"A Star That Would Not Die" - https://spaceref.com/science-and-exploration/a-star-that-wou...

Interesting

If you want to go down the rabbit hole watch this video from suspicious0bservers.org.

Start at 7:24 to skip the intro.

https://www.youtube.com/watch?v=B_zfMyzXqfI

Binary stars are so common, it surprises me to find so few phenomena that involve companions. It was gratifying to see suggested a neutron star diving through a diffuse neighbor.

There are of course type Iä supernovas. ("Fhtagn!")

This is definitely an interesting object, but based on the recent literature[0] it seems most astronomers attribute the odd signatures to interactions with its circumstellar material. The Wikipedia article focuses a bit too much on the initial Nature paper authored by Arcavi et al...

[0] https://ui.adsabs.harvard.edu/search/fq=%7B!type%3Daqp%20v%3...

The article says this is a Type II-P supernova; the wikipedia link says that's a core-collapse supernova, and results in a neutron star. It says the collapse of the core occurs in seconds. I suppose the production of heavy elements and radiation must continue for days or weeks.

If a big star's core collapses to a neutron star in seconds, and the outer parts of the star get blown away due to reaching escape velocity, how does this thing keep blazing for four years? Is it really not a core-collapse supernova?

The most likely hypothesis seems to be that there is a lot of interstellar material around the star, such that the ejecta is colliding with that and keeping it hot to keep glowing. It was a core-collapse supernova initially; the energy released from that is being absorbed and more slowly re-emitted by the thick surrounding material. (Thick in astronomical terms is still something like a microgram of hydrogen per cubic meter.)

Yeah, that's roughly what I figured (IANAA). But it still seems hard to explain six flashes bright enough to appear like a supernova. I'd expect the flash of any kind of supernova to be brighter than the flash of a shockwave hitting a shell of gas. But I know nothing.

And anyway, for the shockwave from a supernova explosion to hit the shell of expanding gas from a previous explosion, that still seems to imply two supernova explosions from the same star. The only way I know that can happen is in a binary system.

Perhaps it’s a hybrid? Original core collapse, then accretion of in falling material after the shock from the last explosion dissipates, causing spontaneous fusion/degeneracy again and re-explosion?

There’s a hypothesis it’s actually three stars in close proximity, which we see as a single star from our point of view. The hypothesis goes on to state this tri-star system undergoes Chaotic Eras, followed by Stable Eras. During the Chaotic Eras, the three stars come extreme close proximity, wrecking havoc on potential planets and moons in the system. Some scientists are trying to predict when they might next observe this false Supernova illusion, given the last time it occurred and these stars’ distance from Earth. Unfortunately, no closed form solution to this three body problem exists.