- Our solar system could have formed inside a bubble of a massive star type called Wolf-Rayet star.
- These stars were nearly 50 times bigger than our Sun, and their cores were more than a million years old.
- Like supernova explosion, the life of massive Wolf-Rayet star ended long ago.
Despite numerous astonishing discoveries about the universe in the last couple of decades, scientists are still not sure how our solar system formed. The complete story remains a mystery. However, this time, researchers at the University of Chicago come up with a comprehensive theory, explaining the complete story of solar system.
What we know is solar system formed near a supernova approximately 4.6 billion years ago. But the theory fails to explain the lack of the isotope Iron-60, nor does it address the abundance of the isotope Aluminum-26 in infant solar system.
This research suggests a new scenario that starts with a massive star type named Wolf-Rayet star, which is nearly 50 times bigger than our Sun. Our solar system could have formed inside this massive Wolf-Rayet bubble. The study addresses a nagging cosmic mystery of proportion of these 2 isotopes (Iron-60 and Aluminum-26) in the solar system, as compared to the rest of the galaxy.
A study done in 2015 revealed that there was a lot of Aluminum-26 and less of isotope Iron-60 in the early solar system. This arose a question, why one isotope injected into the solar system while other was not. This is what made scientists to study Wolf-Rayet stars that ejects much amount of Aluminum-26, but no Iron-60.
Simulation of bubbles around giant star evolving over millions of years (clockwise from top left)
The shell of Wolf-Rayet bubble is a perfect place to form stars, because gas and dust get trapped inside where they could condense into stars. According to the researchers, between 1 and 16 percent of all stars (similar to Sun) could be formed in such stellar nurseries.
What researchers have suggested is the aluminum isotope flung from the Wolf-Rayet star is carried outwards on dust grains formed in the neighborhood of the star. Such grains have higher momentum – high enough to pass through one side of the shell, while most of them destroying themselves and trapping aluminum inside the shell.
In wind-driven bubbles, proceeding outwards in radius, one can identify five distinct regions –
- A freely expanding wind
- A shocked wind region
- A photoionized region
- A thin dense shell
- The external medium
A wind termination shock can separate the freely expanding wind from the shocked wind. The external boundary is a radiative shock that compresses the swept-up material to generate a thin and dense shell, enclosed between radiative shock and contact discontinuity on the inside.
Simulations showing how stellar winds carry mass from a massive star over millions of years, creating bubbles around it.
The cores of Wolf-Rayet stars were around 100,000 to greater than a million years old. Both theoretical and observational considerations suggest a high probability of triggered star formation at the boundaries of wind-blown bubbles, where suitable conditions are predicated and observed.
Like supernova explosion, the life of massive Wolf-Rayet star ended long ago. Moreover, supernova explosion would produce Iron-60 but it would not be capable enough to penetrate the bubble walls, or was distributed unequally.
When it comes to what humans know about space history, nothing is really for certain, but it is certainly a fascinating theory that deserves further analysis.