Life of Stars


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This talks about stars- from how they are formed to the death of a star, from the nebula to the black hole.

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Life of Stars

  1. 1. Astronomy(Life of Stars)by Merlin Raphael Page 1
  2. 2. The UniverseScientists believe the universebegan in a “big bang”, about13,700 million years ago. Theuniverse continues to expandtoday. The evidence for the“big bang” theory includes theexistence of a microwavebackground radiation and redshift. The universe containsextremely dense objects andmay consist mostly of darkmatter that cannot be seen.Stars do not remain the same- they change as they age. Page 2
  3. 3. The Origin of StarsNebula: A large cloud of gas(helium and hydrogen) and dustwhich forms into a star.Dust and gas particles exert agravitational force on each otherwhich keeps pulling them closertogether.As the particles pull closer togetherthe temperature increases.At 10,000,000o C fusion takesplace and energy radiates outwardthrough the condensing ball of gas. Page 3
  4. 4. -Cloud Collapse - occurs deep in cloud-“EGGS” (EvaporatingGaseous Globules) :Dense regions forming newstars - surrounding gas &dust “eaten into” by strongstellar winds, UV photons &ionization fronts. Page 4
  5. 5. The StarA star is a luminous globe ofgas producing its own heatand light by nuclearreactions. They are bornfrom nebulae and consistmostly of hydrogen andhelium gas. Surfacetemperatures range from2000°C to above 30,000°C,and the correspondingcolours from red to blue-white. Page 5
  6. 6. Red GiantsAfter hydrogen is exhaustedin core, energy releasedfrom nuclear fusion counter-acts inward force of gravity.-Core collapses,•Kinetic energy of collapseis converted into heat.•This heat expands theouter layers.-There is an increase intemperature and pressureduring the collapse. Page 6
  7. 7. Planetary NebulaPlanetary nebulae are theouter layers of the star thatare lost when it changesfrom a red giant to a whitedwarf.After helium is exhausted,the core collapses and theouter layer of the star isexpelled. The outeratmosphere is ionized bythe hot remaining core. Page 7
  8. 8. White DwarfWhite dwarfs are theshrunken remains of normalstars whose nuclearsupplies have been usedup. They consist ofdegenerate matter with avery high density due togravitational effects.A white dwarf cools andfades over several billionyears. Page 8
  9. 9. SupernovaThis is the explosive death of astar. It often results in the starobtaining the brightness of 100million suns for a short time.Type1- These occur in binarystar systems in which gas fromone star falls onto a whitedwarf, causing it to explode.Type2- These occur inmassive stars, which sufferrunaway internal nuclearreactions at the end of theirlives. Page 9
  10. 10. Neutron StarsThese stars are composedmainly of neutrons and areproduced when a supernovaexplodes, forcing the protonsand electrons to combine toproduce a neutron star. It isvery dense. Typical stars havea mass of 3 times the sun, buta diameter of only 20km. If itsmass is any greater, it willshrink further to become ablack hole. Page 10
  11. 11. Black HolesThese are believed to formfrom massive stars at the endof their lifetime. Thegravitational pull in a blackhole is so great, nothing canescape from it- not even light.The density of matter in ablack hole cannot bemeasured. Black holes distortthe space around them, andcan often suck neighboringmatter into them, includingstars. Page 11
  12. 12. Page 12
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