Astronomers Found Spirals Inside a Dust Gap of a Young Star Forming Disk

15 May, 2017

Scientific Paper

Planets form within disks composed of dust grains and gas. Planets can gather dust grains from their orbits, resulting in dust gaps or cavities, and can also cause spiral waves within the parental disks based on theoretical predictions. To understand where and when planets can form at early stages, ALMA’s capability of seeing disk material with high resolution can depict smoking-gun evidence of infant planets hidden in disks.

Both dust gaps and spirals have been seen separately in a handful of disks. The new ALMA images of AB Aurigae clearly depict gas spirals inside a wide dust gap. These first reported gas spirals within a dust gap might indicate that there are at least 2 planets within this system. One planet at a distance of 80 astronomical units (au; the distance between the Sun and Earth) from the star is required to create the sharp dust ring. An additional planet at 30 au or closer from the star is required to produce such spirals.

These gas spirals further provide an additional dimension to our understanding of planet- disk interaction. Spirals previously seen in the near infrared image appear at the inner edge of the newly detected gas spirals. This can happen when the gas spirals are puffed up and thus scatter more stellar light at locations closer to the star. The kinematics of gas within the spirals mostly follows the disk rotation. It is only at the putative planet location at 30 au from the star that gas has higher velocities, suggesting streaming motions near the planet.

ALMA image of the dust ring (red) and gaseous spirals (blue) of the circumstellar disk AB Aurigae reveal gaseous spiral arms inside a wide dust gap, providing a hint of planet formation. Credit: ALMA (ESO/NAOJ/NRAO)/Tang et al. | Download image

Additional information

This research is presented in a paper titled “Planet Formation in AB Aurigae: Imaging of the Inner Gaseous Spirals Observed inside the Dust Cavity” by Y.-W. Tang et al., published in the Astrophysical Journal

