If we see a nebula by looking through a powerful telescope, how can we tell whether we are looking at the remnant of a supernova or at a planetary nebula? Thanks
A Supernova Remnant contains a Black Hole or a Neutron Star while a Planetary Nebula contains a White Dwarf.
Also, Supernovae Remnants are likely to have great velocities, so Doppler is another plausible choice. - Not through telescope though.