An article published in “The Astrophysical Journal” reports the results of observations of the protoplanetary disk surrounding the very young star TW Hydrae. A team of researchers used observations conducted with the Hubble Space Telescope to examine the ongoing processes and evolution of planetary formation in the system. A protoplanet was identified in 2016 and that had increased the interest in that protoplanetary disk. In 2017, a shadow was identified that indicated the presence of an internal disk inclined relative to the external disk. Now a second shadow appears to come from another disk on the system’s inner side. This means that there may also be another planet in the making.
About 175 light-years away from Earth, the star TW Hydrae is a bit smaller than the Sun and is estimated to be only about 10 million years old. It’s still completing its formation and the disk of materials that surrounds it makes it particularly interesting.
A multi-year program aimed at tracking shadows in circumstellar disks that could reveal the presence of protoplanets included the TW Hydrae system. On June 6, 2021, observations conducted with the Hubble Space Telescope made it possible to identify a second shadow in addition to the one already known in previous years. The most likely explanation is that it’s inside the known one inclined relative to it with the consequence that it generates a new shadow. This indicates that there were detectable changes in the system in recent years.
The image (NASA, ESA, STScI, John Debes (AURA/STScI for ESA). Elaboration: Joseph DePasquale (STScI)) shows images of the TW Hydrae system captured with the Hubble Space Telescope’s Space Telescope Imaging Spectrograph (STIS) about 5 years apart. On the left side, the protoplanetary disk in 2016 is shown with a single shadow (A). On the right side, the disk in 2021 is shown with the already known shadow, here marked as (B), and the new shadow (C) generated by an inner disk.
According to the researchers, the two disks are probably misaligned due to the gravitational attraction of two protoplanets that are forming in two slightly different orbital planes. Just a few years ago, the two disks were so close that they cast no shadows but have drifted apart over time. John Debes of AURA/STSc at ESA, lead author of this study, compared the two protoplanets to two racing cars that are close together but one slowly overtakes and laps the other.
Over the years, several hypotheses were offered regarding possible protoplanets forming in the TW Hydrae system. The dramatic growth of knowledge in the field of exoplanets improved the techniques for detecting exoplanet candidates and their verification. However, in the case of protoplanetary disks, it remains difficult to verify their existence due to the considerable presence of gas and dust. Protoplanets close to their star are even harder to spot due to the strong starlight. For these reasons, it’s still difficult to determine how many planets are forming in the TW Hydrae system.
Previous studies had already made the TW Hydrae system interesting for observations to be conducted with the James Webb Space Telescope, whose infrared sensitivity could be a significant aid in examining the multiple protoplanetary disks of TW Hydrae. Surely, in the coming years, we will know more about a system that could be similar to the primordial solar system.
