Stellar Evolution

Stellar EvolutionStory of The very part of us

Here I Start!!- Molecular CloudsJourney of formation starts from molecular clouds containing H2 and He and traces of CO, NH3, H2CO , CS, N2H+ etc. - hence molecular clouds.

FRAGMENTATIONMolecular clouds are generally of the order 105x (solar mass)-This huge mass star so far has not been foundFragmentation process occurs causing fragmentation of molecular clouds in smaller masses each initiating its own process of star formation ( if conditions are met)

THERMODYNAMICS INSIDEAs the cloud collapses the gravitational energy is transformed to radiation and this goes out by collisional excitation of rotational levels of molecular hydrogen (0.1 eV) and infrared cooling by dust grains.Hence the collapse is isothermal.

Further the star collapses under gravitational influence and until the star becomes sufficiently opaque to prevent further radiation and ultimately radiate like black bodies.This process is adiabatic.

FUSION !!Further collapsing of star causes huge amount of heat generation, sufficient to initiate the process of Fusion of Hydrogen gas to Helium.

The Gigantic Disk The spiraling of dust around star causes formation of a gigantic disk called Protostellar DiskThe relative denser dust around forms planets though collision process.All this and more plays on a single physics formula CONSERVATION OF ANGULAR MOMENTUM.

MAIN SEQUENCE STARUnder the condition of Hydrostatic Equilibrium, i.e, outward Radiation Pressure is balanced by inward Gravitational Force.

Windows User (WU) - add pic showing hydrastatic eqmWindows User (WU) - add data of life spanTypes of Stars:

Our Sun is a Yellow Dwarf and a type G star

Windows User (WU) - Kinds of Stars we should knowStars very low in mass are called Red Dwarfs.Stars like our sun are called Yellow Dwarfs or Yellow Stars.Stars very huge in mass are called Blues Stars.Their colors are as per their names distributed as per Hot Body Energy Distribution.

Herchell Russell Diagram

Observations made on kinds of stars and their stages on Temperature vs. Luminosity.

Windows User (WU) - check spellingWindows User (WU) - use HD pic insteadQuestion for audienceWhich star do you think will have greater life span in comparison to their masses.Will star of greater mass live longer or the opposite??

AnswerAlthough it may seem counter intuitive, but stars of greater mass have comparatively shorter life span in comparison to stars lesser in mass.As more energy is required to be radiated out for stars like 0Blue Star, maintaining its luminosity though out its entire life span.For smaller stars like white lesser energy is required in a similar way.

THERES AN END TO EVERY STORYEventually star runs out of fuel.Star collapses further generating more and thus fusion of helium begins forming denser elements.This goes up to the formation of Uranium depending upon the mass of star.Outer envelope expands further as gravity loses control over it.

STAGES OF STAR UNTIL DEMISE

Windows User (WU) - pic of u know whatHow Do They End ??Every Star its own of ending highlighting the magnificence of the beauty of COSMOS.

Just radiates.Thats it !!Red Dwarfs being the smallest star live the longest.Throughout their life span they radiate energy.Finally end up when no more fuel is left and fade out.

Red Giant PhaseFor stars like our sun, they end up expanding their outer envelope.As for in our solar system this envelope has probabilistic reach up to Earths Orbit.

Super Nova- Type II AWith stars of mass > 1.4 x solar mass, they go super nova stated as Chandrashekhar Limit.Further collapse in stars is brought to halt by inside denser part ( neutrons in case of neutron stars).This creates shockwaves confronting outer incoming envelope.This causes an extreme burst of envelope in no time.Supernova explosions are so bright that it energy radiated in those 2-3 seconds are equivalent to energy radiated by star in its entire life span.During this explosion all the matter formed due to fusion gets thrown out into space and a very similar process injected matter in our solar system as well.

Windows User (WU) - insert videoWE ARE MADE OF STAR STUFF!!Every element inside us, every iron running in our blood and every calcium in our bones is from the insides of star

Gamma Ray BurstGamma Ray bursts are considered to be deadliest explosions of space.Shock Waves generated sometimes create intense magnetic field along poles.This accelerates electrons at very huge rate causing intense radiation emission particularly in order of gamma ray wavelength.

Windows User (WU) - inser mast picHyper NovaWith stars of very huge mass of order > 100 solar masses under hyper nova.Hyper Nova is a greater version of super nova.Presently in Eta Carina constellation a Huge Blue star of 150 solar mass is about to go Hyper Nova any minute or MAY BE RIGHT NOW !!

Windows User (WU) - see details from cosmos episode.Windows User (WU) - WHITE DWARFSFormed when collapsing stops at stage when the further collapse is stopped due to repulsion forces of electrons called Electron Degeneracy Pressure explicable through Paulis Exclusion principle.

NEUTRON STARSIn stars of greater mass further gravitational collapse pushes electrons into protons building up Neutron Degeneracy Pressure.

PULSARSNeutron stars carry along huge magnetic field and with its huge magnetic strength it accelerates electrons within it causing emission of radiation of various wavelengths.Since in some neutrons rotational axis is aligned along magnetic axis, the radiation seems emanated periodically just like Light-House.Pulsars are also called LIGHT HOUSE of cosmos.

BLACK HOLESStars very huge in mass of order > 10x solar mass, collapse beyond the star of neutron star forming ultra dense objects of space.These dense objects have so much gravitational influence that even light cannot escape from its pull.The dense point is called Singularity. Beyond this point so far every mathematical calculation has failed as translation starts taking place in time than in spatial coordinates.

SPACE BIZARRES DONT END UP HERE !!

BLUE STRAGGLERS

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Although our story of star formation till demise might have ended.But recent discoveries have shown mankind the most bizarre and perplexing nature of universe.

Binary StarsUnlike our sun, many of the stars in our galaxy have a companion star.Often one star goes under demise stage before the other forming white dwarf, neutron star or even a black hole.The companion dead star pulls away the material of other star accreting around it in form of a disk.This accretion process very often causes over heating leading to nuclear burst on its surface know as NOVA.SO DONT CONFUSE NOVA WITH SUPERNOVA !!

SUPER NOVA- TYPE I AThe accreting mass around dead star when finally reaches a critical stage of mass and no mass is added further, it goes supernova.Recently observed supernova in February was Type I A Supernova .

Windows User (WU) - see detailsWindows User (WU) - add latest picSuper Massive Black HolesGenerally found in the center of Spiral Galaxies This Black Holes are of mass of order million times massive than our Sun.

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