How do we figure out the time taken by radio wave to reach earth if we don’t know it’s origin?

Question

I read a news article stating that the scientists detected radio waves that reached earth after 8 billion years.

https://www.moneycontrol.com/science/mysterious-deep-space-radio-signal-reaches-earth-after-8-billion-years-leaving-scientists-puzzled-article-12823408.html/amp

My question is how did we figure out that this wave travelled for 8 billion years ?

In: Physics

Answer 1

We are not sure what process produced it how, but we know the galaxy it’s from. We can measure starlight from that galaxy and determine how much the universe expanded since the light was emitted, which tells us how long the light had to travel. The radio signal has the same speed.