Study of polluted white dwarfs reveals stars and planets ‘grow’ together

(ORDO NEWS) — A team of astronomers have discovered that planet formation in our young solar system began much earlier than scientists thought, with the building blocks of the planets growing at the same time as the parent star.

A study of some of the oldest stars in the universe suggests that the building blocks of planets like Jupiter and Saturn begin to form as a young star grows.

Planets were thought to form only after a star reaches its final size, but new results published in the journal Nature Astronomy suggest that stars and planets “grow” together.

The study, led by the University of Cambridge, is changing understanding of how planetary systems formed.

“We have a pretty good idea of ​​how planets form, but one unresolved question we have is when do they form.

Does planetary formation start early, when the parent star is still growing, or does it happen millions of years later? said Dr. Amy Bonsor, author of the study.

To try to answer this question, Bonsor and her colleagues studied the atmospheres of white dwarfs ancient, faint remnants of stars like our Sun.

Usually the interiors of planets are out of reach of telescopes. But “polluted” white dwarfs contain such heavy elements as magnesium, iron and calcium.

These elements must have originated from small bodies, such as asteroids, that were left behind after the formation of planets and then crashed into white dwarfs and burned up in their atmospheres.

With spectroscopic observations of polluted white dwarfs, scientists can probe the interiors of these torn apart asteroids.

Planet formation is thought to begin in a protoplanetary disk made up mostly of hydrogen, helium, and tiny particles of ice and dust orbiting a young star.

According to the current leading theory about how planets form, dust particles stick to each other, eventually forming ever larger solids.

Some of them will continue to grow into planets, and some will remain as asteroids like those that crashed into white dwarfs in the current study.

The researchers analyzed spectroscopic observations of the atmospheres of 200 polluted white dwarfs from nearby galaxies.

According to the analysis, the mixture of elements observed in the atmospheres of these dwarfs can only be explained if many of the original asteroids once melted, causing heavy iron to sink into the core while lighter elements floated to the surface.

“The reason for the melting can only be very short-lived radioactive elements that exist in the very early stages of the development of the planetary system, but decay in just a million years,” Bonsor said.

“In other words, if these asteroids were melted down by something that only existed for a very short time at the dawn of the planetary system, then the process of planet formation should start very quickly.”

The study suggests that the picture of early formation is likely correct, meaning that Jupiter and Saturn have had enough time to grow to their current sizes.

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