What Was It Like When Galaxies Formed The Greatest Number Of Stars?
“The star-formation rate declined slowly and steadily for a few billion years, corresponding to an epoch where the Universe was still matter-dominated, just consisting of more processed and aged material. There were fewer mergers by number, but this was partially compensated for by the fact that larger structures were merging, leading to larger regions where stars formed.
But right around 6-to-8 billion years of age, the effects of dark energy began to make their presence known on the star formation rate, causing it to plummet precipitously. If we want to see the largest bursts of star formation, we have no choice but to look far away. The ultra-distant Universe is where star formation was at its maximum, not locally.”
In a myriad of locations, throughout our galaxy and almost all the galaxies in the known Universe, new stars form wherever a cloud of gas is triggered into collapsing. From the Orion Nebula to dozens of others in our own galaxy, new stars form thousands-at-a-time in regions all throughout our local neighborhood. But as spectacular as these sights are, they’re much, much rarer than they were a long time ago. In fact, we formed stars at a rate that was 30 times faster than today back when the Universe was young. For the last 11 billion years, we’ve been forming fewer and fewer stars everywhere we look.