If you run ps ax without the grep, you'll see the column headers:
PID TT STAT TIME COMMAND ?? is in the TT column -- that's the controlling terminal for the process. The ?? indicates that the process isn't associated with a terminal.
The U in the STAT column indicates that the process is in the uninterruptible sleep state. That explains why you cannot kill it -- is blocked in an uninterruptible sleep in the kernel and cannot be awoken to be terminated. When the process eventually exits the uninterruptible state, it will notice the signal and die.
The numbers in the right are in the COMMAND column -- that's the name of the process. As for what those processes are, I don't know.
