Proplanetary Disk Gaps Don't Always Signal Planets

Protoplanetary disks of gas and dust that surround young stars sometimes show dark gaps when viewed, which are often caused by unseen planets. However, a recent study found that protoplanetary disks do not always signal hidden planets, and the gaps could actually be cosmic illusions and not the sign of hidden planets after all.

"If we don't see light scattered from the disk, it doesn't necessarily mean that nothing is there," said Til Birnstiel, from Max Planck Institute for Astronomy in a news release. Birnstiel conducted the study while at the Harvard-Smithsonian Center for Astrophysics.

In their experiment, the researchers studied disks that shine in visible wavelengths due to reflected light. The scattered light derives from starlight, which is released from miniature-sized particles, similar to cigarette smoke.

Over time, these small particles gather together to form large objects, which eventually become giant planets. However, particles do not always form giant planets - sometimes they break apart instead of clinging together. The particles can either move closer to or farther away from a star, which is known as migration. The researchers used the Smithsonian's Hydra supercomputer cluster to examine the process.

"Growth, migration and destruction can have tangible, observable effects," said Sean Andrews, co-author of the study. "Specifically, these processes can create an apparent gap in the disk when the small particles that scatter light are cleared away, even though larger particles still remain."

In order to determine if a planetary disk is real, astronomers need to make observations at longer wavelengths of light that can pick up the pebbles, according to the researchers.

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