Idler Pulley

On my 1.6 HDI the aux belt has come off, looks like a idler pulley has come off, there is a metal shaft just underneath the power steering pump pulley, looks like the remains of a pulley, but I can't see how the bloody thing comes off, I guess there is a screw or bolt of some sort in the centre, is there some sort of cap on it? and what kind of head does it have?

Thanks in advance.