Astronomers Spot Second-Generation Planet-Forming Disks around Ancient Binary Stars

by johnsmith

Astronomers have assembled a catalog of all known Galactic binaries featuring massive disks of gas and dust that are similar to the protoplanetary disks that are known to surround young stars.

An artist’s impression of a transition disk around an evolved binary star. Image credit: N. Stecki.

An artist’s impression of a transition disk around an evolved binary star. Image credit: N. Stecki.

“Planets such as Earth, and all other planets in our Solar System, were formed not long after the Sun,” said Dr. Jacques Kluska from the KU Leuven Institute of Astronomy and colleagues.

“Our Sun started to burn 4.6 billion years ago, and in the next million years, the matter around it clumped into protoplanets.”

“The birth of the planets in that protoplanetary disk, a gigantic pancake made of dust and gas, so to speak, with the Sun in the middle, explains why they all orbit in the same plane. But such disks of dust and gas needn’t necessarily only surround newborn stars.”

“They can also develop independently from star formation, for example around binary stars of which one is dying (binary stars are two stars that orbit each other, also called a binary system),” they added.

“When the end approaches for a medium-sized star (like the Sun), it catapults the outer part of its atmosphere into space, after which it slowly dies out as a so-called white dwarf.”

“However, in the case of binary stars, the gravitational pull of the second star causes the matter ejected by the dying star to form a flat, rotating disk.”

“Moreover, this disk strongly resembles the protoplanetary disks that astronomers observe around young stars elsewhere in the Milky Way.”

“This we already knew. However, what is new is that the discs surrounding so-called evolved binary stars not uncommonly show signs that could point to planet formation.”

In the new research, Dr. Kluska and co-authors indeitified 85 such binary stars with massive disks.

“In 10% of the evolved binary stars with disks we studied, we see a large cavity (a void/opening, ed.) in the disk,” Dr. Kluska said.

“This is an indication that something is floating around there that has collected all matter in the area of the cavity.”

“We also saw that heavy elements such as iron were very scarce on the surface of the dying star,” he added.

“This observation leads one to suspect that dust particles rich in these elements were trapped by a planet.”

“The confirmation or refutation of this extraordinary way of planet formation will be an unprecedented test for the current theories,” said Professor Hans Van Winckel, head of the KU Leuven Institute of Astronomy.

The team’s work was published online in the journal Astronomy & Astrophysics.


J. Kluska et al. 2022. A population of transition disks around evolved stars: Fingerprints of planets. Catalog of disks surrounding Galactic post-AGB binaries. A&A 658, A36; doi: 10.1051/0004-6361/202141690

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