Origin of the Chemical Elements Flashcards
Evidence to support the Big Bang Theory
- Red shift
- CMBR
Initial Elemental Composition of Universe
- 75% Hydrogen
- 25% Helium
- Small quantities of light elements e.g. lithium
Life cycle of the sun (a yellow star) starting as a nebula
Nebula, Yellow Star, Red Giant Star, Planetary Nebula
Life cycle of a blue star starting as a nebula
Nebula, Blue Star, Red Supergiant, Supernova explosion, Black hole or Neutron star
A main sequence star spends most of its lifetime…
Undergoing nuclear fusion of hydrogen into helium
Brown dwarf stars are failed stars because…
They haven’t got enough mass to get hot enough to achieve nuclear fusion
Red dwarf stars are…
Main sequence stars. They are low mass and achieve nuclear fusion. Not very bright and have long lifetimes
Red supergiant stars are formed from massive main sequence stars at end of their lifetime. What happens when they run out of helium?
Collapse quickly to produce giant explosion known as supernova forming elements heavier than iron
What happens to low mass supergiant stars?
From nebulae where new stars start to form again
What happens to high mass supergiant stars?
From neutron stars where core has collapsed
What happens when very high mass supergiant stars collapse?
Becomes a black hole
2 forces acting inside a star
- Inward force of gravity
- Outward force of combination of gas and radiation pressure
What is gas pressure caused by?
Rapid random motion of particles in sun
What is radiation pressure caused by?
Light hitting the particles
What will happen to star if pressure in middle falls?
Shrink. Pressure will then rise once more until new equilibrium established with smaller star
If pressure increases, the star will…
Expand
Main sequence stars fuse what in their cores?
Hydrogen and Helium
End of main sequence stage our sun will…
QWC
- Run out of light elements (hydrogen and helium) to fuse
- Nuclear reactions stop, pressure drops
- Nucleus shrinks, density and temperature increases allowing heavier elements to fuse
- Lighter elements fuse in shell around nucleus
- Stars like our sun don’t reach temperatures to fuse elements heavier than oxygen
- Outer layers of star pushed off by radiation pressure of core, enriching interstellar medium with heavier elements
- Dense core remains as white dwarf
Stars heavier than our sun…
Have shorter lifetimes as they use their fuel up more quickly
2 important things that happen when supernova explosion occurs
- Elements blasted into space to form new stars
- Material heated to billions of degrees, fusing to form heavier elements (uranium)
The higher the binding energy per nucleon…..
The more stable the nuclei are
What happens to heavier elements when they fuse?
Absorb energy
What is nuclear fission?
Decay process where unstable nucleus splits into 2 fragments of comparable mass
(Split heavy nucleus into 2 lighter nuclei)
Sir Fred Hoyle and others used experimental results to:
- Show how heavy elements could be produced
- Explain why some elements were more common than others e.g. Carbon and Oxygen
What is nucleosynthesis?
Elements heavier than Helium produced in stars
What is nucleosynthesis limited by?
Initial mass of main sequence star
Scientist that described the process nucleosynthesis
Sir Fred Hoyle
