Because of the distances involved, a supernova could have occured today, but we wouldn't know about it for thousands or billions of years. As with all things in space, what we observe is what was, not what is.
See related questions for last observed supernova.
It is iron.
No, a supernova is an explosion of a star. What left of a supernova are celestial bodies.
It is yes
No, not a supernova.
supernova
it is a steller explosion
A supernova.
Supernova
SuperNova
Supernova
supernova
supernova