Dying stars may also still produce planets, according to research by international scientists led by KU Leuven. Until now it was only known that planets form around young stars. The discovery could potentially lead to a major overhaul of current theories about planet formation.
The earth was formed fairly quickly, less than ten million years after the sun was formed. Other planets in our solar system also formed relatively quickly. So it was assumed that planets form from ‘young’ stars. That also means that planets are usually not much older than the stars they orbit.
It now appears that dying stars can also give rise to planets. To do this, the researchers looked at so-called evolved binary stars in our Milky Way. Evolved binary stars are two stars that revolve around a common center of gravity. One of the two stars is a star that is at the end of its life. When a single star dies, it catapults the outermost part of its atmosphere into space and then slowly dies out. In binary stars, however, the gravity of the living star forces the ejected matter from the dying star into a flat rotating disk around the two. Those disks are also very similar to those that astronomers observe around young stars elsewhere in the Milky Way.
The researchers also found signs of planet formation in those flat disks of the binary stars. The scientists examined 85 such binary star pairs and found a large ‘cavity’ at 10 percent, meaning a large opening can be seen in the flat disk. “That indicates that something is floating around there that has gathered all the matter at the height of the cavity,” explains astronomer Jacques Kluska (KU Leuven). “Looks like that’s the work of a planet.”
The researchers also saw that certain elements, such as iron, were only present to a limited extent. “That suggests that matter particles rich in these elements were scavenged by a planet.”
Adjusting current theories
The discovery is unexpected, says Kluska. “We did an inventory of evolved binary stars in our Milky Way. Being able to formulate this hypothesis is extraordinary. It would mean that current theories about planet formation would have to be adjusted.”
The astronomers want to verify their hypothesis themselves. To do this, they will study the ten binary star pairs whose disc of matter shows a large cavity, with the large telescopes of the European Southern Observatory in Chile.
The study is published in the scientific journal Astronomy & Astrophysics.
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