The Star Formation

The story of star formation begins with an uneven universe. Right after the Big Bang, matter and energy were not spread out uniformly. Some regions were slightly denser than others, and those small differences mattered enormously. Where matter was packed a little more tightly, gravity pulled harder, and that stronger pull drew even more matter together. These growing clumps of matter became the seeds around which entire galaxies would eventually form.

A galaxy is a vast collection of stars, and the distances involved are staggering. Galaxies are spread over distances measured in thousands of light-years, and a single galaxy's diameter typically ranges from 80,000 to 150,000 light-years. To understand what that means, you have to understand what a light-year actually is — and it is not a measure of time, despite the word "year" in it. A light-year is a measure of distance: the distance light travels in one year. Light moves at 300,000 kilometres per second, so in a single year it covers roughly 9.461 × 10¹² kilometres. That is one light-year. For a sense of scale, the mean distance between the Sun and the Earth is about 149,598,000 kilometres — which, in light-years, comes to just 8.311 minutes of travel time. The Sun–Earth gap is measured in light-minutes; a galaxy is measured in tens of thousands of light-years. …