Did our Solar System form in a bubble?

A study from the University of Chicago suggests a new scenario for the birth of our Solar System.

An illustration showing how bubbles around a massive star evolve over millions of years (moving clockwise from top left).
Credit: V. Dwarkadas & D. Rosenberg


Our Solar System may have formed in a large bubble around a giant, long-dead star, according to a study.

The new theory could explain an oddity in the proportion of two isotopes present in the early Solar System.

The prevailing theory suggests our Solar System formed billions of years ago near a supernova, which are exploded stars.

But this new study theorises that the story of our Solar System begins with a Wolf-Rayet star. These stars are more than 40 - 50 times the size of our Sun and burn incredibly hot.

As they do so, they release elements into the space via stellar winds. These stellar winds hit the material surrounding the star, forming a bubble-like structure with a dense shell.

As dust and gas becomes trapped inside this shell, it coalesces and condenses to form stars. It is thought that 1 to 16 per cent of Sun-like stars form this way.


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This new theory could help solve a mystery regarding two isotopes present in the early Solar System.

Meteorites from that period reveal there was an abundance of aluminium-26 at that time, while other studies have revealed there was not as much iron-60. These proportions do not match the porportions in the rest of the Galaxy at that time.

This is problematic for the supernova theory of how our Solar System formed, because supernovae produce both isotopes.

Wolf-Rayets however, release lots of aluminium-26, but no iron-60.


A simulation showing how stellar winds carry mass from a giant star over the course of millions of years, forming bubbles around it.
Simulation by V. Dwarkadas/D. Rosenberg, via GIPHY



“The idea is that aluminum-26 flung from the Wolf-Rayet star is carried outwards on grains of dust formed around the star," says coauthor of the study Vikram Dwarkadas, a research associate professor in astronomy and astrophysics at the University of Chicago.

“These grains have enough momentum to punch through one side of the shell, where they are mostly destroyed, trapping the aluminum inside the shell.”

If our Solar System did form around a Wolf-Rayet star, the star would have died long ago, perhaps exploding as a supernova or collapsing into a black hole.

If it collapsed into a black hole, it would have produced little iron-60.

If it exploded, the iron-60 created in the supernova may not have penetrated the bubble walls, or may have been distributed unequally.


Carousel image: the Carina Nebula, surrounding a Wolf Rayet star.
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