This happens because galaxies are spatially extended objects composed of billions of stars, and are vulnerable to tidal forces. What you get looks like an eliptical galaxy. We are not presently being good galactic citizens because we are not transmitting anything for anyone else to hear. We are, however, listening carefully to see if anyone else out there is trying to talk to us. For instance, visible light is out because the stars would interfere.
Human activity produces more radio waves than the sun.
A good project might be to propose a sensible way to send a signal to an extraterrestrial civilization, and determine how far away it could be detected. It is thought that they started out as a much larger spherical cloud of hydrogen gas, with no stars. Somehow, by gravitational collapse, this cloud of gas must have collapsed into something like a disk, and then made stars. In addition to the stars in the galactic disk, there are many more stars which are found bundled into compact clusters about 20 light years in radius, containing about 1 million stars each, known as globular clusters. These clusters are loosely associated with the galaxy, most being located quite far from the main disk.