Stellar Evolution From protostars to supernovas
Protostars • Large nebulas of gas that begin to collapse or contract heat up as atoms interact, causing them to glow. • Once an opaque structure forms, it is considered a protostar.
Protostar Structure • As a protostar collapses, an accretion disk forms around the protostar, and jets of electromagnetic radiation erupt from the poles. • Jet • Accretion Disk
Brown Dwarf • When a protostar doesn’t have enough mass to cause large scale hydrogen fusion, it forms a small Brown Dwarf star. • Brown Dwarfs glow dimly, and are only a little bit larger than some planets.
Red Dwarf • A Red Dwarf is less than half a solar mass. • It has convection currents in its core and envelope. • It is relatively cool and dim. • They are the most common stars that are visible.
Sun-like stars • Sun like stars are similar in mass to our Sun. • The sun is a yellow dwarf star. • It has several layers.
Corona • Corona – The outermost layer, it is the second hottest at 4000 K. It is made of gases moving away from the sun, also known as the solar wind.
Chromosphere • The second layer of the sun. • The chromosphere is the thin lower layer of the atmosphere. • Solar flares and prominencesoriginate in the chromosphere.
Photosphere • The gaseous surface of the sun. • The photosphere absorbs heat energy from lower layers, and then releases the energy as light (electromagnetic energy.) • It is the part of the sun that visibly glows. • Cooler areas in the photosphere are darker, and are called sunspots.
Convection Layer • The next layer absorbs light and heat from below. • As it warms, convection currents are created that transfer heat from the inner layers to the photosphere.
Radiative layer • The radiative layer is extremely dense. • Electromagnetic x-rays are absorbed from the core, re-emitted, and reabsorbed. • It takes light millions of years to work its way through the radiative layer.
The core • The core is under such intense pressure from the layers pressing from above due to gravity. • The pressure is sufficient to cause nuclear fusion. • This releases tremendous amounts of energy as gamma ray electromagnetic radiation. • The outward force from fusion reactions keeps gravity from further collapsing the star. • The inward pressure from gravity keeps the fusion reactions from exploding the star.
Red Giants • These are stars that are between 0.3 to 6 solar masses. • Red giants form when all the hydrogen in a star’s core has fused to make helium. At this point, fusion stops, and gravity becomes the dominant force. • As the core contracts due to gravity, it heats up, releasing more energy to the radiative layer.
Red Giants 2 • As the radiative layer absorbs energy from the collapsing core, it also heats up until the pressure is enough to start hydrogen fusion in the outer layers. • The outward pressure from energy released by fusion in the outer layers causes the star to expand, causing it to grow to as much as 200 times larger.
White dwarf • White dwarves form when a Red Giant fuses the last of its hydrogen in its outer layers. • The outer layers heat up and expand to form a planetary nebula, which slowly drifts apart. • The inner core is left, slowly cooling and becoming darker until it forms a Black Dwarf.
Supernovas: Type 1a • If a white dwarf star absorbs enough new matter, its mass can increase enough to allow gravity to cause the heavy elements in the core to begin fusion. • Sometimes the resulting energy release is then enough to blow the star apart in a massive explosion.
Blue Supergiants • Blue supergiants are extremely hot and extremely dense. • They have enough gravity to fuse heavier elements such as Helium and Lithium to make elements as heavy as Iron. • They have very short lifespans before they fuse all the elements they can.