Question

Tell the life story of a 0.8Msun white dwarf from its humble beginnings as a main sequence star to its end as a white dwarf.

Answer 1

There are mainly & stages in a Star's life:

• Gas Cloud : the star intially begins as a cloud of gas and the temperature is cool enough for molecules to form, thus hydrogen molecules finds its way and are formed.
• Protostar: the molecules thus formed now start to collide with each other and as a result warms up the cloud. these warm collection of gases/molecules are called as a Protostar and since its warmer it can be seen in infrared vision.
• T-Tauri stage: in this stage the strong winds starts to blow in the young star which pushes the gases and molecules apart. This stage is visible without the aid of infrared or radio waves.
• Main sequence Stars: This is the stage where the young star finds equilibrium between the gravitational compression and the outward pressure. The star will spend 90% of its lifetime in this stage performing fusion reactions. The hydrogen fuses to form helium in this stage, produsing lots of energy in the form of heat and light.
• Red Giant: when the hydorgen fuel is fully converted into helium then the core collapses and the star expands. the mass of the star increases, the outer surface is now cooler than the main sequence star. the star first reaches the sub-giant stage and then after further expansion it becomes a red giant. if a star has exceptionally high mass then the star is called as a supergiant.
• Formation of heavy elements: The helium molecules now fuse to form carbon atoms, and this fusion reaction then keeps the core from collapsing, once helium fuel is over, then the star further expands and now carbon fusion into higher elements begings in the core. this process continues until iron is formed, when iron fuses it consumes the entire energy of the star thus the core finally collapses and prevents further fusion, massive stars collapse rigorously and create supernovae while smaller stars like sun form white dwarfs, while the outer shells radiate away as planetary nebulae.
• Supernovae, White Dwarfs and Planetary Nebulae: When the massive stars collapse, most of the star's mass is blown out in space, and the core implodes into a neutron star or a singularity ( Black Hole). while the less massive stars form white dwarfs out of their core and for stars less massive than the sun, red dwarfs are formed which can continue to glow for about trillions of years.