There are times when the press releases we receive miss the true wildness of what our universe is throwing at astronomers to try and figure out.

During recent observations of the system HD 74438, astronomers realized they weren’t looking at one star or even two stars, but they were looking at four stars — four fairly young, not very massive stars that are twinned together in an evolving dance. Still located in the open cluster in which they formed, these stars currently aren’t all that different from our Sun. Two of them are a bit bigger and shine a bit hotter. And two are a bit smaller and cooler. Looked at today, this is just a neat system that has two tight binary systems that are orbiting one another.

What is just a neat system today, however, may one day become a system that experiences all the wildest forms of stellar evolution as it potentially works its way toward an eventual explosion.

Multi-star systems like this are constantly changing. The complex gravitational tugs pull the stars into stretched-out orbits and can even drive them into collision courses over time. Mass will get pulled to and fro, and the four normal stars we see today will lose mass, pass mass, and maybe even combine masses.

In a new paper in the journal Nature, researchers led by Thibault Merle use computer models to work through all the different possibilities. It isn’t possible to say exactly what will happen; there is no single solution for how these kinds of stars will orbit in the long term, and when you start factoring in the changing sizes of their lives, and things like mass loss, there are a lot of possibilities. 

With computers, it is possible to see what is most likely. In about half the models, the stars remain four separate stars, but in the other half of the models, they get close enough that two or three of the stars will spiral together, heat one another up, and become surrounded by a shared stellar atmosphere.

This is a far, far future possibility – it’s stuff that will occur when some to all of the stars are compact white dwarfs – and this kind of merger will essentially take multiple elder stars and give them new life as a single younger star.

And in those situations where the system ends up with one white dwarf orbiting around that new, combined mass, star – in that one possible kind of future, which can be reached in more than one way – the last white dwarf can do as white dwarfs sometimes do and gravitationally steal material from that one companion star that used to be three stars. And if it steals enough mass and hits a critical mass, it will explode as a type 1a supernova.

I feel pretty comfortable saying this research team found perhaps the most convoluted way to produce a supernova.

To summarize: researchers found four stars orbiting together, and if they evolve just right, three of those stars will die, merge together and be reborn, and then feed their atmosphere to a fourth star, and that mass will make that fourth star explode.

Go science? One of the most amazing things about our universe is that we actually have the capacity to understand it.

More Information

University of Canterbury press release

“A spectroscopic quadruple as a possible progenitor of sub-Chandrasekhar type Ia supernovae,” Thibault Merle et al., 2022 May 12, Nature Astronomy