How did the sun wind up in the middle of the solar system? Did the materials, gas and dust that eventually formed the planets come from the sun?
Since our solar system is already formed, we must try to reconstruct its history by studying current star formation in our local neighborhood, the Milky Way galaxy.
To understand how the sun ended up in the middle of the solar system, we need to consider the process of star and planet formation. The materials that eventually formed the planets, including gas and dust, did not come directly from the sun. Instead, they originated from a large molecular cloud in our galaxy.
Here's an overview of the steps involved in the formation of the sun and the solar system:
1. Molecular Cloud: Stars form within vast clouds of gas and dust called molecular clouds. These clouds consist of mainly hydrogen and helium, along with trace amounts of heavier elements.
2. Stellar Nursery: Within the molecular cloud, regions of higher density, known as stellar nurseries or protostellar nebulae, start to collapse under the influence of gravity. The collapse could be triggered by various factors, such as the shockwave from a nearby supernova or the compression by a passing cloud.
3. Protostar Formation: As the cloud collapses, it fragments into smaller clumps. One of these clumps becomes the protostellar core, also known as a pre-stellar or proto-solar nebula. The core begins to contract and heats up due to gravitational energy conversion.
4. Accretion Disk: As the core contracts, it forms an accretion disk around the central protostar. This disk is composed of gas and dust that has fallen inward under gravity. The disk is spinning and has a flattened shape.
5. Planetesimal Formation: Within the protoplanetary disk, tiny particles of dust and ice start to collide and stick together, forming larger clumps called planetesimals. These planetesimals continue to collide and grow into proto-planets.
6. Formation of the Sun: In the center of the protoplanetary disk, the protostar, which is now the Sun-to-be, continues to accrete mass from the surrounding disk. Eventually, the central protostar reaches a critical mass and undergoes nuclear fusion, igniting as a star.
7. Planet Formation: As the protoplanetary disk evolves, the continuing collisions and accretion among planetesimals lead to the formation of planets. Through a process known as planetary accretion, dust and gas accumulate into larger bodies, eventually forming the rocky planets like Earth and the gas giants like Jupiter.
It's important to note that the formation of the solar system is still an active area of research, and scientists continue to refine our understanding through observations, simulations, and studying other star systems.