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 sec!) secThe universe was grapefruit-sized; some matter had appeared, but it was in an “unconventional” form (quarks, leptons etc); the temperature was K. no light!

Birth of the Universe AgeWhat Was Happening secThe first “conventional” matter had appeared (electrons, neutrinos and their anti-particles); the temperature was K. 2 secAll matter was in “conventional” form (including protons and neutrons); no atoms had yet formed; the temperature was K. 3 minSome atomic nuclei had “fused” (deuterium, helium-3 and helium-4); there were still no atoms; the temperature was 10 9 K. no light! still

Birth of the Universe AgeWhat Was Happening 10 6 yrsNuclei 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 yrsDue to gravity, “clumps” had begun to form within the expanding gas cloud; these would continue contracting to become the first stars! no light! still

Stellar Evolution 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 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 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 “proto- planets” with “primordial” atmospheres, the third closest of which would become planet Earth.