Initial Stage:
* Low Temperature: The initial cloud is extremely cold, typically around 10 Kelvin (-441 degrees Fahrenheit).
* Low Luminosity: The cloud radiates very little energy, making it incredibly faint.
Collapse and Heating:
* Gravitational Potential Energy Conversion: As the cloud collapses under its own gravity, the gravitational potential energy is converted into kinetic energy. This makes the gas particles move faster, increasing the temperature.
* Rising Temperature: The temperature at the core of the collapsing cloud starts to rise significantly.
* Increasing Luminosity: The protostar becomes more luminous as it heats up and starts radiating energy.
Protostar Formation:
* Central Concentration: The majority of the mass gathers at the center, forming a dense, hot core.
* Accretion Disk: Material continues to fall onto the protostar, forming an accretion disk around it. This disk spins rapidly and is responsible for transporting material inward.
* Surface Temperature: The surface temperature of the protostar is still relatively low, typically around 1000-2000 Kelvin.
Towards Starhood:
* Continued Heating: The core continues to heat up due to ongoing accretion and gravitational compression.
* Fusion Ignition: Eventually, the core reaches a temperature and pressure high enough for nuclear fusion to begin.
* Stable Star: Once fusion ignites, the star becomes stable, balancing the inward force of gravity with the outward pressure from fusion.
In summary:
* Temperature: The surface temperature starts extremely low and increases gradually during the protostar phase. It will continue to rise significantly once fusion begins, leading to a stable, luminous star.
* Luminosity: The protostar's luminosity begins very low and steadily increases as it heats up. The luminosity will jump dramatically when fusion starts, signifying the birth of a true star.
Important Note: The exact temperature and luminosity evolution depends on the mass of the protostar and other factors like the composition of the initial cloud.
