Forming the first planetary systems: debris around Galactic thick disc stars

TL;DR

This study used infrared observations to search for debris disks around old thick disc stars, finding none, which suggests such systems are rare, but some may host giant planets similar to the Solar System.

Contribution

First observational search for debris disks around thick disc stars, providing insights into early planetary system formation in the Galaxy.

Findings

No debris detected around 22 thick disc stars.

Some stars host giant planets despite lack of debris.

Debris disks are rare in this ancient stellar population.

Abstract

The thick disc contains stars formed within the first Gyr of Galactic history, and little is known about their planetary systems. The Spitzer MIPS instrument was used to search 11 of the closest of these old low-metal stars for circumstellar debris, as a signpost that bodies at least as large as planetesimals were formed. A total of 22 thick disc stars has now been observed, after including archival data, but dust is not found in any of the systems. The data rule out a high incidence of debris among star systems from early in the Galaxy's formation. However, some stars of this very old population do host giant planets, at possibly more than the general incidence among low-metal Sun-like stars. As the Solar System contains gas giants but little cometary dust, the thick disc could host analogue systems that formed many Gyr before the Sun.