I'm slightly confused as to why and how we record "sounds" from space using radio-waves. Take for example, objects like pulsars on this website: http://www.jb.man.ac.uk/pulsar/Education/Sounds/ So do pulsars really sound like this? Do they actually produce a knocking/ticking sound? Or are these sounds entirely artificial, and just another way of representing the period nature of the "pulses"? Also, can we record "sounds" of objects that emit visible light, instead of radio waves?