At the most basic level, we struggle with questions like “how do stars and planets form?” and “how do stars change the composition of the universe over time?”
For the longest time (by which I mean since we really started trying to model what’s going on) we thought stars had to be well on their way to being fully formed – a million years old or so – before the disks around them began to form planets. In broad brushstrokes, our story said that a collapsing cloud of gas and possibly dust would fragment into cocoons or proplyds in which a star would form.
Over time, the core of this knot of material would become dense enough and hot enough that nuclear reactions would begin, and that protostar would light up and begin interacting with the infalling material around it. Some of the material around the newly forming star would eventually collapse into planets, and a solar system would be born. The exact details of this story have been unclear, and it seems that each new theory has been undone by the next new observation.
Well, today’s newly published observations show that even this level of broad understanding was totally wrong.
New images from the Atacama Large Millimeter/submillimeter Array (ALMA) show evidence of a dust ring with gaps circling IRS 63, a protostar less than 500,000 years old. This co-existence of a forming planetary disk and a forming star seems to indicate that stars and planets form side by side and are roughly the same age.
This work is published in the latest issue of Nature and is led by Dominique Segura-Cox, who writes: We used to think that stars entered adulthood first and then were the mothers of planets that came later. But now we see that protostars and planets grow and evolve together from early times, like siblings.
Co-author Ian Stephens goes on to say: These rings and gaps suggest that we are seeing the earliest evidence of planet formation and that planets certainly start to form within the first half million years, and probably within the first 150,000 years. Planets, especially planets like Jupiter, started their own formation at one of the earliest stages of the star formation process.
Over time, it is my hope that observers using ALMA and other high-resolution systems that work in the infrared and radio will be able to observe systems spanning the entire planet formation process. Then eventually we can put together essentially a film of star and planet evolution that may catch each stage through a different star system but that allows us to see the entirety of the process, the same way that walking the halls of a hospital will allow you to see human growth from birth to death in the myriad faces on the different floors.
“Four Annular Structures in a Protostellar Disk Less Than 500,000 Years Old,” D. M. Segura-Cox et al., 2020 Oct. 7, Nature