Formation Of Exoplanet AB Aurigae b Detected in H-alpha Light

Small rocky planets like Earth, which can harbor life, and giant gas planets like Jupiter are born around stars like the Sun. Their birthplace is a thin, disk-shaped structure of gas and dust known as a protoplanetary disk.

Protoplanetary disks are observed not only around Sun-like stars but also around more massive or lighter young stars. Since the 2010s, their detailed structures have been revealed by 8-meter class telescopes such as the Subaru Telescope (in visible and infrared light) and the ALMA Observatory (in radio wavelengths).

Although many planets have been inferred indirectly from fine structures in these disks—such as gaps or spiral arms—directly capturing newly formed planets (protoplanets) within the disks has so far been achieved only in a few cases, including PDS 70 b and c and AB Aurigae b (AB Aur b).

This is thought to be because most protoplanets are embedded within the disk, and become more visible only when they carve gaps in the disk or are observed from directly above. Protoplanets are also considered to be actively gathering material from the surrounding disk as they grow.

However, detailed spectroscopic observations of this mass accretion from an embedded disk have, until now, been limited to the PDS 70 system. In the present study, an international team of researchers led by the Astrobiology Center (Japan) and the University of Texas at San Antonio (USA) succeeded in detecting hydrogen emission lines from AB Aur b using the multi-object spectrograph MUSE mounted on the VLT.

These emission lines are interpreted as evidence of mass accretion from the circumplanetary disk onto the protoplanet.

VLT/MUSE Detection of the AB Aurigae b Protoplanet with Hα Spectroscopy, The Astrophysical Journal Letters (open access)

Astrobiology, Exoplanet,