It's a safe bet that this superova was artificially caused.
More like the writers didn't know jack shit about it.

And where did he even want to deploy it? At the center of the supernova, or somewhere near Romulus? And what the hell did he even want to do with that black hole? What purpose did that have? Suck back the entire shockwave? Ridiculous. Vacusuck the part of the shockwave that would hit Romulus? How happy would the entire Romulan star system feel if there suddenly was a black hole inside it?Mind you, how could Spock hope to deploy the red matter if he wasn't close to the wave front?