NASA | JPL-Caltech | Spitzer | 2019 May 08
NASA's Spitzer Space Telescope has revealed that some of the universe's earliest galaxies were brighter than expected. The excess light is a byproduct of the galaxies releasing incredibly high amounts of ionizing radiation. The finding offers clues to the cause of the Epoch of Reionization, a major cosmic event that transformed the universe from being mostly opaque to the brilliant starscape seen today.
- This deep-field view of the sky (center) taken by NASA's Hubble and Spitzer space telescopes is dominated by galaxies — including some very faint, very distant ones — circled in red. The bottom right inset shows the light collected from one of those galaxies during a long-duration observation. Credits: NASA/JPL-Caltech/ESA/Spitzer/P.Oesch/S.De Barros/I.Labbe
In a new study, researchers report on observations of some of the first galaxies to form in the universe, less than 1 billion years after the big bang (or a little more than 13 billion years ago). The data show that in a few specific wavelengths of infrared light, the galaxies are considerably brighter than scientists anticipated. The study is the first to confirm this phenomenon for a large sampling of galaxies from this period, showing that these were not special cases of excessive brightness, but that even average galaxies present at that time were much brighter in these wavelengths than galaxies we see today.
No one knows for sure when the first stars in our universe burst to life. But evidence suggests that between about 100 million and 200 million years after the big bang, the universe was filled mostly with neutral hydrogen gas that had perhaps just begun to coalesce into stars, which then began to form the first galaxies. By about 1 billion years after the big bang, the universe had become a sparkling firmament. Something else had changed, too: Electrons of the omnipresent neutral hydrogen gas had been stripped away in a process known as ionization. The Epoch of Reionization — the changeover from a universe full of neutral hydrogen to one filled with ionized hydrogen — is well documented.
Before this universe-wide transformation, long-wavelength forms of light, such as radio waves and visible light, traversed the universe more or less unencumbered. But shorter wavelengths of light — including ultraviolet light, X-rays and gamma rays — were stopped short by neutral hydrogen atoms. These collisions would strip the neutral hydrogen atoms of their electrons, ionizing them.
But what could have possibly produced enough ionizing radiation to affect all the hydrogen in the universe? Was it individual stars? Giant galaxies? If either were the culprit, those early cosmic colonizers would have been different than most modern stars and galaxies, which typically don't release high amounts of ionizing radiation. Then again, perhaps something else entirely caused the event, such as quasars — galaxies with incredibly bright centers powered by huge amounts of material orbiting supermassive black holes. ...
Ancient galaxies reveal new clues about a cosmic transformation
University of California, Santa Cruz | 2019 May 08
The GREATS Hβ+ [OIII] Luminosity Function and Galaxy Properties at z∼8: Walking the Way of JWST ~ S. De Barros et al