Right now, 2019 seems like a distant memory, but astronomers routinely cast their minds back much further in time to the very beginnings of the universe. With the help of the Hubble Space Telescope, researchers have been able to carry out this time travel to probe structures that existed within 500 million years of the Big Bang. But a study of the deepest observations ever made of distant galaxy clusters has shown that we need to look even further into the universe’s past to find the very first generation of stars.
Known as Population III stars, these stars are entirely composed of primordial gas (such as hydrogen, helium, and lithium) left-over from the Big Bang, and void of any heavier elements (such as oxygen, nitrogen, carbon, and iron) that are formed through processes in stellar cores. A team of European researchers on the hunt for these very first stars pulled out all the stops, probing galaxies 10 to 100 times fainter than any previously observed. But even within these early galaxies (dating to around 500 million to 1 billion years after the Big Bang), they found no evidence for the first generation of stars, suggesting that they formed even earlier than previously thought.
To even discover these galaxies is an incredible achievement. The team, led by Rachana Bhatawdekar of the European Space Agency, used Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys to find examples of the gravitational lensing effect – when light from a background star or galaxy is distorted by the immense gravitational field of an object directly in its foreground, such as a galaxy cluster. This magnifying effect, allows astronomers to observe objects otherwise too faint to be detected under the telescope’s normal capabilities.
Bhatawdekar and her team, whose results will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society, took this a step further and filtered out the light from the foreground galaxies, enabling them to discover galaxies with even lower masses, at distances equivalent to when the universe was less than a billion years old. But the stellar populations within these galaxies did not contain any evidence for the elusive first gen stars.
“These results have profound astrophysical consequences as they show that galaxies must have formed much earlier than we thought,” Bhatawdekar said in a statement.
Hopes are pinned on the upcoming James Webb Space Telescope to probe further into the universe’s past. Maybe one day these observations will provide astronomers with the first-ever evidence of the earliest stars.