Somehow I've known about supernovas for many years without realizing that the word and concept "nova" exists as well. It's from the Latin for "new": the appearance of what seems to be a new star, because the star going nova brightened enough to become visible from Earth. (It got picked up from Tycho Brahe describing what we'd now call a supernova, though.)
The mechanism for non-super novas is very interesting: a white dwarf in a binary star system steals hydrogen from the other star, then heats it until it starts to fuse, which blows it all off into space!
I was about to comment that the correct plural form of nova is novae, but it looks like dictionaries say that both novae and novas are correct. The irregular case does seem to predominate according to google ngram viewer.
As far as I know, it’s always valid, and perhaps even preferable, to use the regular -s plural with any Latin loanword, after all they’re English words now even if borrowed from another language. Using the original Latin plural forms in casual contexts feels a bit pretentious, especially when it’s not even the correct form, like "octopi".
It is often the case that as the regular case increases in frequency, it becomes accepted as an alternative. It seems that lexicologists these days are less likely than formerly to insist that the philological roots of a word are the only determinant of correct spelling.
The mechanism for non-super novas is very interesting: a white dwarf in a binary star system steals hydrogen from the other star, then heats it until it starts to fuse, which blows it all off into space!