What is the thick black wire behind stock radio in Chevy cobalt?

[W3$]

Does anyone know what it is? It's a thick black wire thats behind the stock radio and it actually runs in the radio. It's not just plugged into it. Plz help?
And to install an aftermarket head unit I would have to cut this wire from the stock head unit?

 

[darrell c]

That is the antenna wire for the radio stations

 

[Josh W]

antenna wire

 

[inktownlegend]

antenna wire, you just pull it out