is indeed an isothermal, pressure-
con®ned and self-gravitating cloud. It is also likely to be in a state
near hydrostatic equilibrium with thermal pressure primarily
supporting the cloud against gravitational contraction.
For Barnard 68, ymax is very near and slightly in excess of the
critical radial parameter and the cloud may be only marginally
stable and on the verge of collapse. However, in the likely case that
the cloud contains a static magnetic ®eld23±25
, the additional internal

  

Source: Adams, Philip W. - Department of Physics and Astronomy, Louisiana State University

 

Collections: Materials Science