Carbon object to Unix timestamp based on timezone

I have a datetime string of format 'Y-m-d H:i:s', and datetime value as '2018-01-30 07:11:21'.

$carbon_obj = Carbon::createFromFormat('Y-m-d H:i:s' , '2018-01-30 07:11:21','America/Chicago');

How do it get the Unix timestamp from this carbon object?

via Chebli Mohamed