The Hubble Space telescope’s newest camera is already filling in gaps in astronomers’ understanding of events previously too distant and remote to be studied accurately. The Wide Field Camera 3, or WFC3, was installed in May of this year and was expected to become the Hubble’s new primary instrument. With a higher resolution and wider field of view, and the ability to view near-infrared light, visible light, and near-ultraviolet radiation, the WFC3 was expected to be 15-35 times more powerful than existing cameras. This heightened capacity was expected to be put to use primarily in studies of dark energy and dark matter, the observation of the formation of individual stars, and observation of distant galaxies that have never before been accessible for study. Already, the WFC3 is living up to expectations and answering long-held questions about the very beginnings of the universe.
With this heightened telescopic acuity, there has been a flurry of research concerning a period of early galaxy formation known as the reionization epoch, a period that has remained largely a mystery up until now. A recent study by an American and Japanese team of astronomers led by Carnegie Observatory’s Masami Ouchi, has been able to precisely determine the age and distance of some of the universe’s oldest galaxies, and in doing so has answered a question that has been puzzling astronomers for ages.
The Big Bang, an event estimated to have occurred approximately 13.7 billion years ago, created a hot, chaotic soup of free-floating atomic particles. A mere 400,000 years later, the atomic particles combined to form neutral hydrogen molecules, or H2. Sometime in the next 600,000 years, these neutral hydrogen molecules began to form enormous stars, which in turn emitted radiation and newly charged hydrogen ions, clearing the soup and allowing visible light to be emitted.
This much has been known for some time, but what has puzzled scientists up until very recently was how long, exactly, after the formation of the neutral hydrogen particles did reionization occur? Furthermore, when it did occur, did it happen suddenly, like the Big Bang itself? Or was it a gradual process, evolving over time?
Using the WFC3 as well as the Subaru telescope (from the National Astronomical Observatory of Japan) and the Spitzer telescope (out of California), researchers are able to calculate the specific wavelength of some of these earliest galaxies, which can then be used to calculate the galaxy’s distance and age. To do this, scientists view the distant stars through a progression of red light filters. As the filters increase in wavelength, or redness, distant stars will drop out of view, based on the wavelength of light they themselves are emitting. The last stars to drop out of view are determined to be the oldest stars, and as such are the stars of greatest interest to Ouchi and colleagues.
By examining density and brightness measurements, the team calculated that star formation and ionization rate was significantly lower from about 800 million to 1 billion years after the Big Bang than it was after that period. The low rate of ionization indicates that the reionization period must have started no less than 600 million years after the Big Bang.
The low rate of ionization during the period was the most unexpected finding, contradicting inferences made from previous studies. This could be partially explained by a difference in the types of stars that were formed during the period—stars produced in the early galaxies were massive, containing up to 200 times more matter than our sun. These massive stars produced more ionizing photons than would a greater number of smaller stars, and thus might have given the illusion of a higher ionization rate.
A generation ago, this level of detailed research was the stuff of science fiction. Now, with technology advancing at an almost exponential rate, we can only imagine the possibilities that lie ahead.
