Our complex universe—chock full of galaxies, black holes and quasars—didn’t just appear after the Big Bang. For tens of millions of years, the universe was a dark expanse, full of ionized hydrogen and helium. But at some point—researchers aren’t sure when—these swirling gasses ignited the first stars. It’s a period known as Cosmic Dawn.
Now, as Jonathan Amos at the BBC reports, scientists have found traces of some of those first stars, suggesting they winked to life roughly 250 million years after the Big Bang.
As Ethan Siegal at Forbes reports, our current generation of telescopes, like the Hubble Space Telescope, just aren’t equipped to peer into the deepest depths of space and time. The oldest and furthest galaxy directly detected is GNZ-11, which formed just 400 million years after the Big Bang. But scientists believe that the first stars began to flicker on sometime between 380,000 years after the Big Bang and the emergence of early galaxies like GNZ-11.
Many astronomers have hypothesized that the first stars lit up around 200 million years after the Big Bang. But we haven’t successfully caught a glimpse of these stars. After billions of years of travel their light shifts into the infrared end of the spectrum, making it harder to detect without specially equipped IR telescopes. And the earliest stars are often shrouded in a soup of neutral particles that absorb their faint flickers.
That’s why, for this new study in the journal Nature, an international team of astronomers relied on indirect evidence, searching instead for signatures of oxygen and helium—elements that can only be created in the cores of stars.
As Amos explains, the researchers turned their sights to galaxy MACS1149-JD1, which lies billions of light years away, using two Earth-bound telescopes: the Atacama Large Millimetre/Submillimetre Array (Alma) and the European Southern Observatory's Very Large Telescope (VLT).
They found that over billions of years, the expansion of the universe shifts that light. And by analyzing that shift, researchers figured out the age of the oxygen and hydrogen signatures, even though they can’t directly see the galaxy.
Richard Ellis, a professor of astrophysics at University College London and co-author of the study, tells Amos that this oxygen has a redshift of 9.1. “That means the Universe has expanded nine to 10 times since the light left this object. We’re looking back about 97 percent of the way to the Big Bang [13.8 billion years ago] when the Universe was only about 500 million years old,” he says.
According to a press release, the team then used infrared spectroscopy from NASA’s Spitzer and Hubble Space Telescope to look at the brightness of JD1. Using that brightness and the best model of star development they were able to deduce the age of the stars in JD1.
“That gives us an indication of how much earlier in the history of the Universe—which we can’t currently probe with our telescopes—that this object actually formed,” Ellis tells Amos. “And we find this galaxy formed its stars when the Universe was only 250 million years old, which is like 2 percent of the present age of the Universe.”
Though a good start, peering even further into space and time will take some extra firepower. The James Webb Space Telescope, whose launch has been delayed from 2018 to 2020, will be equipped with sensors that allow it to view infrared starlight and penetrate the haze of the early universe, perhaps helping us directly observe the first starlight.
“Determining when cosmic dawn occurred is akin to the `Holy Grail' of cosmology and galaxy formation,” Ellis says in another press release. With this latest study, he says, “there is renewed optimism we are getting closer and closer to witnessing directly the birth of starlight. Since we are all made of processed stellar material, this is really finding our own origins.”