Rotating Disk Could Contain Newly Forming Planets

Astronomers from the University of St. Andrews have found evidence that a ring of dust around nearby Epsilon Eridani is rotating. The observations were made using the Submillimetre Common User Bolometer Array (SCUBA), which images the sky in the near infrared spectrum. This gives evidence to the theory that the disks of gas we see around newborn stars will eventually go on to become planets. In fact, the clumps of material tracked by the astronomers could even be newly forming planets themselves, still embedded in a vast disk of gas and dust.

Astronomers theorize that stars and planets form from clouds of dust and gas that gather together through mutual gravitational attraction. As the material falls inward, the random movements of particles average out, and the whole cloud begins to spin, eventually flattening out like a spinning pizza dough.

The centre of the protoplanetary disk eventually gains enough mass to ignite as a star. Out in the disk, particles of dust clump together, forming larger and large rocks, asteroids, and eventually planets. The newly ignited star creates a powerful stellar wind that clears out the dust from the system – you’re left with a solar system. This whole process, from start to finish is thought to take between 10 and 100 million years to finish.

At least, that’s the theory. And the disks seen around several newly forming stars help accumulate the evidence. But astronomers are skeptical, always looking for more evidence to lead credence to the theory or discount it.

In a recent paper entitled Detecting a Rotation in the Epsilon Eridani Debris Disc, astronomers from the University of St. Andrews discuss how they’ve tracked the rotation of a protoplanetary disk around Epsilon Eridani.

The observations were made using the Submillimetre Common User Bolometer Array (SCUBA). This revolutionary instrument is connected to the 15-metre James Clerk Maxwell Telescope, and is the largest instrument in the world that can detect submillimeter radiation. It was retired from service in 2005; however, a sequel, SCUBA-2 will be deployed in 2007.

The disk was first analyzed by the array in 1997-1998, and then again between 2000-2002. Over the course of this timeframe, clumps of material appear to have rotated counter-clockwise around the central star at a rate of 2.75 degrees a year (they would complete an orbit every 130 years).

The rate of motion of these clumps matches the theory that the ring around Epsilon Eridani is in fact a protoplanetary disk. These clumps in the disk might actually be new protoplanets, gathering material from the disk. If they were located in our Solar System, these planets would be a little further out than Pluto.

These observations were made at the limits of SCUBA’s sensitivity. The astronomers are hoping that future observations with SCUBA-2 will be able to confirm these findings, and get a better look at these newly forming planets.

Written by Fraser Cain