Roman Space Telescope of NASA Will Illuminate Cosmic Dawn

Today, vast stretches of space are crystal clear, but that wasn’t the case always. During its early stages (infancy), the cosmos was filled with a “fog” that made it opaque, cloaking the first galaxies and stars. NASA’s forthcoming Nancy Grace Roman Space Telescope will investigate the universe’s ensuing transition to the brilliant starscape we see today –– an era identified as cosmic dawn.

“Something very fundamental about the nature of the universe changed during this time,” said Michelle Thaller (an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland). “Thanks to Roman’s large, sharp infrared view, we may finally figure out what happened during a critical cosmic turning point.”

Lights Out, Lights On

Soon after its birth, the universe was a blistering sea of radiation and particles. As the cosmos expanded and cooled, positively charged protons were able to apprehend negatively charged electrons to form neutral atoms (mostly hydrogen, plus some helium). That was good news for the galaxies and stars the atoms would eventually become, but bad news for light!

It possibly took a long time for the gaseous hydrogen and helium to coalesce into stars, which then gravitated together to form the first galaxies. But even when stars started to shine, their light couldn’t reach very far before striking and being absorbed by neutral atoms. This epoch, known as the cosmic dark ages, lasted from around 380,000 to 200 million years post the big bang. Then the fog gradually lifted as more and more neutral atoms broke apart over the ensuing several hundred million years: an epoch called the cosmic dawn.

“We’re very curious about how the process happened,” said Aaron Yung (a Giacconi Fellow at the Space Telescope Science Institute in Baltimore), who is helping plan Roman Space Telescope’s early universe observations. “Roman’s large, crisp view of deep space will help us weigh different explanations.”

Prime Suspects

It could be that initial galaxies may be largely to blame for the energetic light that broke up the neutral atoms. The primary black holes may have played a role, too. Roman Space Telescope will look far and wide to scrutinize both possible culprits.

“Roman will excel at finding the building blocks of cosmic structures like galaxy clusters that later form,” said Takahiro Morishita (an assistant scientist at Caltech/IPAC in Pasadena, California), who has studied cosmic dawn. “It will quickly identify the densest regions, where more ‘fog’ is being cleared, making Roman a key mission to probe early galaxy evolution and the cosmic dawn.”

NASA’s JWST is also exploring cosmic dawn, using its narrower but deeper view to study the early cosmos. By combining Webb’s observations with Roman Space Telescope’s, scientists will generate a much more complete picture of this era.