Study Suggests That Dying Stars Can Birth Alien Worlds

Star and planet formation

The processes of formation of stars and their planets are usually closely related. The substance left at the birth of a new star forms a dense disk of gas and dust around it, in which planets appear rather quickly before the disk is cleared and disappears.

For example, the Sun formed 4.6 billion years ago, and a hundred million years later the Earth and other planets already revolved around it.

Just like they form together, they will also die together: when the Sun swells into a red giant and throws off its outer shells, the inner planets will die. More distant ones will persist and remain circling around the dim white dwarf that our star will become.

It would seem that this is an ordinary picture, but the Sun is not an ordinary star. Most stars are part of binary systems and live side by side with at least one neighbor. And if one of them lives longer than the other and turns into a red giant, and then into a white dwarf, then the substance ejected by it can form a new gas and dust disk around the system – and influence the formation of new planets.

Planets can form around dying stars

Jacques Kluska and his colleagues conducted a survey of “secondary” protoplanetary disks in binary systems. In total, they found 85 such objects, and in 10 of them, they found characteristic gaps – lines that draw newborn planets, clearing space along their orbit.

This was also confirmed by the spectra of such stars: judging by them, fewer heavy elements, such as iron, fall on their surface, which means that these substances from the disk partially became part of the newborn planets.

Artist's impression of a binary star system with a disc of dust created by the dying star. Credit: N. Stecki
Artist’s impression of a binary star system with a disc of dust created by the dying star. Credit: N. Stecki

However, such a scenario is far from possible for all stars. A disk can form only under certain conditions and for certain types of stars. To do this, they must exit the asymptotic giant branch, a special late stage of life through which stars with masses from 0.8 to five times the mass of the Sun (including itself) pass.

In addition, the presence of a close partner is required, which could attract the discarded shells. As a rule, this material falls on a neighboring star, but in some cases, it can form a disk. Such a disk cannot exist for a long time and is unlikely to persist for more than a few hundred thousand years. But for the birth of new planets, this is quite enough: our own solar system is well within that time frame.

Scientists suggest that if these planets exist, it would explain certain oddities observed in planetary nebulae, such as the low proportion of refractory elements and minerals in their matter. Of course, astronomers need follow-up observations to confirm their theory.


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Sources:

Fuge, L. (2022, February 1). Dying stars can still give birth to planets. Cosmos Magazine.
Gough, E. (2022, February 4). A second generation of planets can form around a dying star. Universe Today.
Gough, E. (n.d.). Even dying stars could give birth to brand new planets, says study. ScienceAlert.
Kluska, J. (n.d.). A population of transition disks around evolved stars: Fingerprints of planets. Astronomy & Astrophysics.

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