Beta Pictoris is a violently exciting extrasolar system and now we have fresh new models investigating just what is happening in the collisions and chaos. The model of debris, disk, warps, waves, and rings tracks the evolution of the system over millions of years, and is downright gorgeous.
Three-dimensional model of dust distribution in the Beta Pictoris system. Image credit: NASA Goddard Scientific Visualization Studio extracted by Mika McKinnon
Astronomers Erika Nesvold and Marc Kuchner paired up to make a three-dimensional particle model of the Beta Pictoris system, where each particle represents a cluster of smaller bodies that have the same motions. The behaviours of these particles over the simulated millennia allow the researchers to track how collisions produce dust and interact to make the mysterious clumping observed by telescopes.
Beta Pictoris is a fantastic target in part because it’s so close to us at just 63 light years away. The system itself is quite young: at an estimated 21 million years old, the system was just getting started when mammoths roamed the Earth. Its youth means it still has an active disk of debris with endless collisions as rock and ice accrete into planets or grind into ever-finer fragments. The disk contains a number of odd features: a second, faint disk of dust inclined to the first creates an X-shaped pattern, the debris disk has odd warps, and it has massive clumps of carbon monoxide. It also has the more standard grading we expect in a disk, where the largest fragments have been cleared out closest to the star.
Observed [top] and modelled [bottom] dust distribution in the Beta Pictoris system. Image credit: ASA/ESA/D. Golimowski/NASA Goddard/E. Nesvold/M. Kuchner
Previous theories to explain the unusual disk features were either corralling from a yet-to-be-observed additional planet, or relic features from a not-so-distant collision between massive, Mars-sized icy comets. But now with the new model, Kuchner exults that everything makes sense without adding complexity:
Our simulation suggests many of these features can be readily explained by a pair of colliding spiral waves excited in the disk by the motion and gravity of Beta Pictoris b. Much like someone doing a cannonball in a swimming pool, the planet drove huge changes in the debris disk once it reached its present orbit.
The most important finding from the model was how much influence Beta Pictoris b has on shaping its system. Beta Pictoris b is an exoplanet roughly nine times the mass of Jupiter and in an orbit roughly equivalent to Saturn’s, taking 20 years to make a single orbit around its sun. It’s a popular target for exoplanetary studies: it was the first exoplanet to be directly imaged, and the first exoplanet where we calculated the length of a single day.
Cut-away revealing waves and clumping in the Beta Pictoris debris disk. Visualization credit: NASA Goddard Scientific Visualization Studio
The planet’s tilted eccentric orbit drags it through the particle disk twice an orbit at variable distances from its home star, inducing a vertical spiral wave precessing across the face of the disk. The result is a concentration of debris in crests in troughs where collisions are more frequent, with more collisions closest to the star that grind larger fragments ever-smaller.
Watch the full story of the model here:
By modelling superparticles of clumps of similarly-behaving bodies, researchers were able to greatly reduce the total number of particles and boost model efficiency. The Superparticle-Method Algorithm for Collisions in Kuiper belts (SMACK) technique still required 11 days of time on NASA’s Discover supercomputer to track how all 100,000 superparticles interacted over the disk’s lifetime.
The model can’t answer everything. In a press release discussing the results, Nesvold explains:
One of the nagging questions about Beta Pictoris is how the planet ended up in such an odd orbit. Our simulation suggests it arrived there about 10 million years ago, possibly after interacting with other planets orbiting the star that we haven’t detected yet.
You can help astronomers identify more debris disks around distant stars, adding to the catalogue of sample systems that scientists use to understand the evolution of young star systems and the formation of their exoplanets.