01/04/2025
The universe also has eras!
Webb observed a surprising and extremely distant galaxy that existed 330 million years after the big bang, during what we call the universe’s “era of reionization.” This galaxy was emitting ultraviolet light at a specific wavelength that would typically have been absorbed by neutral hydrogen atoms prevalent at this point in the universe’s history. During the era of reionization, this neutral hydrogen was gradually ionized by the ultraviolet light emitted by newly forming stars. This is an ongoing process over hundreds of millions of years - and at just 330 million years after the big bang, there should still have been enough neutral hydrogen to shield this galaxy from Webb’s view - and yet Webb saw a strong signal from it.
(How did an infrared telescope see this galaxy emitting ultraviolet light? This galaxy is so distant that its light has been shifted towards the redder end of the electromagnetic spectrum by the expansion of the universe. As the space between objects stretches, any light in that space will also stretch. This effect is called redshift - and is why this galaxy’s ultraviolet light was perceived by us to be infrared.)
The implications of Webb seeing a signal from this galaxy are that perhaps the reionization process of neutral hydrogen started earlier than scientists think it did. Or perhaps there were some unexpectedly powerful sources of ionizing radiation early on in the galaxy’s history. What exactly those sources could be (maybe the much sought-after earliest generation of stars?) is still a mystery.
Read more: https://go.nasa.gov/3Xxo3tR
Credit: NASA, ESA, CSA, Brant Robertson (UC Santa Cruz), Ben Johnson (CfA), Sandro Tacchella (Cambridge), Phill Cargile (CfA), Joris Witstok (Cambridge, University of Copenhagen), P. Jakobsen (University of Copenhagen), Alyssa Pagan (STScI), Mahdi Zamani (ESA/Webb), JADES Collaboration
