Baby Galaxies Blowing Bubbles | astrobites
https://astrobites.org/2017/03/07/baby-galaxies-blowing-bubbles/
About four hundred thousand years after the Big Bang, the universe settled into a pretty dull period in its history. There were no stars or galaxies,
just one massive expanse of neutral hydrogen, sitting in the dark. This period in the universe’s history, known appropriately as the Dark Ages, came
abruptly to an end when the first stars were born and began to shine, dumping loads of high energy photons into their surroundings. These photons created
‘bubbles’ of ionised hydrogen around the stars, which slowly grew as more photons were pumped out by the stars. The bubbles surrounding the first stars
were pretty small, but later, as stars began to group together into the first galaxies, these bubbles were blown much bigger by the combined photons from
all the stars in the galaxy. Over time the bubbles from neighbouring galaxies began to overlap, until eventually all of the hydrogen in the universe was
ionised (see Figure 1). This process is known as reionisation (Astrobites has written plenty about reionisation in the past – for more background,
go check out some of these articles), and it’s a key period in the universe’s history.
