Bubbles Forming Around 40-solar-mass Star
Graphic taken from a simulation which shows how bubbles form over the course of 4.7 million years around a Wolf-Rayet star. V. Dwarkadas/D. Rosenberg

The question of how exactly our solar system formed has long puzzled scientists, despite the significant advances that have been made in the field of astronomy over the past few decades.

But in a new study, published in the Astrophysical Journal, researchers from the University of Chicago have outlined a new theory that sheds light on the issue.

They suggest that our solar system formed billions of years ago in a vast "bubble" of gas and dust around a giant, long-dead star, contradicting the commonly held view which suggests a nearby supernova was responsible for its creation.

The dead star in question is what scientists call a Wolf-Rayet star. These are more than 40 to 50 times the size of our own Sun and burn hotter than any other stars, producing vast quantities of material – much of which is blown off the surface by intense stellar winds.

This process eventually creates a huge 'bubble' of gas and dust with a dense 'shell' around the star.

"The shell of such a bubble is a good place to produce stars," because dust and gas become trapped inside eventually condensing into stars, said Nicolas Dauphas, co-author of the study.

In fact, between 1% and 16% of all sun-like stars form in stellar nurseries such as these, according to the researchers.

The new explanation diverges from the supernova hypothesis in order to make sense of the mystery surrounding two compounds – aluminium-26 and iron-60 – which occur in strange proportions in the early solar system.

Scientists know that our solar system had a lot more aluminium-26 and much less iron-60 when compared to the rest of the galaxy, which is puzzling because supernovae produce both of these materials.

"It begs the question of why one was injected into the solar system and the other was not," said Vikram Dwarkadas, another co-author of the study.

The team looked to Wolf-Rayet stars for an explanation because they produce lots of aluminium-26, but no iron-60.

"The idea is that aluminium-26 flung from the Wolf-Rayet star is carried outwards on grains of dust formed around the star," Dwarkadas said. "These grains have enough momentum to punch through one side of the shell, where they are mostly destroyed – trapping the aluminium inside the shell. Eventually, part of the shell collapses inward due to gravity, forming our solar system."

The researchers suggest that the Wolf-Rayet star which may have given birth to our solar system, and consequently all life on Earth, most likely exploded in a supernova or collapsed into a black hole long ago.

If it became a black hole, little iron-60 would have been produced, but if it created a supernova, it is possible that any iron-60 produced would not have penetrated the walls of the bubble – accounting for the low levels of the compound in the early solar system.