星前核心中的星下质量凝聚
Substellar-Mass Condensations in Prestellar Cores
摘要：
我们提出了组合的亚毫米阵列（SMA）+单碟图像的（亚）毫米尘埃连续排放向两个星前核心SM 1和B2-N5在最近的星团形成区，$ρ$蛇夫座。我们的综合图像表明，SM 1和B2-N5分别由三个和四个凝聚体组成，质量为$10^{-2}-10^{-1}M_\odot$，大小为几百AU。单个凝聚体的平均密度为$10^8-10^9$ cm $^{-3}$，质量接近或大于临界Bonner-Ebert质量，表明自引力在凝聚体的动力学演化中起着重要作用.这些凝聚的合并时间尺度估计约为$10^4$年，这是可比的本地引力坍缩的时间尺度，这表明合并的凝聚，而不是吸积，在恒星形成过程中起着至关重要的作用。这些结果挑战了恒星形成的标准理论，即一个单一的，而不是无特征的星前核心坍缩形成最多几个凝聚体，每个凝聚体都可能演变成一个原恒星，被一个旋转的圆盘包围，行星在那里产生。
英文摘要：
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, $ρ$ 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.
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