University of Auckland scientist helps uncover exceedingly rare pair of stars

Of the billions of stars in our galaxy, two have been identified as vanishingly rare by University of Auckland astrophysicist Professor Jan Eldridge. Photo / TIO/NOIRLab/NSF/AURA/P. Marenfeld

Among hundreds of billions of stars in our galaxy, two have been identified as vanishingly rare by University of Auckland astrophysicist Professor Jan Eldridge and her international collaborators.

Located in a constellation near Sirius, the brightest star in the night sky, the pair may be one of only about 10 such pairs in the galaxy, according to Eldridge.

As a world expert on the evolution of binary stars, pairs of stars which orbit each other, Eldridge’s computer modelling helped establish the stars’ story.

The research has been published in leading journal Nature and is attracting attention around the world, including this article published by CNN.

Many people know of supernovae, massive stars exploding with colossal force as they run out of nuclear fuel in their cores. The cores collapse and the explosions create neutron stars.

University of Auckland astrophysicist Professor Jan Eldridge. Photo / Supplied

What Eldridge and colleagues have found is something much rarer, a scenario where the supernova was a fizzer, like a damp firecracker… a wimpy supernova. With a regular supernova, the force of the explosion gives the neutron star a big kick, so it flies off at hundreds of kilometres per second and develops an elliptical orbit.

But that didn’t happen in this case. The gravitational pull of the neighbouring star stole most of the mass of the exploding star, leading to a weaker explosion, called an “ultra-stripped supernova”. So there was no big kick, and consequently no elliptical orbit.

“What really sets this system apart is the circular orbit, much like the Earth going around the Sun,” says Eldridge. “This star system has evolved in a very rare and strange way.”

The two stars will eventually create a kilonova, as the pair collide and explode, releasing gold and other elements.

Making computer models of how stars are born, live and die, what you could call a “synthetic universe”, Eldridge’s research helps to establish the meaning of astronomers’ observations.

“Stars make the elements needed for life, so understanding stars is to understand where we come from,” she says.

The research was carried out with colleagues including at Embry-Riddle Aeronautical University in the US. The binary system’s name is CPD-29 2176 and it’s in the constellation Puppis.