Dear PF Forum, I've read the current Featured Thread in November 12nd, Lost in the Milky Way scenario. It's a good thread. But I want know what pulsar is. https://en.wikipedia.org/wiki/Pulsar A. Does pulsar(s) have unique frequency? Given the number of pulsar in our galaxy and the vast range of pulsar frequency, so it's unlikely that there are two pulsars that have a similar frequency in our galaxy. B. The implication of question A is Does pulsar(s) frequency remain stable for at least million of years? C. Is there a formula to create pulsar frequency? I mean: For a star say 1 solar mass that have the ratio of hydrogen/helium and perhaps carbon combinations the star will behave the same as our sun. And given some times the star will explode as our sun. Or there is a limit for neutron star mass, if I'm not mistaken it's between 1.5 solar mass to 3 solar mass. So what about pulsar frequency, is that really random generated? D. In Voyager plate, there is a picture about pulsar, I just realized that now. Because the only thing that I can recall from that plate that I first read it when I was in junior high is the naked man/woman picture. Can't remember the 3rd rock from the star, the pulsar and the 2 hydrogen circles. The scientists that designed it (Sagan? Drake?) carved some pulsars with their frequency. (as they say, because I don't even know what is it all about if I found that plaque in my backyard). So what I want to know is: Supposed an alien civilization encounter that plate, how will they know the frequency of the pulsars given just the length radius of the picture. (If they somehow can decipher that it's about pulsars) Thank you very much.