{"response":"{\"What is gravitational Doppler shift?

Gravitational Doppler shift is when sound or light changes pitch because of gravity, just like when a siren on a fire truck sounds higher as it zooms toward you and lower as it zooms away.

Imagine you're playing with your friend who has a toy siren. When they run toward you, the sound changes, it gets higher. When they run away, it gets lower. That’s the Doppler effect.

Now imagine that same siren is on a spaceship far away in space. If the spaceship zooms toward Earth, the sound (or light) from the siren changes too, just like before. But here's the twist: gravity can also change how the sound or light reaches us, like when it’s coming from something really heavy, such as a black hole.

If your friend is standing on a very high hill and plays their siren, you might hear it differently than if they were right next to you. The same thing happens with stars or planets, gravity can stretch or squish the sound (or light) that reaches us, changing how it sounds or looks.

It's like listening to your friend’s toy siren through a thick blanket, it changes the way the sound comes through!