The wild lives of aging stars (and planets): leaving home, changing partners and participating in violent clashes

Through theoretical analysis and computer simulations, scientists from the Technion and the University of Boulder, Colorado have shown that the development of stars and planets in systems with three bodies may lead to surprising results; Stars and planets orbiting one star may change their orbits

Through theoretical analysis and computer simulations, scientists from the Technion and the University of Boulder, Colorado have shown that the development of stars and planets in systems with three bodies may lead to surprising results; Stars and planets revolving around one star may change their course and "jump" to another star, in most cases they may collide with the host star or the star they jumped to, and in other cases they may escape the system completely. In fact, this process may describe the wild history of the brightest star in the sky, aka Sirius. These findings raise the possibility that interstellar collisions are much more common (at least 30 times) than previously thought.

Most stars live alone, without a partner, or they share their lives with a single co-star. However, about 15% of all stars have at least two partners, forming together with them a triple system. A planet (planet) can also be "hosted" in a binary system - a system with two stars, thus it (the planet) becomes a component of a ternary system. The evolution of stars in such systems may lead to dramatic results. The aging of stars involves several major changes: a star can expand to a diameter hundreds of meters from its original size, then lose most of its mass in strong winds and end its life leaving only a core, a white dwarf (or end its life by exploding, then leaving behind a neutron star or hole black). The evolution of individual stars has been studied extensively in the last hundred years, and the evolution of binary stars - a system in which the two stars can "exchange materials" between them - has been studied for decades; In contrast, the evolution of triple stars has hardly been studied.

In the recent studies of Professor Hagi Peretz from the Technion Physics Faculty and Dr. Caitlin Crater from the University of Boulder, Colorado, ternary systems and their development deserve more attention. "Single-star and binary systems are stable systems, as a rule," says Professor Peretz. "Tripartite systems, on the other hand, are much more fragile, and in certain ternary systems, even a tiny change in the system may lead to an unstable configuration, which leads to chaotic and wild dynamic development, which occurs in a relatively short time."

The researchers discovered that the mass subtracted from one of the three components in the trio with their aging may lead to a significant change in the orbits of the three components around each other. Many such systems become unstable, and the three stars may get caught up in a wild dynamic dance, where the stars may switch partners until one of them is ejected from the system. However, since the mass-losing star usually swells at this stage, and its size is multiplied by hundreds of meters, it becomes a large target, which significantly increases its chances of colliding with another star during the wild "dance". "Usually, stars collide only in the dense environment of star clusters (systems in which millions of stars fill a volume of only a few light years; for comparison, in the same volume of space around our solar system there is only one star - the Sun) where two stars are not related to each other may collide by chance. Even in such dense areas the probability of such a collision is very low, and in most of the galaxy where the density is much lower, it can be said that such accidental collisions do not happen at all."
"We discovered that when it comes to triangular systems, the picture is completely different. Collisions between stars outside dense star clusters may occur at a rate 30 times higher than the cold random collisions within clusters.”

The strange case of the dog at night, and the solution to the riddle of the shining star in the sky - the researchers also discovered that such a triple development may be relevant to one of the most famous stars, Sirius - the brightest star in the sky, also known as the dog star. Sirius is accompanied by a white dwarf in a binary system, but in a highly elliptical orbit. This is an unusual configuration when it comes to a binary system whose one component is a close white dwarf; In such systems we expect a much more circular orbit, as a result of the transfer of mass from one star to its partner during the aging of the system. The latest research shows that this strange configuration can be explained if the binary system of Sirius was once a ternary system that evolved, became unstable, and one of its three components was thrown out of the system; A move that turned it into a binary system with an unusual trajectory. "The surprising realization that the triple evolution scenario we've been investigating may also solve a decades-old puzzle, relevant even to the bright star in our night sky, Sirius, is very exciting; It seems that Sirius had a much wilder history than we once imagined," says Professor Peretz.

Planets jumping between stars - what would you do if the neighborhood you lived in started to deteriorate? Would you consider leaving for a better neighborhood? It turns out that a similar thing may happen in planetary systems. Dr. Crater and Professor Peretz also examined systems in which one of the three components is not a star but a planet - a planet. "When the developing star has a close planetary partner and a distant planetary partner, the results can be very surprising," says Dr. Crater. "A planet can deviate from its original orbit around the host star, and start orbiting the other star. Such a 'star-hopper' may jump many times between the original host and the other partner, and finally settle on a stable orbit around the partner. It can remain in the new environment until the end of its life, or at least until the companion star begins to lose material as well. Borrowing, one could say that when the immediate neighborhood becomes uncomfortable, the planet jumps to another neighborhood…” However, this story sometimes has a worse ending for the planet, as it may collide with the distant star or the original host during these exchange of pairs, and thus be destroyed rather than found "Sympathetic" environment.