Wednesday, October 14, 2009

Cosmic Dark Ages

Most folks are familiar with the historical concept of the Dark Ages. This term is applied to the time in Western European history between the fall of the Roman Empire and latter portion of the Middle Ages. This time is often considered by many to have a great lack of the light of knowledge. And so it was classified as a “dark” age in Western European history.

Now, did you know that in the cosmological theory of the Big Bang there was also a Dark Age? It is suggested that there was, but in this case it was a literal age of darkness.

Some time after the Big Bang, or the great expansion, as it is sometimes called, there was a time of about 800 million years when our universe had no light whatsoever. The energy from the Big Bang had subsided and cooled to the point that it no longer radiated visible light. The hydrogen and helium from the Big Bang may have begun to bunch and clump—the very beginning of star formation—but none had reached the stage where fusion would turn on in their cores and eventually cause their outer layers to shine. We are talking about a really, really dark time, here.

Astronomers want to study this time as part of their overall understanding of the universe formation, but how can they study what they cannot see? Well, rather than observing visible light, they are studying the radio-wave portion of the electromagnetic spectrum. They are hoping that this will allow them to look back to the end of this Dark Age, to the point when the first stars began to shine, when the first black holes began to accrete matter, and when the first galaxies began to form. These were the building blocks of the universe we see today.

Because the desired radio signals are so far away and so faint, it is easy to confuse them with background interference. So in order to detect the proper radio signals and filter out the background noise, the radio telescopes for the task must be really, really large. To meet this need, at least three projects are currently under construction. One is in the U.S., another is in Europe.

The U.S. project is the Long Wavelength Array (LWA), currently under construction in the desert west of Socorro, New Mexico. The final array, scheduled for completion in 2010, will consist of 13,000 antennas. The LWA is sponsored by the University of New Mexico, the Los Alamos National Laboratory, the Naval Research Laboratory and others.

The Europe project is the Low Frequency Array (LOFAR), which will stretch 5,000 antennas across northern Europe from a center in the Netherlands. LOFAR is currently scheduled for completion in 2011. The prime sponsor for LOFAR is ASTRON, the Netherlands Institute for Radio Astronomy. Astronomers in England, France, Germany, Poland and Sweden are also involved.

The Australia project is the Murchison Widefield Array (MWA), currently under construction near Mileura Station in Western Australia. The array will consist of 8,192 antennas spread across the western Australia outback. Because of its location, it is also called the Mileura Widefield Array. The MWA is sponsored by MIT, the National Science Foundation, the U.S. Air Force and the Australian Research Council.

These new radio telescopes will look for faint radio waves from the time the universe was 380,000 years to roughly a billion years old. The signals are coming from ancient hydrogen, which can be detected by a special line in the electromagnetic spectrum. Tiny variations in the hydrogen line indicate regions of slightly higher or lower density in the early universe. Over time, gravity accelerated the growth of these clumps, which became the seeds of the first generation of stars and galaxies.

Astronomers aren’t exactly sure about how long the Dark Age lasted, and they aren’t sure how much they will be able to detect of the end of this age and the beginning of star formation. Basically, they won’t know for sure about a lot of things until they try to find out. And of course, that’s what makes astronomers and other scientists so excited in the first place—trying to find things out.

To learn more about these three projects, and to learn a bit more about the cosmic Dark Age, check out these links:

The Long Wavelength Array (LWA)

The Netherlands Institute for Radio Astronomy, prime sponsor for LOFAR

The Murchison Widefield Array (MWA)

YouTube video, “Cosmic Dark Age – a time without stars,” an excerpt from the BBC Horizon Science documentary “The Death Start,” (BBC Worldwide, running time 3 minutes 47 seconds)


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