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.
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.