The red line shows the evolutionary track of a simulated planet that finally has similar properties as the actual planet TOI-849b, as found in the Bern Model of planet formation and evolution. The track is shown in the plane of semimajor axis in astronomical units (AU), that is the orbital distance from the star, on the x-axis, and the radius of the planet in units of jovian radii on the y-axis. The blue-red points show other planets predicted by the model. The Earth and Jupiter are shown at their positions for comparison.
The planet starts to form at the initial time t=0 years as a small planetary embryo at about 6 AU. The protoplanet grows in mass in the following 1 million year which increases its radius. In this phase, the radius of the planet is still very large, as it is embedded in the protoplanetary disk in which it forms. The increasing mass of the protoplanet causes it to migrate inwards, towards the star. This reduces again the size of the planet. After 3.5 million years, the planet has migrated to the inner edge of the disk. There, it suffers a very energetic giant impact with another protoplanet in its planetary system. The enormous heat liberated in the collision strongly inflates the gaseous envelope of the planet. The envelope is lost via Roche-lobe overflow, and an exposed planetary core comes into existence.
In the following billions of years, the exposed core slowly spirals towards its host star because of tidal interactions. The simulate planet now has properties like a mass, radius, and orbital distance which are very similar the observed properties of TOI-849b that is shown by a black-yellow symbol. In the end, after about 9.5 billion years, the planet falls into its host star.