Giant gap in disk around Sun-like star suggests presence of multiple planets
Using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO), a large international team of astronomers has observed and examined PDS 70, a young star about 10 million years old with a mass similar to that of the Sun.
Images captured from the observations clearly show a giant gap inside the protoplanetary disk, the largest ever found among lower mass stars similar to the Sun.
The researchers think that the gap in PDS 70's protoplanetary disk may have resulted from the birth of multiple planets because no single planet, regardless of how heavy or efficient it is in its formation, is sufficient to create such a giant gap.
The high contrast images from the observations allowed the researchers to study the details of the disk, which then enabled them to directly reveal the site of formation of one and possibly more planets.
The team led by Jun Hashimoto (National Astronomical Observatory of Japan) and Ruobing Dong (Princeton University) is now attempting to detect those planets.
The goal of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS, Note 2) Project, begun in 2009, is to study the disks around less massive stars like the Sun.
As part of the SEEDS Project, the current team chose to target PDS 70, which is located in the constellation Centaurus; is about 460 light years from Earth; and has a mass 90 percent that of the Sun. Estimated to be about 10 million years old, this is a very young star relative to the 10 billion year life span of Sun-like stars and the 4.6 billion year age of our Sun.
Previous observations of the spectral energy distribution and direct imaging by the Very Large Telescope in Chile suggested the presence of a disk, but were not able to determine the details of its structure.
The observations with HiCIAO mounted on the Subaru Telescope clearly show a low-density space between PDS 70 and the inner edge of the disk surrounding it, with a radius as large as 70 astronomical units (AU, the distance between Earth and Sun
The huge size of the gap in the disk around PDS 70 led the team to question how the gap formed. By studying the details of the spectral energy distribution (plotting the brightness of light vs. wavelength) of the star itself and the disk, they found another disk at a distance of only 1 AU.
Gravitational forces from the planet(s) embedded in the disk might account for this kind of gap in the disk, because they could pull away the material from the disk, and the clearing of the material means less infrared radiation from that area. It would be very difficult for a single planet to create the giant gap in the disk around PDS 70.
The research team thinks that more than one planet could be responsible for creating the gap. However, conducting observations to detect such planets is difficult, because the scattered light from the disk can obscure the very faint light emitted from planets.
The high contrast images made possible by observations with HiCIAO revealed the surprising details of PDS 70's protoplanetary disk.
Team leader Jun Hashimoto (NAOJ) commented, "Thanks to the powerful combination of the Subaru Telescope and HiCIAO, we are able to probe the disks around Sun-like stars. PDS 70 shows how our solar system may have looked in its infancy."