Example 1
Order these events: first stars, neutral atoms form, early light nuclei form.
Early light nuclei form → neutral atoms form as further cooling allows electrons to remain bound → first stars form later through gravitational collapse.
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Year 10
From a hot early universe to galaxies
Sequence expansion, cooling, nuclei, atoms, stars and galaxies at an introductory level.
Method and worked examples
The Big Bang model describes an early hot, dense universe that expanded and cooled. It is not an explosion from a central point into pre-existing empty space. As the universe cooled, particles could form light nuclei. Much later, electrons combined with nuclei to form neutral atoms, allowing light to travel more freely. Gravity eventually assembled gas into the first stars and galaxies.
The earliest universe produced mostly hydrogen and helium, with small amounts of some other light nuclei. Many heavier elements formed later through stellar processes and energetic stellar events. The universe is about 13.8 billion years old according to current cosmological evidence. Timeline drawings can compress different intervals, so check their scales. Planets and galaxies did not appear fully formed at the start.
Example 1
Example 2
Did all carbon and iron form during the first few minutes?
No. The early universe mainly formed light nuclei. Carbon, iron and many other heavier elements formed later through stellar processes.
Watch out: The model describes expansion of space from an early hot, dense state, without a special central explosion point.