Transcript Birth of the Universe

no light!
Birth of the
Universe
Once upon a time, there was nothing, and then…
Age
What Was Happening
0☻
The “Big Bang”- a cataclysmic event in which
space, time and matter were effectively born from
a point-like source of pure energy. (To date,
physics can only explain events after 10-43 sec!)
The universe was grapefruit-sized; some matter
had appeared, but it was in an “unconventional”
form (quarks, leptons etc); the temperature was
1027 K.
10-35 sec
still
no light!
Birth of the
Universe
Age
What Was Happening
10-6 sec
The first “conventional” matter had
appeared (electrons, neutrinos and their
anti-particles); the temperature was 1013 K.
All matter was in “conventional” form
(including protons and neutrons); no atoms
had yet formed; the temperature was
1010 K.
Some atomic nuclei had “fused” (deuterium,
helium-3 and helium-4); there were still no
atoms; the temperature was 109 K.
2 sec
3 min
still
no light!
Birth of the
Universe
Age
What Was Happening
106 yrs
Nuclei and electrons had combined to form
atoms of hydrogen, deuterium, helium-3 and
helium-4; the universe was an expanding
cloud of gas (roughly 92% hydrogen, 8%
helium); the temperature was 3000 K.
Due to gravity, “clumps” had begun to form
within the expanding gas cloud; these would
continue contracting to become the first
stars!
107 yrs
Stellar Evolution
During the first 10 – 100 million years:
 A hydrogen/helium gas clump contracts under gravity to form
a dense spinning ball (often surrounded by a rotating disc of
gas and dust).
 Pressure and temperature in the core increase until, at about
10 million K, the core ignites and the star begins to “shine”.
During the next 1 – 10 billion years:
 There follows a long, stable period of hydrogen fusion into
helium, with inward gravity and outward pressure continuing
in perfect equilibrium.
 The larger the star is, the shorter the duration of this period.
 Our Sun is a small star, roughly halfway through this stage.
Stellar Evolution
During the next 10 – 100 million years:
 Depletion of hydrogen in the core causes a slight shrinkage.
 Helium begins fusing into carbon (and carbon into heavier
elements), driving up the core pressure.
 The star expands into a “red giant”.
 In the case of our Sun, this expansion will swallow the Earth!
During the final 1 week – 1 million years:
 When fusion into iron commences in the core, the star begins
consuming energy much faster than it can produce it.
 The core pressure drops steadily and the unstable star begins
to “collapse” under gravity.
 The star is dying, and its final “death state” depends on its size.
Stellar Evolution
Final Death States of a Star:
 A small star (like our Sun) shrinks slowly to a tiny, dense “white
dwarf”, eventually cooling to a “black dwarf cinder”.
 A large star undergoes a rapid, catastrophic collapse, in which
the core collapses faster than the outer envelope.
 The sudden increase in core pressure produces a “supernova”
explosion which blows the stellar envelope and most of the core
away.
 The remainder of the original core continues to collapse, ending
up either as a “neutron star” or a “black hole”.
 Since iron is the heaviest element created in the stellar core, the
fusion of “heavier elements” (e.g. gold, lead, uranium) can only
occur during “supernovae”.
 This is how we know that the Earth is made of “stardust”!
Birth of the
Solar System
 Our own solar system started to develop about
5.0 billion years ago when a cloud of gas and dust, the
product of earlier first- or second-generation
supernova explosions, began to contract due to gravity.
 As the cloud coalesced, its rotation rate increased (by
“conservation of angular momentum”) and it flattened
into a central ball of gas surrounded by a number of
rings of “stellar debris”.
 Over the next 300 million years, the central ball
became the Sun, and the rings evolved into “protoplanets” with “primordial” atmospheres, the third
closest of which would become planet Earth.