Accreting Protoplanets in the LkCa 15 Transition Disk

TL;DR

This study presents direct evidence of accreting protoplanets within the transition disk LkCa 15, using adaptive optics to detect Hα emission indicative of active accretion onto a young planet.

Contribution

First direct detection of accretion signatures onto a protoplanet within a transition disk, confirming the presence of actively forming planets in such environments.

Findings

Detected multiple companions on Keplerian orbits.

Observed Hα emission indicating active accretion.

Provided evidence for hot gas (~10,000 K) accreting onto a protoplanet.

Abstract

Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1900 exoplanets have now been discovered and confirmed, none are still in the process of formation. Transition discs, protoplanetary disks with inner clearings best explained by the influence of accreting planets, are natural laboratories for the study of planet formation. Some transition discs show evidence for the presence of young planets in the form of disc asymmetries or infrared sources detected within their clearings, as in the case of LkCa 15. Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful. Here we report adaptive optics observations of LkCa 15 that probe within the disc clearing. With accurate source positions over multiple epochs spanning 2009 - 2015, we infer the presence of multiple companions on Keplerian orbits. We directly detect H{\alpha} emission from the innermost companion, LkCa 15 b, evincing hot (~10,000 K) gas falling deep into the potential well of an accreting protoplanet.