(via A dying star weaves a spiral in the night | Bad Astronomy | Discover Magazine)
Ooh, wow! This is a shot of R Sculptoris in (sub)millimeter, longer than far infrared and heading into radio waves from ALMA, the Atacama Large Millimeter/submillimeter Array. (As the name might imply, it, like a few other ‘scopes - VLT, VISTA, etc. - is up in the Atacama Desert in Chile.)
In any case, you’ve probably seen this picture of LL Peg, or, at least, I recall blogging it, a dying star so faint that the shell of gas is being lit by other stars in the neighborhood:
That’s from Hubble. You’ll note the spiral structure, but it lacks the shell you can see in the ALMA shot of R Sculptoris.
So what happened?
Both stars are part of binary systems, meaning there’s a decent amount of motion of the star itself around the center of mass.
All stars, when they are dying like this, have a series of thermal pulses that occur as the fusion reactions inside the star go wonky. Specifically, when the helium begins to fuse in a thin shell around the core, it is highly sensitive to temperature, and a slight increase can create runaway fusion, resulting in a sudden ejection of the outer layers of the star. In the case of LL Peg, this didn’t happen very quickly, so the whole thermal pulse and subsequent ejecta were all affected by its binary companion, creating a continuous spiral. (If everything is coming straight off the surface, but the surface is rotating, you get a “garden sprinkler” effect. It looks spiral, even if the actual motion of any one particle is a straight line.)
R Sculptoris, on the other hand, had a sudden, sharp thermal pulse at the beginning (creating a shell, much as non-binary stars do) that expanded so rapidly, its motion dwarfed that induced by the companion star.
Later ejecta from R Sculptoris are slower, so they’re being affected by the orbital dynamics of the binary pair.
There’s a great animation from ESO on this, using the ALMA data.
Just to blow your mind a little more, the amount of energy that one thermal pulse poured into the outer layers of R Sculptoris to move that much material that quickly…is equivalent to the amount of energy our entire Sun emits.