  We present combined Submillimeter-Array (SMA) + single-dish images of the
(sub)millimeter dust continuum emission toward two prestellar cores SM1 and
B2-N5 in the nearest star cluster forming region, $\rho$ Ophiuchus. Our
combined images indicate that SM1 and B2-N5 consist of three and four
condensations, respectively, with masses of $10^{-2}-10^{-1}M_\odot$ and sizes
of a few hundred AU. The individual condensations have mean densities of
$10^8-10^9$ cm$^{-3}$ and the masses are comparable to or larger than the
critical Bonner-Ebert mass, indicating that the self-gravity plays an important
role in the dynamical evolution of the condensations. The coalescence timescale
of these condensations is estimated to be about $10^4$ yr, which is comparable
to the local gravitational collapse timescale, suggesting that merging of the
condensations, instead of accretion, plays an essential role in the star
formation process. These results challenge the standard theory of star
formation, where a single, rather featureless prestellar core collapses to form
at most a couple of condensations, each of which potentially evolves into a
protostar that is surrounded by a rotating disk where planets are created.
