ASTR 1514 1st Edition Lecture 12Formation of Proto-stellar Disks and PlanetsAngular Momentum – The quantity of rotation of a of a body, which is the product of its moment of intertia and its angular velocityConservation of angular momentum is similar to Newton’s first law (object in motion stays in motion unless acted upon by an external force), except applied to rotating objects. This force is called torque. - Nearly everything in the universe starts out with some angular momentum. - However, not enough torque to slow down a large object like a collapsing molecular cloud. Angular momentum of rotating body (Direct Relationships)- Depends on the mass of the rotating body. More Massive = More angular momentum - How fast it’s spinning. Spinning Faster = More angular momentum- Depends Radial Extension. More radially extended = More angular momentum Conservation of Angular Momentum means that there is no torque, so no change in angular momentum. Ex: If rotating molecular cloud is collapsing (small extent) it must compensate by spinning faster. Giant Molecular Clouds form- The small proto-star at center- An extended disk of dust and gas- A proto-star has most mass but it is small in comparison to a disk- Disk is less massive, but is extended. - Jupiter has larger angular momentum than the sun. Accretion disks are a natural consequence of conservation of angular momentum. Presence of an “infrared tail” in the spectrum while observing, implies the presence of a disk. Formation of Planets from proto-planetary Disks- Within the disk, particles are moving along together in orbit around the star.- Particles stick together to form larger particles. - Larger particles sweep up smaller particles that get in their way.- Collision may cause them to break apart.- But overall the particles are getting larger and larger. - Gravity may draw smaller particles onto larger particles. - Planetesimals – Larger aggregates more than 1 kilometer across. Planets can clear out all the material at their radius leaving the disk with gapsRemaining dust and gas is accreted into the star, or scattered out into the outer regions of the planetary system. Composition of PlanetsEvery type of matter has three phases – Solid, Liquid, and Gas. Ex: Water, Solid form is Ice, its liquid form is water, and its gaseous form is steam. But other materials also have the same 3 phases. Phases depend on Pressure and Temperature- Solid: Low temperature, Higher pressure- Gas: Low pressure, Higher TemperatureMelting Point: Transition from solid to liquidBoiling Point: Transition from liquid to gasMaterials Divided into two parts1. Refractory Materials – Capable of withstanding high temperatures without melting or being vaporized. Ex: Iron and Silicates. 2. Volatile Materials – Are in solid form only at very low temperature. Ex: Water, ammonia, methane. Proto-planetary disk is hotter when closer to the star (source of energy) and cooler when farther away. - Refractory Material condenses at all radii- Volatile Materials are in gas form closer to the star – and escapeSolar System Planets1. Planets closer to the sun are principally made of refractory materials, such as; Earth, Mars, Venus, Mercury. 2. Planets that are farther from the sun are principally made of volatile materials,with some refractory materials, such as; Jupiter, Saturn, Neptune,