A New Realistic Model Shows How Planets Form In Binary Star Systems

Astronomers have developed what they say is the most realistic model so far of planet formation occurring in binary star systems. The researchers on the project are from the University of Cambridge and the Max Planck Institute for Extra-terrestrial Physics. The study investigated a type of binary system where the smaller companion star orbits the larger parent star about once every 100 years.

The nearest star to the sun, Alpha Centauri, is an example of this type of star system. If our solar system were a binary system such as Alpha Centauri, it would have a second sun orbiting where Uranus is. For planets to form in this type of binary star system, the planetesimals, which are planetary building blocks orbiting a young star, have to start off at a size of at least 10 kilometers in diameter.

Researchers also found that the disk of dust and ice and gases surrounding the star where the planets form needs to be relatively circular. The research brings the study of planet formation in binary systems to a new level of realism and explains how planets in the systems could've formed. Astronomers believe that planet formation begins in a protoplanetary disc consisting primarily of hydrogen, helium, and tiny particles of ice and dust that orbit a young star.

The current leading theory on how planets form is known as core accretion. Under that theory, dust particles stick to each other, eventually forming larger and larger solid bodies. If the process stops early, the result can be a rocky Earth-like planet. However, if the planet grows larger than Earth, its gravity is sufficient to trap a large quantity of gas from the disk leading to the formation of a gas giant like Jupiter. However, planet formation in binary systems is more complicated.

The new research developed a detailed mathematical model of planetary growth in a binary system using realistic physical inputs and took into account processes typically overlooked. Those often overlooked processes included the gravitational effect of the gas on the disk and the motion of planetesimals inside it. The model found that planets can form in binary systems assuming the planetesimals start at least 10 kilometers in size and the protoplanetary disc is circular.