how do astronauts communicate with each other in space even though there is no medium for the sound to travel? even if they use walkie-talkies still they cant send voice messages as they will not be heard normally. they themselves cannot hear what they have to say.so how is that possible?

Dear Student, 

The astronauts have a special astronaut suit to wear while they are out in space. This suit has a special radio transmitter which converts the sound signals into radio signals and vice versa. Thus in vacuum, the sound is transmitted and received in form of radio waves. 

Hope it helps!
Regards