Where are the very first stars hiding?

Stars like the Sun are made largely from waste – leftover matter ejected billions of years ago during the death of previous star generations. We know this is the case from their content of heavy elements, their metallicity. When the universe was still young, there was only hydrogen, helium, and a little lithium, nothing else. These elements formed the very first stars a long, long time ago. The first stars are called “Population III” stars, while the current generation, which also includes the Sun, is called Population I. Population I was born from the ashes of Population II, just like Population II was created from the remnants of Population III.

However, Population III stars are difficult to find. At first, this seems logical: these stars were huge and had only a short life. Luckily, thanks to the limited speed of light, astronomers can look far into the past with the help of telescopes like Hubble. Objects that are more than ten billion light-years away we can watch as they progress through their youth, even though they have long ago ceased to exist. The gravitational lensing effect is particularly helpful for seeing into the past. Galaxies in the foreground act like lenses and bend the light from objects behind.

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