The letter reports VLBI observations of neutral hydrogen absorption in front of quasar 3C 147. The results show a variation in the optical depth of interstellar H I with a scale no larger than 0.16 arcsec. Assuming that a cloud of higher density superposed on a slowly varying background is being observed, a column density of 10 to the 20th power atoms/sq cm is estimated for the H I cloud along with a maximum probable distance of 600 pc, a linear diameter of 70 AU, a density of 100,000 atoms/cu cm, and a mass of 3 ten-millionths of a solar mass. It is noted that this cloud is smaller by several orders of magnitude than any H I cloud previously observed and that its size and density are more similar to those associated with dense molecular clouds.
No takes yet. Share an insight, caveat, or question.
Dieter et al. (1976) studied this question.