AB Aurigae

Lore & Background

AB Aurigae was identified as a variable star by Mary Doris Applegate Beach in 1921, after she examined 150 photographic plates taken between 1914 and 1921. The star belongs to the young Taurus-Auriga association within the Taurus Molecular Cloud. It may have recently encountered a dense cloudlet, which disrupted its debris disk and produced an additional reflection nebula.

The star's radio emission suggests the presence of a thermal jet originating from the star. Its protoplanetary disk, imaged by ALMA in 2017, has a radius of about 120 astronomical units and contains a distinct gap. Inside this gap, gaseous spiral arms were detected in CO, best explained by an unseen planet with a semimajor axis of about 60–80 au. An additional planet with a semimajor axis of 30 au and a large pitch angle could explain the emptiness of the inner dusty disk.

In April 2022, a planet-like clump was observed at a projected separation of 93 AU from the star. This clump may be either an accretion disk around a newly formed planet or an unstable disk region transforming into a planet. Evidence for unstable disk regions transforming into companions was reported in a Nature paper published in September 2024, possibly supporting the formation of AB Aurigae b, which was independently detected in July 2022.

Reader's Guide

AB Aurigae is significant as a young stellar object that provides a direct laboratory for studying planet formation. Its protoplanetary disk, imaged with ALMA, reveals spiral arms and a gap that strongly suggest the presence of at least one massive substellar companion. The detection of a planet-like clump in 2022 and subsequent evidence for disk instability transforming into companions (reported in 2024) make this system a key case for understanding how planets form via gravitational instability. The star's membership in the Taurus-Auriga association places it within a well-studied star-forming region, and its variable nature, discovered by Mary Doris Applegate Beach, adds historical context to its study. The system's thermal jet and disrupted debris disk further enrich its role as a benchmark for pre-main-sequence evolution and disk dynamics.

Did You Know?

• AB Aurigae was discovered to be a variable star by Mary Doris Applegate Beach in 1921.
• The star hosts a protoplanetary disk with a radius of about 120 astronomical units.
• The star is part of the young Taurus-Auriga association in the Taurus Molecular Cloud.