Spitzer's deep-field view of the sky awash with galaxies. According to their findings, some of the Universe's earliest galaxies were brighter than expected. With the neutral hydrogen in the Universe, it would have taken a huge amount of radiation to make light, and it's unclear just what might have produced such radiation, whether newborn stars could have been enough, or luminous galaxies...
The online publication mentioned above writes that the surprising discovery of the bright galaxies could be able to bring new clues about one of the most significant cosmic events in the history of Universe: the Epoch of Reionization. Data collected for the study shows that in a few specific wavelengths of infrared light, some of the galaxies are much more illuminated than scientists anticipated, said a NASA press release. It's unknown when the universe's first stars appeared, however, evidence suggests that between approximately 100 million to 200 million years after the Big Bang, the universe was filled with neutral hydrogen gas that maybe started to combine into stars, which then kickstarted the formation of the first galaxies.
By 1 billion years after the Big Bang, the Universe was transparent and sparkling. 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.
To focus back in time just before the Epoch of Reionisation finished, scientists looked closely towards two regions of the sky for more than 200 hours each, allowing the space telescope to collect light that had traveled for more than 13 billion years to reach us.
As some of the longest science observations ever carried out by Spitzer, they were part of an observing campaign called GREATS, short for GOODS Re-ionization Era wide-Area Treasury from Spitzer. The study also used archival data from the NASA / ESA Hubble Space Telescope.
Using these ultra-deep observations by Spitzer, the team of astronomers observed 135 distant galaxies and found that they were all particularly bright in two specific wavelengths of infrared light produced by ionizing radiation interacting with hydrogen and oxygen gases within the galaxies. This implies that these galaxies were dominated by young, massive stars composed mostly of hydrogen and helium. They contain little measures of heavy elements (like nitrogen, carbon, and oxygen) contrasted with stars found in normal present-day systems.
Of course, those other factors - individual stars, incredibly bright quasars - may have contributed too. The Epoch of Reionisation wasn't just a single event and then BOOM, light was there; it was more like the slow lifting of a curtain, a process that took place over hundreds of millions of years.
"We did not expect that Spitzer, with a mirror no larger than a Hula-Hoop, would be capable of seeing galaxies so close to the dawn of time", said Michael Werner, Spitzer's project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.
"But nature is full of surprises, and the unexpected brightness of these early galaxies, together with Spitzer's superb performance, puts them within range of our small but powerful observatory".
Gareth Illingworth, a co-author on the study, said: "Our latest Spitzer result reveals how different these early galaxies are to those at later times and pinpoints our sample as a key set for providing insights into how galaxies so efficiently reionised the universe".
The Universe as we know it today, glittering with light, was something completely different at its outset: dark and murky.
"We discovered that galaxies in the early Universe were very different from today".
The Spitzer space telescope launched in 2003, and has made wonderful strides in infrared astronomy.