Among the most fundamental questions in astronomy are: How did the first stars and galaxies form? NASA’s James Webb Space Telescope is already providing new insights into this question.

One of the biggest programs in the first year of Webb’s surveys is the JWST Advanced Deep Extragalactic Survey, or JADES, which will spend about 32 days of telescope time to uncover and characterize faint, distant galaxies.

While the data is still being released, JADES has already discovered hundreds of galaxies that existed when the universe was less than 600 million years old.

The team of researchers has also spotted galaxies twinkling with many young stars.

“With JADES, we want to answer many questions, such as: How did the first galaxies assemble? How fast did stars form? Why do some galaxies stop forming stars?’ said Marcia Rieke of the University of Arizona in Tucson, co-director of the JADES program.

Ryan Endsley of the University of Texas at Austin led a survey of galaxies that existed 500 to 850 million years after the Big Bang.

This was a critical period known as the Age of Reunion. For hundreds of millions of years after the Big Bang, the universe was filled with a gaseous haze that made it opaque to energetic light. A billion years after the Big Bang, the haze had cleared and the universe became transparent, a process known as reionization. Scientists have debated whether active, supermassive black holes or galaxies full of young stars were the main cause of reionization.

As part of the JADES program, Endsley and his colleagues studied these galaxies with Webb’s NIRSpec (Near-Infrared Spectrograph) instrument to look for signatures of star formation—and found them in abundance.

“Almost every galaxy we find shows these unusually strong emission line signatures that indicate intense recent star formation. Those early galaxies were very good at making hot, massive stars,” Endsley said.

These bright, massive stars pumped out floods of ultraviolet light, which turned the surrounding gas from opaque to transparent by ionizing atoms, stripping electrons from their nuclei. Since these early galaxies had such a large population of hot, massive stars, they may have been the main driver of the reionization process. The subsequent recombination of electrons and nuclei produces the distinctly strong emission lines.

Endsley and his colleagues also found evidence that these young galaxies underwent periods of rapid star formation interspersed with quiet periods where fewer stars were formed. These mergers and launches may have occurred as galaxies captured clumps of gaseous raw materials needed to form stars. Alternatively, since massive stars explode rapidly, they may have injected energy into the surrounding environment periodically, preventing the gas from condensing to form new stars.