A team of British astronomers observing the long-known star DG Tauri have made an exciting discovery: when they brought the star’s thick dust cloud into focus, they found that it was made of pebble-sized rocks. This makes the cloud around DG Tauri the best look yet at a planetary system in the mid-stages of formation. It’s not a totally amorphous dust-cloud, nor a network of large and rarely interacting proto-planets. This is a thick, orbiting cloud of tiny rocks — and as the team brings in more data about its nature, the sheer chaos of that situation will hopefully become more clear.
The broadly accepted theory of planetary formation is that as stars form, they gravitationally attract small particles from surrounding space. Most of these fall straight into the star and add to its mass, but some have the correct angle and velocity to become trapped in orbit — and once the population of such particles becomes thick enough, the cloud can start to knock more and more incoming particles into a semi-stable orbit. As these particles randomly collide, they start to stick together, forming larger and larger aggregates. Once these “planetesimals” get to about 1 kilometer in size, they produce a strong enough gravitational attraction to start powering the clumping process on their own. That’s when the process of planetary formation really gets going, and the largest bodies start to carve the cloud into discrete circular bands.
So, finding a cloud of pre-planetary pebbles is actually quite important, because it illuminates a state between huge, gaseous clouds and the aforementioned banded pre-planetary systems. This study has found a star in the intermediate stages of planetary development. The dust-aggregation theory was already uniformly believed by astronomers, so this isn’t an unexpected discovery, but it’s a powerful confirmation. It’s also a reminder of just how much of modern astronomy, especially planetary astronomy, is only just now getting direct confirmation. Don’t forget that scientists only directly proved that there really were any planets outside of our own solar system in 1992, and were only able to start routinely cataloging them in the last 3-5 years.
DG Tauri wasn’t chosen at random. As NASA reported back in 2009, the star has a jet of hot gas exploding out at a right angle to its thick orbiting cloud of debris. University of Manchester’s Dr. Anita Richards calls such a jet “a beacon for stars still in the process of forming.”
These early observations couldn’t offer this level of detail, however, and this observation was only possible thanks to the eMERLIN array of radio-telescopes, which spans England and incorporates five different major dishes. These observatories capture the same astronomical from object across a country, allowing them to capture images at incredible resolutions. The data all gets transferred to Jodrell Bank Observatory for crunching into the final meta-observation
For years astronomers had to throw away the majority of the detail collected by the MERLIN array, simply because transferring it to the central node took too long over old-world data infrastructure. With the “e” upgrade to the original MERLIN array, fiber-optic cable is letting them put a much larger proportion of the data it collects towards actual scientific discovery.
Keeping with the tradition of rapid advancement in planetary science, eMERLIN is actually still in the process of being upgraded, and still has the potential for another four-fold increase in radio bandwidth. The team says that if they’ve already managed to find a cloud with pebble-sized particles, after the upgrade they’re likely to find a “whole zoo” of such clouds around other stars. And with some ability to tell what a “normal” intermediate stage of planetary development might look like, scientists should be able to come to a better understanding of how our own solar system formed — and at precisely what sort of rate.
