When planetesimals collide with each other, various outcomes can occur depending on the nature of the collision and the material involved:
1. A planet is formed: When planetesimals collide and merge together, they can gradually accumulate mass and eventually form a larger celestial body, such as a planet. This process, known as accretion, is a key mechanism in the formation of planets within a developing solar system.
2. A star is formed: While planetesimals themselves do not directly form stars, collisions between planetesimals in a protoplanetary disk can lead to the eventual formation of a star. The intense gravitational forces and material interactions within these disks can trigger the process of stellar formation, culminating in the birth of a new star.
3. A galaxy is formed: The collision of planetesimals is not directly responsible for the formation of galaxies. Galaxies are vast systems of stars, gas, dust, and dark matter held together by gravity. They typically form through the merging of smaller galaxies or the gravitational collapse of large clouds of gas and dust over cosmic timescales.
In summary, when planetesimals collide with each other, they can contribute to the formation of planets through accretion or participate in the complex processes that lead to the birth of stars within protoplanetary disks. However, the formation of galaxies involves much larger scales and processes beyond individual planetesimal collisions.
