Massive, erratic, binary Luminous Blue Variable star Eta Carina, with its Homunculus shell, comes to mind.Stephen Clark wrote:This image from NASA’s Chandra X-ray Observatory shows spiral galaxy NGC 7331,
center, in a three-color X-ray image. Red, green and blue colors are used for low,
medium and high-energy X-rays, respectively. An unusual supernova called
SN 2014C has been spotted in this galaxy, indicated by the box.
Credit: NASA/CXC/CIERA/R.Margutti et al
The supernova SN 2014C dramatically changed in appearance over the course of a year, apparently because it had thrown off a lot of material late in its life. ...
Astronomers classify exploding stars based on whether or not hydrogen is present in the event. While stars begin their lives with hydrogen fusing into helium, large stars nearing a supernova death have run out of hydrogen as fuel. Supernovae in which very little hydrogen is present are called “Type I.” Those that do have an abundance of hydrogen, which are rarer, are called “Type II.”
But SN 2014C, discovered in 2014 in a spiral galaxy about 36 million to 46 million light-years away, is different. By looking at it in optical wavelengths with various ground-based telescopes, astronomers concluded that SN 2014C had transformed itself from a Type I to a Type II supernova after its core collapsed(...) Initial observations did not detect hydrogen, but, after about a year, it was clear that shock waves propagating from the explosion were hitting a shell of hydrogen-dominated material outside the star. ...
To create this shell, SN 2014C did something truly mysterious: it threw off a lot of material — mostly hydrogen, but also heavier elements — decades to centuries before exploding. In fact, the star ejected the equivalent of the mass of the Sun. Normally, stars do not throw off material so late in their life. ...
Why would the star throw off so much hydrogen before exploding? One theory is that there is something missing in our understanding of the
nuclear reactions that occur in the cores of massive, supernova-prone stars.
Another possibility is that the star did not die alone — a companion star in
a binary system may have influenced the life and unusual death of the
progenitor of SN 2014C. This second theory fits with the observation that
about seven out of 10 massive stars have companions. ...