One of the many profound questions about the birth of the universe is when the first stars and galaxies formed during cosmic creation. Those presumably massive first-generation Population III stars had to be composed of primordial gas: hydrogen, helium, and small amounts of lithium and beryllium, the only elements forged in the initial fireball and without any heavier elements (such as oxygen, nitrogen, carbon and iron) that are formed through processes in stellar nuclei. But Population III stars have never been observed, possibly because they all used up their nuclear fuel a long, long time ago and today only remnants remain.
But when exactly were they formed? And what effect did they have on the surrounding interstellar medium?
Traveling in time thanks to Hubble
A team of European astronomers has used the Hubble Space Telescope, data from the retired Spitzer Space Telescope and the Very Large Telescope (VLT) of the European Southern Observatory to study low-mass galaxies dating back between 500 million and 1 billion years. after the Big Bang.
To detect those faint galaxies, the experts studied six remote galaxy clusters with Hubble’s Wide Field Planetary Camera 3 and the Advanced Camera for Surveys. The combined mass of the galaxies within each cluster acts like a gravitational lens, magnifying the light from even more remote background galaxies. This magnification effect allows astronomers to observe objects that would otherwise be too faint to be detected under the normal capabilities of the telescope. The observations, made between 2012 and 2017, are among the deepest ever made, revealing galaxies 10 to 100 times fainter than previously seen.
However…
“We found no evidence for these first-generation Population III stars in this cosmic time interval,” said Rachana Bhatawdekar of the European Space Agency.
What does this mean?
Finding no evidence for the first generation of stars at what is believed to be the Hubble limit (when the universe was only 500 million years old) suggests that they formed even earlier than previously believed.
“These results have profound astrophysical consequences, as they show that galaxies must have formed much earlier than we thought,” Bhatawdekar said in a statement.
And now that?
Hopes are pinned on the James Webb Space Telescope – whose launch has been postponed to March 2021 – to further explore the universe’s past. Perhaps one day these observations will provide astronomers with the first evidence for the first stars.
Why are these stars called Population III and not Population I?
If they are the first stars in the universe, why are they called Population III? Well, in essence, because Population I “was already taken.” It was the name by which they classified the stars of the Milky Way, stars like the Sun, which are rich in heavier elements. And the name Population II was used to classify older stars in the Milky Way with a low content of heavy elements. Hence, only the name Population III remained to classify the stars that were forged from the primordial material that emerged from the Big Bang, approximately 13.8 billion years ago.
Reference: ESA / Hubble Information Center. “Hubble makes surprising find in the early universe.” ScienceDaily. ScienceDaily, June 3, 2020. The results appear in the next issue of the Monthly Reports of the Royal Astronomical Society and were also previously presented at the 236th meeting of the American Astronomical Society.
