Orbital motion of spiral structures around HD 135344B indicates a hidden protoplanet

Star system: HD 135344 A | Distance from the Sun: 440 light years

The disk surrounding the star HD 135344B shows clear signs of active planet formation, including complex spiral arms and a gap in the surrounding dust. By tracking these features over a ten-year period using various telescopes, researchers have identified a consistent orbital motion that links the spiral structures, a central dust gap, and a mysterious twist in the disk. This evidence suggests that a single, yet-to-be-seen protoplanet is likely responsible for shaping these features.

To analyze the disk, researchers used archival data from multiple observatories to trace the motion of the spiral arms in scattered light. By applying high-fidelity processing techniques to remove image biases, they measured an average orbital speed of 0.81 degrees per year. This measurement confirms that the features are moving in a way consistent with an object orbiting at a distance of approximately 69 astronomical units from the star.

While previous studies claimed to have directly imaged a protoplanet in this system, the new analysis indicates that this signal was likely an artifact of the image processing software rather than a real object. However, the movement of the spiral structures remains a strong indicator of an unseen companion. The study also noted an unexplained trend where the distance of the spiral arms from the central star appears to change depending on the wavelength of light observed.

Key findings
- The orbital motion of the spiral structures is measured at 0.81 degrees per year.
- A previously claimed protoplanet candidate is identified as a processing artifact.
- The observed twist in the disk moves in synchronization with the spiral arms.
- All disk features—spirals, gap, dust, and twist—are likely driven by a single protoplanet.
- Spiral traces show a distance dependence related to the wavelength of observed light.

Scientific study

Multi-epoch scattered-light analysis of HD 135344B: new evidence for a spiral-driving protoplanet (external link)