By Dave DeFusco
When we think of the solar system, we usually imagine the Sun, the planets and maybe the icy belt of comets far beyond Pluto. But according to Edward Belbruno, a Katz School mathematician and astrophysicist, the solar system is much bigger than that, stretching even toward the stars around us.
Belbruno explained this surprising idea in his keynote lecture at the prestigious Niels Bohr Colloquium, which closed the weeklong conference on astrophysics, cosmology and particle physics at the University of Copenhagen鈥檚 Niels Bohr Institute. The event, held in August, brought together some of the world鈥檚 leading scientists to discuss the biggest questions in physics in the very hall where quantum mechanics was born.
Belbruno鈥檚 talk, 鈥淧ermanent Capture into the Solar System and Moving about it Chaotically,鈥 used the mathematics of chaos theory together with the structure of our galaxy to show that the solar system has no sharp edge. Instead, its gravitational influence stretches outward and blends with the regions around nearby stars.
鈥淵ou could think of it as overlapping neighborhoods,鈥 said Belbruno. 鈥淭he Sun鈥檚 neighborhood reaches farther than we once believed and it touches the neighborhoods of other stars.鈥
One of the key ideas comes from chaos theory, which studies how small changes can lead to unpredictable paths, like a leaf carried by swirling wind. Belbruno applied this to the way objects move under the pull of gravity. He showed that objects from interstellar space, such as rogue planets or even small black holes, might not simply pass through our solar system but could actually be captured by it. These captures would happen in complicated, chaotic ways, but once caught, the objects could become permanent members of our cosmic family.
This changes how we think about the solar system itself. Instead of being a closed system with nine planets and a cloud of comets, it may be an open system, constantly interacting with the wider galaxy. That means the solar system could occasionally collect exotic visitors drifting between the stars. Some of these visitors might be harmless chunks of rock and ice; others could be massive rogue planets that were thrown out of their original systems. In extreme cases, there is even the possibility of tiny black holes being drawn in.
For Belbruno, being invited to deliver the keynote lecture at such a historic and distinguished conference was a deep honor. 鈥淭o speak in the very place where Niels Bohr and his colleagues laid the foundations of modern physics and to share these new ideas with today鈥檚 leading scientists was an extraordinary experience,鈥 he said.
