ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Detection of Extremely High-density Compact Structure of Prestellar Cores and Multiple Substructures Within

Prestellar cores are self-gravitating dense and cold structures within molecular clouds where future stars born. They expected, at the stage of transitioning to protostellar phase, harbor centrally concentrated (sub)structures that will seed formation a new star or binary/multiple stellar systems. Characterizing this critical evolution is key our understanding formation. In work, we report detection high density on thousand-au scale in sample prestellar cores. Through recent ALMA observations towards Orion cloud, have found five extremely cores, which regions $\sim$ 2000 au size, several $10^7$ $cm^{-3}$ average density. Masses these range 0.30 6.89 M$_\odot$. {\it For first time}, higher resolution (0.8$'' \sim $ 320 au) further reveal one shows clear signatures fragmentation; such individual substructures/fragments sizes 800 -1700 au, masses 0.08 0.84 M$_\odot$, densities $2 - 8\times 10^7$ separations $\sim 1200$ au. The substructures massive enough ($\gtrsim 0.1~M_\odot$) form young objects likely examples earliest embryos can lead widely ($\sim$ 1200 separated multiple