Rotating neutron star (6)
I believe the answer is:
pulsar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">rotating neutron star</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for pulsar that I've seen before include "Rapidly rotating star, emitting electromagnetic waves very quickly" , "Rapidly fluctuating star" , "Radio-emitting star" , "Star producing radio waves" , "A source of space of radio signals" .)