Cosmic Fog and the Era of Reionization
During the first billion years after the Big Bang, vast amounts of neutral hydrogen filled the space between galaxies, creating a cosmic fog that absorbed ultraviolet radiation and prevented light from traveling freely across the universe. This phase transition eventually cleared the opacity by ionizing the majority of hydrogen in intergalactic space, allowing starlight to reach distant observers today. Reionization began approximately 13 billion years ago.
Astronomers have long studied how ultraviolet photons managed to escape early galaxies during this period. For years, the leading explanation centered on supernovae. These powerful explosions generate massive galactic winds that sweep through galaxies, pushing gas and dust outward to clear pathways for radiation.
Hubble Space Telescope Data Reverses the Leading Supernova Theory
New observations from the Hubble Space Telescope are challenging that established mechanism. An international research team analyzed nearby starburst galaxies, where stars form at exceptionally high rates, to measure the speeds of their galactic winds. The findings suggest powerful explosions from dying stars may actually interfere with the process they were once believed to drive.
“Basically, how these galaxies were leaking ionizing radiation isn’t what we thought,” Cody Carr, lead author of the study from the University of Michigan, said in a statement. Instead of clearing a path for ultraviolet light, energy and winds from supernovae appear to redistribute gas and dust in ways that suppress the escape of ionizing photons. Observations show these photons are actually escaping before galactic winds form.
Stellar Activity and Unresolved Questions in Early Astronomy
With supernovae winds appearing to hinder rather than help radiation escape, researchers are looking closely at alternative mechanisms. Activity from young stars may hold the key, as radiation and smaller winds operating in their immediate neighborhoods could create openings in the surrounding gas before major stellar explosions occur. Renyue Cen, a professor and director of the Center for Cosmology and Computational Astrophysics at Zhejiang University and a senior author of the study, emphasized the need to examine how radiation and winds from young stars shape surrounding gas prior to the first supernovae explosions.
Published in Nature Astronomy, the study highlights gaps in current cosmological models. The research team is currently working to secure additional observing time on Hubble to examine more galaxies and further test the behavior of smaller stellar winds.
“We don’t know exactly what objects caused reionization or how it evolved,” Carr stated regarding the ongoing investigation into the universe’s phase transition.
Frequently Asked Questions About Cosmic Reionization
What caused the ancient cosmic fog in the early universe?
Vast amounts of neutral hydrogen filled the space between galaxies during the first billion years after the Big Bang, absorbing ultraviolet radiation and making the universe opaque to light.
When did the period known as reionization begin?
Reionization began approximately 13 billion years ago, eventually ionizing the majority of hydrogen in intergalactic space and allowing starlight to travel freely.
How do nearby starburst galaxies help astronomers study the early universe?
Starburst galaxies form stars at exceptionally high rates, resembling some of the systems that drove the universe’s early transformation and providing researchers a way to investigate how radiation escapes.